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\input texinfo @c -*-texinfo-*-
@c Copyright 2002 MySQL AB
@c
@c %**start of header
@setfilename internals.info
@c We want the types in the same index
@synindex cp fn
@iftex
@afourpaper
@end iftex
@c Get version and other info
@include include.texi
@ifclear tex-debug
@c This removes the black squares in the right margin
@finalout
@end ifclear
@c Set background for HTML
@set _body_tags BGCOLOR=#FFFFFF TEXT=#000000 LINK=#101090 VLINK=#7030B0
@settitle @strong{MySQL} Internals Manual for version @value{mysql_version}.
@setchapternewpage odd
@paragraphindent 0
@c %**end of header
@ifinfo
@format
START-INFO-DIR-ENTRY
* mysql-internals: (mysql-internals). @strong{MySQL} internals.
END-INFO-DIR-ENTRY
@end format
@end ifinfo
@titlepage
@sp 10
@center @titlefont{@strong{MySQL} Internals Manual}
@sp 10
@center Copyright @copyright{} 1998-2002 MySQL AB
@page
@end titlepage
@node Top, caching, (dir), (dir)
@ifinfo
This is a manual about @strong{MySQL} internals.
@end ifinfo
@menu
* caching:: How MySQL Handles Caching
* join_buffer_size::
* flush tables:: How MySQL Handles @code{FLUSH TABLES}
* filesort:: How MySQL Does Sorting (@code{filesort})
* selects:: How MySQL performs different selects
* transformations:: How MySQL transforms subqueries
* coding guidelines:: Coding Guidelines
* mysys functions:: Functions In The @code{mysys} Library
* DBUG:: DBUG Tags To Use
* protocol:: MySQL Client/Server Protocol
* Fulltext Search:: Fulltext Search in MySQL
* MyISAM Record Structure:: MyISAM Record Structure
* InnoDB Record Structure:: InnoDB Record Structure
* InnoDB Page Structure:: InnoDB Page Structure
* Files in MySQL Sources:: Annotated List Of Files in the MySQL Source Code Distribution
* Files in InnoDB Sources:: Annotated List Of Files in the InnoDB Source Code Distribution
@end menu
@node caching, join_buffer_size, Top, Top
@chapter How MySQL Handles Caching
@strong{MySQL} has the following caches:
(Note that the some of the filename have a wrong spelling of cache. :)
@table @strong
@item Key Cache
A shared cache for all B-tree index blocks in the different NISAM
files. Uses hashing and reverse linked lists for quick caching of the
last used blocks and quick flushing of changed entries for a specific
table. (@file{mysys/mf_keycash.c})
@item Record Cache
This is used for quick scanning of all records in a table.
(@file{mysys/mf_iocash.c} and @file{isam/_cash.c})
@item Table Cache
This holds the last used tables. (@file{sql/sql_base.cc})
@item Hostname Cache
For quick lookup (with reverse name resolving). Is a must when one has a
slow DNS.
(@file{sql/hostname.cc})
@item Privilege Cache
To allow quick change between databases the last used privileges are
cached for each user/database combination.
(@file{sql/sql_acl.cc})
@item Heap Table Cache
Many use of @code{GROUP BY} or @code{DISTINCT} caches all found rows in
a @code{HEAP} table. (This is a very quick in-memory table with hash index.)
@item Join buffer Cache
For every full join in a @code{SELECT} statement (a full join here means
there were no keys that one could use to find the next table in a list),
the found rows are cached in a join cache. One @code{SELECT} query can
use many join caches in the worst case.
@end table
@node join_buffer_size, flush tables, caching, Top
@chapter How MySQL uses the join_buffer cache
Basic information about @code{join_buffer_size}:
@itemize @bullet
@item
It's only used in the case when join type is of type @code{ALL} or
@code{index}; In other words: no possible keys can be used.
@item
A join buffer is never allocated for the first not-const table,
even it it would be of type @code{ALL}/@code{index}.
@item
The buffer is allocated when we need to do a each full join between two
tables and freed after the query is done.
@item
Accepted row combinations of tables before the @code{ALL}/@code{index}
able is stored in the cache and is used to compare against each read
row in the @code{ALL} table.
@item
We only store the used fields in the join_buffer cache, not the
whole rows.
@end itemize
Assume you have the following join:
@example
Table name Type
t1 range
t2 ref
t3 @code{ALL}
@end example
The join is then done as follows:
@example
- While rows in t1 matching range
- Read through all rows in t2 according to reference key
- Store used fields form t1,t2 in cache
- If cache is full
- Read through all rows in t3
- Compare t3 row against all t1,t2 combination in cache
- If rows satisfying join condition, send it to client
- Empty cache
- Read through all rows in t3
- Compare t3 row against all stored t1,t2 combinations in cache
- If rows satisfying join condition, send it to client
@end example
The above means that table t3 is scanned
@example
(size-of-stored-row(t1,t2) * accepted-row-cominations(t1,t2))/
join_buffer_size+1
@end example
times.
Some conclusions:
@itemize @bullet
@item
The larger the join_buff_size, the fewer scans of t3.
If @code{join_buff_size} is already large enough to hold all previous row
combinations then there is no speed to gain by making it bigger.
@item
If there is several tables of @code{ALL}/@code{index} then the we
allocate one @code{join_buffer_size buffer} for each of them and use the
same algorithm described above to handle it. (In other words, we store
the same row combination several times into different buffers)
@end itemize
@node flush tables, filesort, join_buffer_size, Top
@chapter How MySQL Handles @code{FLUSH TABLES}
@itemize @bullet
@item
Flush tables is handled in @file{sql/sql_base.cc::close_cached_tables()}.
@item
The idea of flush tables is to force all tables to be closed. This
is mainly to ensure that if someone adds a new table outside of
@strong{MySQL} (for example with @code{cp}) all threads will start using
the new table. This will also ensure that all table changes are flushed
to disk (but of course not as optimally as simple calling a sync on
all tables)!
@item
When one does a @code{FLUSH TABLES}, the variable @code{refresh_version}
will be incremented. Every time a thread releases a table it checks if
the refresh version of the table (updated at open) is the same as
the current @code{refresh_version}. If not it will close it and broadcast
a signal on @code{COND_refresh} (to wait any thread that is waiting for
all instanses of a table to be closed).
@item
The current @code{refresh_version} is also compared to the open
@code{refresh_version} after a thread gets a lock on a table. If the
refresh version is different the thread will free all locks, reopen the
table and try to get the locks again; This is just to quickly get all
tables to use the newest version. This is handled by
@file{sql/lock.cc::mysql_lock_tables()} and
@file{sql/sql_base.cc::wait_for_tables()}.
@item
When all tables has been closed @code{FLUSH TABLES} will return an ok
to client.
@item
If the thread that is doing @code{FLUSH TABLES} has a lock on some tables,
it will first close the locked tables, then wait until all other threads
have also closed them, and then reopen them and get the locks.
After this it will give other threads a chance to open the same tables.
@end itemize
@node filesort, selects, flush tables, Top
@chapter How MySQL Does Sorting (@code{filesort})
@itemize @bullet
@item
Read all rows according to key or by table scanning.
@item
Store the sort-key in a buffer (@code{sort_buffer}).
@item
When the buffer gets full, run a @code{qsort} on it and store the result
in a temporary file. Save a pointer to the sorted block.
@item
Repeat the above until all rows have been read.
@item
Repeat the following until there is less than @code{MERGEBUFF2} (15)
blocks left.
@item
Do a multi-merge of up to @code{MERGEBUFF} (7) regions to one block in
another temporary file. Repeat until all blocks from the first file
are in the second file.
@item
On the last multi-merge, only the pointer to the row (last part of
the sort-key) is written to a result file.
@item
Now the code in @file{sql/records.cc} will be used to read through them
in sorted order by using the row pointers in the result file.
To optimize this, we read in a big block of row pointers, sort these
and then we read the rows in the sorted order into a row buffer
(@code{record_buffer}).
@end itemize
@node selects, transformations, flush tables, Top
@chapter How MySQL performs different selects
@node select steps,,,
@section Steps of select executing
Every select performed in such base steps:
@itemize
@item
JOIN::prepare
@itemize @bullet
@item
initialization and linking JOIN structure to st_select_lex
@item
fix_fields() for all items (after fix_fields we know everything
about item)
@item
moving HAVING to WHERE if possible
@item
initialization procedure if exists
@end itemize
@item
JOIN::optimize
@itemize @bullet
@item
single select optimization
@item
creation first temporary table if need
@end itemize
@item
JOIN::exec
@itemize @bullet
@item
performing select (may be created second temporary table)
@end itemize
@item
JOIN::cleanup
@itemize @bullet
@item
removing all temporary tables, other cleanup
@end itemize
@item
JOIN::reinit
@itemize @bullet
@item
prepare all structures to SELECT executing (with JOIN::exec)
@end itemize
@end itemize
@node select select_result
@section select_result CLASS
Very important role in SELECT performing have select_result class and
classes inherited from it (usually called with "select_" prefix). This
class provide interface for results transmitting.
Key methods in this class are following:
@itemize @bullet
@item
@strong{send_fields} sends giving item list headers (type, name, etc..)
@item
@strong{send_data} sends giving item list values as row of table of result
@item
@strong{send_error} send error to used used mainly for error interception,
making some operation and then ::send_error will be called.
@end itemize
For example there are fillowing select_result classes:
@itemize
@item
@strong{select_send} used for sending results though network layer
@item
@strong{select_export} used for exporting data to file
@item
@strong{multi_delete} used for multi-delete
@item
@strong{select_insert} used for INSERT ... SELECT ...
@item
@strong{multi_update} used for multi-update
@end itemize
@node select simple
@section SIMPLE or PRIMARY SELECT.
For performing single primary select SELECT used function mysql_select,
which:
@itemize @bullet
@item
allocate JOIN;
@item
JOIN::prepare;
@item
JOIN::optimize;
@item
JOIN::exec;
@item
JOIN::cleanup.
@end itemize
In previous versions of mysql all SELECTs was performed with help of this
function and mysql_select() was not divided on parts.
@node select structure
@section Structure Of Complex Select
There 2 structures which describe SELECTS:
@itemize @bullet
@item
st_select_lex (SELECT_LEX) it represent SELECT itself
@item
st_select_lex_unit (SELECT_LEX_UNIT) group several selects in bunch
@end itemize
and represent UNION operation (absence of UNION is union
with 1 SELECT and this structure present in any case). In future this
structure will be used for EXCEPT and INTERSECT.
For example:
@example
(SELECT ... )UNION(SELECT ... (SELECT...)...(SELECT...UNION...SELECT))
1 2 3 4 5 6 7
@end example
will be represent as
@example
------------------------------------------------------------------------
level 1
SELECT_LEX_UNIT(2)
|
+---------------+
| |
SELECT_LEX(1) SELECT_LEX(3)
|
--------------- | ------------------------------------------------------
| level 2
+-------------------+
| |
SELECT_LEX_UNIT(4) SELECT_LEX_UNIT(6)
| |
| +--------------+
| | |
SELECT_LEX(4) SELECT_LEX(5) SELECT_LEX(7)
------------------------------------------------------------------------
@end example
Note: single subselect 4 have it's own SELECT_LEX_UNIT.
Most upper SELECT_LEX_UNIT (#2 in example) stored in LEX.
First and most upper SELECT_LEX (#1 in example) stored in LEX, too.
This two structures always exist.
In time of creating or performing any JOIN::* operation
LEX::current_select point on appropriate SELECT_LEX.
Only during parsing global (for whole UNION) ORDER_BY & LIMIT clauses
LEX::current_select points to SELECT_LEX_UNIT of this unit to store this
parameter in this SELECT_LEX_UNIT (SELECT_LEX and SELECT_LEX_UNIT are
inherited from st_select_lex_node).
@node select union
@section Non-Subselect UNIONs Executing
Non subselect unions performed with help of mysql_union(). for now it
divided on following steps:
@itemize
@item
st_select_lex_unit::prepare
@itemize @bullet
@item
create temporary table for union results storing (if UNION witout
ALL option, 'distinct' parameter will be passed to table creation
procedure). Types/lengths of table's fields will be determinated
by first SELECT item list.
@item
create select_union (inherited from select_result) which will
write selects results in this temporary table
@item
allocate JOIN and perform JOIN::prepare for all SELECTs belonged
to UNION
@end itemize
@item
st_select_lex_unit::exec
@itemize @bullet
@item
delete rows from temporary table if it is not first call
@item
if first call call JOIN::optimize else JOIN::reinit and then
JOIN::exec for all SELECTs (select_union will write result for
temporary table). If union is cacheable and this method called
second, (third, ...) time it will do nothing.
@item
call mysql_select on temporary table with global ORDER BY and
LIMIT parameters after collecting results from all SELECTs.
@end itemize
@end itemize
As far as mysql_select need SELECT_LEX structure SELECT_LEX of first
SELECT of this UNION will be passed to it, but also fake_select_lex
parameter will be passed to mysql_select() too, to prevent linking
this SELECT_LEX with JOIN on this mysql_select() session.
PROBLEM: this fake select need workaround in many places.
@node select derived
@section Derived Tables Executing
Derived tables processing is first operation on any query. It performed
before creation list of tables of whole query and opening/locking this
tables.
If lex->derived_tables flag present will be scanned all SELECT_LEX (there
are list of all SELECT_LEX in reverse order (first SELECT in query will
be last in this list) lex->all_selects_list).
Pointer on derived table SELECT_LEX_UNIT stored in TABLE_LIST structure
(TABLE_LIST::derived). And for any table which have this pointer will
be called mysql_derived().
mysql_derived():
@itemize @bullet
@item
Creates list of all tables used in this query, opens and locks it
@item
Creates temporary table for storing results
@item
Creates union_result for writing result in this table
@item
Calls mysql_select or mysql_union for execute query
@item
Removes all derived table subtree from SELECTs tree (if it is
not EXPLAIN)
@item
Stores pointer to this temporary table in TABLE_LIST structure, then
this table will be used by outer query. This table table will not be
skipped in checking grants, because tables from which this table was
received was checked in mysql_derived.
@item
Links this temporary table in thd->derived_tables for removing after
query executing. this table will be closed in close_thread_tables if
second parameter of it (bool skip_derived) will be true.
@end itemize
@node select subselect
@section Subselects
In expression subselect represented by Item inherited from Item_subselect.
To hide difference in performing single SELECTs and UNIONs
Item_subselect use two different engines, which provide uniformed
interface for access to underplaid SELECT or UNION
(subselect_single_select_engine and subselect_union_engine, both are
inherited from subselect_engine).
Engine will be created in time of Item_select constructing
(Item_subselect::init method).
On Item_subselect::fix_fields() will be called engine->prepare().
Before calling any value getting method (val, val_int, val_str,
bring_value (in case of row result)) will be called engine->exec(),
which execute query or just do nothing if subselect is cacheable and
already executed.
Items inherited from provide it's own select_result classes. There are
2 type of it:
@itemize @bullet
@item
select_singlerow_subselect it store values of giving row in
Item_singlerow_subselect cache on send_data() call and report error
if Item_subselect have 'assigned' attribute.
@item
select_exists_subselect just store 1 as value of
Item_exists_subselect on send_data() call. As far as
Item_in_subselect and Item_allany_subselect inherited from
Item_exists_subselect, they use same select_result class.
@end itemize
Item_select will never call cleanup() procedure for JOIN. Every
JOIN::cleanup will call cleanup() for inner JOINs. Most upper
JOIN::cleanup will be called by mysql_select() or mysql_union().
@node select select engine
@section Single Select Engine
subselect_single_select_engine:
@itemize @bullet
@item
@strong{constructor} allocate JOIN and store pointers on SELECT_LEX and JOIN
@item
@strong{prepare()} call JOIN::prepare
@item
@strong{fix_length_and_dec()} prepare cache and receive type and
parameters of returning items (it called only by
Item_singlerow_subselect)
@item
@strong{exec()} drop 'assigned flag of Item_subselect. If called first time
JOIN::optimize and JOINexec(), else do nothing or JOIN::reinit()
JOIN::exec() depending of type of subquery.
@end itemize
@node select union engine
@section Union Engine
subselect_union_engine:
@itemize @bullet
@item
@strong{constructor} just store pointer to st_select_lex_union
(SELECT_LEX_UNION)
@item
@strong{prepare()} call st_select_lex_unit::prepare
@item
@strong{fix_length_and_dec()} prepare cache and receive type and
parameters (maximum of length) of returning items (it called
only by Item_singlerow_subselect)
@item
@strong{exec()} call st_select_lex_unit::exec(). st_select_lex_unit::exec()
can drop 'assigned' flag of Item_subselect if
st_select_lex_unit::item is not 0.
@end itemize
@node selectexplain
@section Explain Execution
For EXPLAIN result showing for every SELECT will be called mysql_select
with option SELECT_DESCRIBE.
For main UNION will be called mysql_explain_union.
mysql_explain_union call mysql_explain_select for every SELECT in given
union.
mysql_explain_select call mysql_select with SELECT_DESCRIBE.
mysql_select create JOIN for select (if it not exists, because if it
called for subselect JOIN can be created in JOIN::optimize of outer
query when it decided to calculate value of subselect). Then it call
JOIN::prepare, JOIN::optimize, JOIN exec and JOIN::cleanup as usual.
JOIN::exec called for SELECT with SELECT_DESCRIBE option call
select_describe.
select_describe return to user description of SELECT and call
mysql_explain_union for every inner UNION
PROBLEM: how it will work with global query optimization?
@node transformations, coding guidelines, selects, Top
@chapter How MySQL transforms subqueries
Item_subselect virtual method select_transformer is used to rewrite
subqueries. It is called from Item_subselect::init (which called in
Item_subselect constructor)
@node transformation IN
@section Item_in_subselect::select_transformer
Item_in_subselect::select_transformer is divided on two parts for
scalar left part and row left part:
@node transformation scalar IN
@subsection Scalar IN Subselect
To rewrite scalar IN subselect used method
Item_in_subselect::single_value_transformer, Scalar IN subselect will
be replaced with Item_in_optimizer.
Item_in_optimizer item is special boolean function. On value request
(one of val, val_int or val_str methods) it evaluate left expression of
IN by storing it value in cache item (one of Item_cache* items), then it
test cache is it NULL. If left expression (cache) is NULL then
Item_in_optimizer return NULL, else it evaluate Item_in_subselect.
Example queries.
@example
a) SELECT * from t1 where t1.a in (SELECT t2.a FROM t2);
b) SELECT * from t1 where t1.a in (SELECT t2.a FROM t2 GROUP BY t2.a);
@end example
@itemize
@item
Item_in_subselect inherit mechanism of getting value from
Item_exists_subselect.
@item
Select_transformer stores reference to left expression in its
conditions: (in WHERE in case 'a' and in a HAVING in case 'b')
@item
Item from item list of this select (t2.a) can be referred with special
reference (Item_ref_null_helper or Item_asterisk_remover).
This reference informs Item_in_optimizer if item (t2.a) is NULL by
setting the 'was_null' flag.
@item
The return value from Item_in_subselect will be evaluated as following:
@itemize @bullet
@item
If TRUE return true
@item
If NULL return null
@item
If FALSE and 'was_null' is set, return null
@item
return FALSE
@end itemize
@end itemize
<left_expression> IN (SELECT <item> ...) will be represented like
following:
@example
+-----------------+
|Item_in_optimizer|
+-----------------+
|
+---------------------+------------+
| |
+-----------------------+ +-----------------+
| <left_expression> | |Item_in_subselect|
| | +-----------------+
+-----------------------+ |
|<left_expression cache>| +-----------+-----------+
| | | |
+-----------------------+ | |
^ +----------+ +--------------------+
+<<<<<<<<<<<<<<<<<| Item_ref | +<<<|Item_ref_null_helper|
+----------+ V +--------------------+
V +--------------------+
+>>>| <item> |
+--------------------+
@end example
where '<<<<<<<<<' is reference in meaning of Item_ref.
Item_ref used for point to <left_expression cache>, because in time of
transformation we know only address of variable where pointer on cache
will be stored.
If select have ORDER BY clause it will be wiped out, because no sense in
ORDER BY without LIMIT here.
If IN subselect union condition of every select in UNION will be changed
personally.
Following is examples of IN transformations:
@example
a) <left_expression> IN (SELECT <item> FROM t
WHERE <where_exp>)
will be represented as
(SELECT 1 FROM t
WHERE <where_exp> and
Item_ref(<cached_left_expression>)=<Item_asterisk_remover(<Item>)>)
b) <left_expression> IN (SELECT <item> FROM t
HAVING <having_expr>
ORDER BY 1)
will be represented as
(SELECT <item> as ref_null_helper FROM t
HAVING <having_exp> AND
Item_ref(<cached_left_expression>) = ref_null_helper)
c) <left_expression> IN (SELECT <item> UNION ...)
will be represented as
(SELECT 1
HAVING Item_ref(<cached_left_expression>)=
<Item_asterisk_remover(<Item>)>
UNION ...)
(having without FROM is syntax error, but having condition is checked
even for subselect without FROM)
d) <left_expression> IN (select <item>)
will be completely replaced with <left_expression> = <item>
@end example
Now conditions (WHERE (a) or HAVING (b)) will be changed depends of
select in following way:
If subselect have HAVING , sum function or GROUP BY (case a) then item
list will be unchanged and Item_ref_null_helper reference will be
created on item list element. Condition will be added to HAVING condition.
If subselect have not HAVING, sum function or GROUP BY (case b) then:
@itemize @bullet
@item
@strong{item list} will be replaced with 1.
@item
@strong{<item>} from item list will be stored in Item_asterisk_remover, which
inherit from Item_ref_null_helper, but store item on which refer by
itself, and also it can resolve '*' item.
@item
@strong{<left_expression cache> = <Item_ref_null_helper>} will be added to
WHERE clause this item or to HAVING clause if this subselect have
no FROM clause and subselect is union (case c).
@end itemize
Single select without FROM will be reduced to just
<left_expression> = <item> without using Item_in_optimizer.
@node transformations row IN
@subsection Row IN Subselect
To rewrite row IN subselect used method
Item_in_subselect::row_value_transformer. It work in almost same way as
scalar analog, but work with Item_cache_row for caching left expression
and use references on elements of Item_cache_row.
To refer on item list it use Item_ref_on_list_position.
Item_ref_on_list_position::fix_fields will find item in item list of
subselect by number and create Item_ref_null_helper to refer on it. It
used to find reference when all '*' items will be translated in item
list. Subselect with have HAVING, sum functions or GROUP BY will
transformed in following way:
@example
ROW(l1, l2, ... lN) IN (SELECT i1, i2, ... iM FROM t HAVING <having_expr>)
will be following:
(SELECT i1, i2, ... iM FROM t
HAVING <having_expr> and
<cache_l1> = <ref_on_list_position(1)> AND
<cache_l2> = <ref_on_list_position(2)> AND
...
<cache_lN> = <ref_on_list_position(N)>)
@end example
In this way will be transformed select without FROM, too.
For other subselect it will be same but for WHERE clause.
@node transformations all any
@section Item_allany_subselect
Item_allany_subselect is inherited from Item_in_subselect.
ALL/ANY/SOME use same algorithm (and same method of Item_in_subselect)
as scalar IN, but use different function instead of '='.
ANY/SOME use same function that was listed after left expression.
ALL use inverted function, and all subselect passed as argument to
Item_func_not.
@node transformations singlerow
@section Item_singlerow_subselect
Item_singlerow_subselect will be rewritten only if it have not FROM
clause, it is not part of UNION and it is scalar subselect. For now will
not be converted subselects with field or reference on top of item list
(we can't change name of such items from one hand, but from other hand
we should assign to it name of whole subselect which will be reduced);
Following will not be reduced:
@example
SELECT a;
SELECT 1 UNION SELECT 2;
SELECT 1 FROM t1;
@end example
Following select will be reduced:
@example
SELECT 1;
SELECT a+2;
@end example
Such subselect will be completely replaced by its expression from item
list and its SELECT_LEX and SELECT_LEX_UNIT will be removed from
SELECT_LEX's tree.
But all Item_fields and Item_ref of that expression will be marked for
special fix_fields() procedure. fix_fields() for such Item will be
performed is same way as for items of inner subselect. Also if this
expression is Item_fields or Item_ref then name of this new item will
be same as name of this item (but not '(SELECT ...)'). It is done to
prevent broke references on such items from more inner subselects.
@node coding guidelines, mysys functions, transformations, Top
@chapter Coding Guidelines
@itemize @bullet
@item
We are using @uref{http://www.bitkeeper.com/, BitKeeper} for source management.
@item
You should use the @strong{MySQL} 4.0 source for all developments.
@item
If you have any questions about the @strong{MySQL} source, you can post these
to @email{dev-public@@mysql.com} and we will answer them. Please
remember to not use this internal email list in public!
@item
Try to write code in a lot of black boxes that can be reused or use at
least a clean, easy to change interface.
@item
Reuse code; There is already a lot of algorithms in MySQL for list handling,
queues, dynamic and hashed arrays, sorting, etc. that can be reused.
@item
Use the @code{my_*} functions like @code{my_read()}/@code{my_write()}/
@code{my_malloc()} that you can find in the @code{mysys} library instead
of the direct system calls; This will make your code easier to debug and
more portable.
@item
Try to always write optimized code, so that you don't have to
go back and rewrite it a couple of months later. It's better to
spend 3 times as much time designing and writing an optimal function than
having to do it all over again later on.
@item
Avoid CPU wasteful code, even where it does not matter, so that
you will not develop sloppy coding habits.
@item
If you can write it in fewer lines, do it (as long as the code will not
be slower or much harder to read).
@item
Don't use two commands on the same line.
@item
Do not check the same pointer for @code{NULL} more than once.
@item
Use long function and variable names in English. This makes your code
easier to read.
@item
Use @code{my_var} as opposed to @code{myVar} or @code{MyVar} (@samp{_}
rather than dancing SHIFT to seperate words in identifiers).
@item
Think assembly - make it easier for the compiler to optimize your code.
@item
Comment your code when you do something that someone else may think
is not ``trivial''.
@item
Use @code{libstring} functions (in the @file{strings} directory)
instead of standard @code{libc} string functions whenever possible.
@item
Avoid using @code{malloc()} (its REAL slow); For memory allocations
that only need to live for the lifetime of one thread, one should use
@code{sql_alloc()} instead.
@item
Before making big design decisions, please first post a summary of
what you want to do, why you want to do it, and how you plan to do
it. This way we can easily provide you with feedback and also
easily discuss it thoroughly if some other developer thinks there is better
way to do the same thing!
@item
Class names start with a capital letter.
@item
Structure types are @code{typedef}'ed to an all-caps identifier.
@item
Any @code{#define}'s are in all-caps.
@item
Matching @samp{@{} are in the same column.
@item
Put the @samp{@{} after a @code{switch} on the same line, as this gives
better overall indentation for the switch statement:
@example
switch (arg) @{
@end example
@item
In all other cases, @samp{@{} and @samp{@}} should be on their own line, except
if there is nothing inside @samp{@{} and @samp{@}}.
@item
Have a space after @code{if}
@item
Put a space after @samp{,} for function arguments
@item
Functions return @samp{0} on success, and non-zero on error, so you can do:
@example
if(a() || b() || c()) @{ error("something went wrong"); @}
@end example
@item
Using @code{goto} is okay if not abused.
@item
Avoid default variable initalizations, use @code{LINT_INIT()} if the
compiler complains after making sure that there is really no way
the variable can be used uninitialized.
@item
Do not instantiate a class if you do not have to.
@item
Use pointers rather than array indexing when operating on strings.
@end itemize
Suggested mode in emacs:
@example
(load "cc-mode")
(setq c-mode-common-hook '(lambda ()
(turn-on-font-lock)
(setq comment-column 48)))
(setq c-style-alist
(cons
'("MY"
(c-basic-offset . 2)
(c-comment-only-line-offset . 0)
(c-offsets-alist . ((statement-block-intro . +)
(knr-argdecl-intro . 0)
(substatement-open . 0)
(label . -)
(statement-cont . +)
(arglist-intro . c-lineup-arglist-intro-after-paren)
(arglist-close . c-lineup-arglist)
))
)
c-style-alist))
(c-set-style "MY")
(setq c-default-style "MY")
@end example
@node mysys functions, DBUG, coding guidelines, Top
@chapter Functions In The @code{mysys} Library
Functions in @code{mysys}: (For flags see @file{my_sys.h})
@table @code
@item int my_copy _A((const char *from, const char *to, myf MyFlags));
Copy file from @code{from} to @code{to}.
@item int my_delete _A((const char *name, myf MyFlags));
Delete file @code{name}.
@item int my_getwd _A((string buf, uint size, myf MyFlags));
@item int my_setwd _A((const char *dir, myf MyFlags));
Get and set working directory.
@item string my_tempnam _A((const char *pfx, myf MyFlags));
Make a unique temporary file name by using dir and adding something after
@code{pfx} to make name unique. The file name is made by adding a unique
six character string and @code{TMP_EXT} after @code{pfx}.
Returns pointer to @code{malloc()}'ed area for filename. Should be freed by
@code{free()}.
@item File my_open _A((const char *FileName,int Flags,myf MyFlags));
@item File my_create _A((const char *FileName, int CreateFlags, int AccsesFlags, myf MyFlags));
@item int my_close _A((File Filedes, myf MyFlags));
@item uint my_read _A((File Filedes, byte *Buffer, uint Count, myf MyFlags));
@item uint my_write _A((File Filedes, const byte *Buffer, uint Count, myf MyFlags));
@item ulong my_seek _A((File fd,ulong pos,int whence,myf MyFlags));
@item ulong my_tell _A((File fd,myf MyFlags));
Use instead of open, open-with-create-flag, close, read, and write
to get automatic error messages (flag @code{MYF_WME}) and only have
to test for != 0 if error (flag @code{MY_NABP}).
@item int my_rename _A((const char *from, const char *to, myf MyFlags));
Rename file from @code{from} to @code{to}.
@item FILE *my_fopen _A((const char *FileName,int Flags,myf MyFlags));
@item FILE *my_fdopen _A((File Filedes,int Flags,myf MyFlags));
@item int my_fclose _A((FILE *fd,myf MyFlags));
@item uint my_fread _A((FILE *stream,byte *Buffer,uint Count,myf MyFlags));
@item uint my_fwrite _A((FILE *stream,const byte *Buffer,uint Count, myf MyFlags));
@item ulong my_fseek _A((FILE *stream,ulong pos,int whence,myf MyFlags));
@item ulong my_ftell _A((FILE *stream,myf MyFlags));
Same read-interface for streams as for files.
@item gptr _mymalloc _A((uint uSize,const char *sFile,uint uLine, myf MyFlag));
@item gptr _myrealloc _A((string pPtr,uint uSize,const char *sFile,uint uLine, myf MyFlag));
@item void _myfree _A((gptr pPtr,const char *sFile,uint uLine));
@item int _sanity _A((const char *sFile,unsigned int uLine));
@item gptr _myget_copy_of_memory _A((const byte *from,uint length,const char *sFile, uint uLine,myf MyFlag));
@code{malloc(size,myflag)} is mapped to these functions if not compiled
with @code{-DSAFEMALLOC}.
@item void TERMINATE _A((void));
Writes @code{malloc()} info on @code{stdout} if compiled with
@code{-DSAFEMALLOC}.
@item int my_chsize _A((File fd, ulong newlength, myf MyFlags));
Change size of file @code{fd} to @code{newlength}.
@item void my_error _D((int nr, myf MyFlags, ...));
Writes message using error number (see @file{mysys/errors.h}) on @code{stdout},
or using curses, if @code{MYSYS_PROGRAM_USES_CURSES()} has been called.
@item void my_message _A((const char *str, myf MyFlags));
Writes @code{str} on @code{stdout}, or using curses, if
@code{MYSYS_PROGRAM_USES_CURSES()} has been called.
@item void my_init _A((void ));
Start each program (in @code{main()}) with this.
@item void my_end _A((int infoflag));
Gives info about program.
If @code{infoflag & MY_CHECK_ERROR}, prints if some files are left open.
If @code{infoflag & MY_GIVE_INFO}, prints timing info and malloc info
about program.
@item int my_redel _A((const char *from, const char *to, int MyFlags));
Delete @code{from} before rename of @code{to} to @code{from}. Copies state
from old file to new file. If @code{MY_COPY_TIME} is set, sets old time.
@item int my_copystat _A((const char *from, const char *to, int MyFlags));
Copy state from old file to new file. If @code{MY_COPY_TIME} is set,
sets old time.
@item string my_filename _A((File fd));
Returns filename of open file.
@item int dirname _A((string to, const char *name));
Copy name of directory from filename.
@item int test_if_hard_path _A((const char *dir_name));
Test if @code{dir_name} is a hard path (starts from root).
@item void convert_dirname _A((string name));
Convert dirname according to system.
In MSDOS, changes all characters to capitals and changes @samp{/} to @samp{\}.
@item string fn_ext _A((const char *name));
Returns pointer to extension in filename.
@item string fn_format _A((string to,const char *name,const char *dsk,const char *form,int flag));
format a filename with replace of library and extension and
converts between different systems.
params to and name may be identicall
function dosn't change name if name != to
Flag may be: 1 force replace filnames library with 'dsk'
2 force replace extension with 'form' */
4 force Unpack filename (replace ~ with home)
8 Pack filename as short as possibly for output to
user.
All open requests should allways use at least:
"open(fn_format(temp_buffe,name,"","",4),...)" to unpack home and
convert filename to system-form.
@item string fn_same _A((string toname, const char *name, int flag));
Copys directory and extension from @code{name} to @code{toname} if neaded.
Copying can be forced by same flags used in @code{fn_format()}.
@item int wild_compare _A((const char *str, const char *wildstr));
Compare if @code{str} matches @code{wildstr}. @code{wildstr} can contain
@samp{*} and @samp{?} as wildcard characters.
Returns 0 if @code{str} and @code{wildstr} match.
@item void get_date _A((string to, int timeflag));
Get current date in a form ready for printing.
@item void soundex _A((string out_pntr, string in_pntr))
Makes @code{in_pntr} to a 5 char long string. All words that sound
alike have the same string.
@item int init_key_cache _A((ulong use_mem, ulong leave_this_much_mem));
Use caching of keys in MISAM, PISAM, and ISAM.
@code{KEY_CACHE_SIZE} is a good size.
Remember to lock databases for optimal caching.
@item void end_key_cache _A((void));
End key caching.
@end table
@node DBUG, protocol, mysys functions, Top
@chapter DBUG Tags To Use
Here is some of the tags we now use:
(We should probably add a couple of new ones)
@table @code
@item enter
Arguments to the function.
@item exit
Results from the function.
@item info
Something that may be interesting.
@item warning
When something doesn't go the usual route or may be wrong.
@item error
When something went wrong.
@item loop
Write in a loop, that is probably only useful when debugging
the loop. These should normally be deleted when one is
satisfied with the code and it has been in real use for a while.
@end table
Some specific to mysqld, because we want to watch these carefully:
@table @code
@item trans
Starting/stopping transactions.
@item quit
@code{info} when mysqld is preparing to die.
@item query
Print query.
@end table
@node protocol, Fulltext Search, DBUG, Top
@chapter MySQL Client/Server Protocol
@menu
* raw packet without compression::
* raw packet with compression::
* basic packets::
* communication::
* fieldtype codes::
* protocol functions::
* protocol version 2::
@end menu
@node raw packet without compression, raw packet with compression, protocol, protocol
@section Raw Packet Without Compression
@example
+-----------------------------------------------+
| Packet Length | Packet no | Data |
| 3 Bytes | 1 Byte | n Bytes |
+-----------------------------------------------+
@end example
@table @asis
@item 3 Byte packet length
The length is calculated with int3store
See include/global.h for details.
The max packetsize can be 16 MB.
@item 1 Byte packet no
If no compression is used the first 4 bytes of each packet is the header
of the packet. The packet number is incremented for each sent packet.
The first packet starts with 0.
@item n Byte data
@end table
The packet length can be recalculated with:
@example
length = byte1 + (256 * byte2) + (256 * 256 * byte3)
@end example
@node raw packet with compression, basic packets, raw packet without compression, protocol
@section Raw Packet With Compression
@example
+---------------------------------------------------+
| Packet Length | Packet no | Uncomp. Packet Length |
| 3 Bytes | 1 Byte | 3 Bytes |
+---------------------------------------------------+
@end example
@table @asis
@item 3 Byte packet length
The length is calculated with int3store
See include/global.h for details.
The max packetsize can be 16 MB.
@item 1 Byte packet no
@item 3 Byte uncompressed packet length
@end table
If compression is used the first 7 bytes of each packet
is the header of the packet.
@node basic packets, communication, raw packet with compression, protocol
@section Basic Packets
@menu
* ok packet::
* error packet::
@end menu
@node ok packet, error packet, basic packets, basic packets
@subsection OK Packet
For details, see @file{sql/net_pkg.cc::send_ok()}.
@example
+-----------------------------------------------+
| Header | No of Rows | Affected Rows |
| | 1 Byte | 1-8 Byte |
|-----------------------------------------------|
| ID (last_insert_id) | Status | Length |
| 1-8 Byte | 2 Byte | 1-8 Byte |
|-----------------------------------------------|
| Messagetext |
| n Byte |
+-----------------------------------------------+
@end example
@table @asis
@item Header
@item 1 byte number of rows ? (always 0 ?)
@item 1-8 bytes affected rows
@item 1-8 byte id (last_insert_id)
@item 2 byte Status (usually 0)
@item If the OK-packege includes a message:
@item 1-8 bytes length of message
@item n bytes messagetext
@end table
@node error packet, , ok packet, basic packets
@subsection Error Packet
@example
+-----------------------------------------------+
| Header | Status code | Error no |
| | 1 Byte | 2 Byte |
|-----------------------------------------------|
| Messagetext | 0x00 |
| n Byte | 1 Byte |
+-----------------------------------------------+
@end example
@table @asis
@item Header
@item 1 byte status code (0xFF = ERROR)
@item 2 byte error number (is only sent to new 3.23 clients.
@item n byte errortext
@item 1 byte 0x00
@end table
@node communication, fieldtype codes, basic packets, protocol
@section Communication
> Packet from server to client
< Paket from client tor server
Login
------
> 1. packet
Header
1 byte protocolversion
n byte serverversion
1 byte 0x00
4 byte threadnumber
8 byte crypt seed
1 byte 0x00
2 byte CLIENT_xxx options (see include/mysql_com.h
that is supported by the server
1 byte number of current server charset
2 byte server status variables (SERVER_STATUS_xxx flags)
13 byte 0x00 (not used yet).
< 2. packet
Header
2 byte CLIENT_xxx options
3 byte max_allowed_packet for the client
n byte username
1 byte 0x00
8 byte crypted password
1 byte 0x00
n byte databasename
1 byte 0x00
> 3. packet
OK-packet
Command
--------
< 1. packet
Header
1 byte command type (e.g.0x03 = query)
n byte query
Result set (after command)
--------------------------
> 2. packet
Header
1-8 byte field_count (packed with net_store_length())
If field_count == 0 (command):
1-8 byte affected rows
1-8 byte insert id
2 bytes server_status (SERVER_STATUS_xx)
If field_count == NULL_LENGTH (251)
LOAD DATA LOCAL INFILE
If field_count > 0 Result Set:
> n packets
Header Info
Column description: 5 data object /column
(See code in unpack_fields())
Columninfo for each column:
1 data block table_name
1 byte length of block
n byte data
1 data block field_name
1 byte length of block...
n byte data
1 data block display length of field
1 byte length of block
3 bytes display length of filed
1 data block type field of type (enum_field_types)
1 byte length of block
1 bytexs field of type
1 data block flags
1 byte length of block
2 byte flags for the columns (NOT_NULL_FLAG, ZEROFILL_FLAG....)
1 byte decimals
if table definition:
1 data block default value
Actual result (one packet per row):
4 byte header
1-8 byte length of data
n data
@node fieldtype codes, protocol functions, communication, protocol
@section Fieldtype Codes
@example
display_length |enum_field_type |flags
----------------------------------------------------
Blob 03 FF FF 00 |01 FC |03 90 00 00
Mediumblob 03 FF FF FF |01 FC |03 90 00 00
Tinyblob 03 FF 00 00 |01 FC |03 90 00 00
Text 03 FF FF 00 |01 FC |03 10 00 00
Mediumtext 03 FF FF FF |01 FC |03 10 00 00
Tinytext 03 FF 00 00 |01 FC |03 10 00 00
Integer 03 0B 00 00 |01 03 |03 03 42 00
Mediumint 03 09 00 00 |01 09 |03 00 00 00
Smallint 03 06 00 00 |01 02 |03 00 00 00
Tinyint 03 04 00 00 |01 01 |03 00 00 00
Varchar 03 XX 00 00 |01 FD |03 00 00 00
Enum 03 05 00 00 |01 FE |03 00 01 00
Datetime 03 13 00 00 |01 0C |03 00 00 00
Timestamp 03 0E 00 00 |01 07 |03 61 04 00
Time 03 08 00 00 |01 0B |03 00 00 00
Date 03 0A 00 00 |01 0A |03 00 00 00
@end example
@node protocol functions, protocol version 2, fieldtype codes, protocol
@section Functions used to implement the protocol
This should be merged with the above one and changed to texi format
Raw packets
-----------
- The my_net_xxxx() functions handles the packaging of a stream of data
into a raw packet that contains a packet number, length and data.
- This is implemented for the server in sql/net_serv.cc.
The client file, libmysql/net.c, is symlinked to this file
The important functions are:
my_net_write() Store a packet (= # number of bytes) to be sent
net_flush() Send the packets stored in the buffer
net_write_command() Send a command (1 byte) + packet to the server.
my_net_read() Read a packet
Include files
-------------
- include/mysql.h is included by all MySQL clients. It includes the
MYSQL and MYSQL_RES structures.
- include/mysql_com.h is include by mysql.h and mysql_priv.h (the
server) and includes a lot of common functions and structures to
handle the client/server protocol.
Packets from server to client:
-----------------------------
sql/net_pkg.cc:
- Sending of error packets
- Sending of OK packets (= end of data)
- Storing of values in a packet
sql/sql_base.cc:
- Function send_fields() sends the field description to the client.
sql/sql_show.cc:
- Sends results for a lot of SHOW commands, including:
SHOW DATABASES [like 'wildcard']
SHOW TABLES [like 'wildcard']
Packets from client to server:
------------------------------
This is done in libmysql/libmysql.c
The important ones are:
- mysql_real_connect() Connects to a mysqld server
- mysql_real_query() Sends a query to the server and
reads the ok packet or columns header.
- mysql_store_result() Read a result set from the server to memory
- mysql_use_result() Read a result set row by row from the server.
- net_safe_read() Read a packet from the server with
error handling.
- net_field_length() Reads the length of a packet string.
- simple_command() Sends a command/query to the server.
Connecting to mysqld (the MySQL server)
---------------------------------------
- On the client side: libmysql/libmysql.c::mysql_real_connect().
- On the server side: sql/sql_parse.cc::check_connections()
The packets sent during a connection are as follows
Server: Send greeting package (includes server capabilites, server
version and a random string of bytes to be used to scramble
the password.
Client: Sends package with client capabilites, user name, scrambled
password, database name
Server: Sends ok package or error package.
Client: If init command specified, send it t the server and read
ok/error package.
Password functions
------------------
The passwords are scrambled to a random number and are stored in hex
format on the server.
The password handling is done in sql/password.c. The important
function is 'scramble()', which takes the a password in clear text
and uses this to 'encrypt' the random string sent by the server
to a new message.
The encrypted message is sent to the server which uses the stored
random number password to encrypt the random string sent to the
client. If this is equal to the new message the client sends to the
server then the password is accepted.
@node protocol version 2, , protocol functions, protocol
@section Another description of the protocol
This should be merged with the above one and changed to texi format.
*****************************
*
* PROTOCOL OVERVIEW
*
*****************************
The MySQL protocol is relatively simple, and is designed for high performance
through minimisation of overhead, and extensibility through versioning and
options flags. It is a request-response protocol, and does not allow
multitasking or multiplexing over a single connection. There are two packet
formats, 'raw' and 'compressed' (which is used when both client and
server support zlib compression, and the client requests that data be
compressed):
* RAW PACKET, shorter than 16 M *
+-----------------------------------------------+
| Packet Length | Packet no | Data |
| 3 Bytes | 1 Byte | n Bytes |
+-----------------------------------------------+
^ ^
| 'HEADER' |
+-------------------------------+
* Packet Length: Calculated with int3store. See include/global.h for
details. The basic computation is length = byte1 +
(256 * byte2) + (256 * 256 * byte3). The max packetsize
can be 16 MB.
* Packet no: The packet number is incremented for each sent packet.
The first packet for each query from the client
starts with 0.
* Data: Specific to the operation being performed. Most often
used to send string data, such as a SQL query.
* COMPRESSED PACKET *
+---------------------------------------------------+-----------------+
| Packet Length | Packet no | Uncomp. Packet Length | Compressed Data |
| 3 Bytes | 1 Byte | 3 Bytes | n bytes |
+---------------------------------------------------+-----------------+
^ ^
| 'HEADER' |
+---------------------------------------------------+
* Packet Length: Calculated with int3store. See include/my_global.h for
details. The basic computation is length = byte1 +
(256 * byte2) + (256 * 256 * byte3). The max packetsize
can be 16 MB.
* Packet no: The packet number is incremented for each sent packet.
The first packet starts with 0.
* Uncomp. Packet Length: The length of the original, uncompressed packet
If this is zero then the data is not compressed.
* Compressed Data: The original packet, compressed with zlib compression
When using the compressed protocol, the client/server will only compress
send packets where the new packet is smaller than the not compressed one.
In other words, some packets may be compressed while others will not.
The 'compressed data' is one or more packets in *RAW PACKET* format.
*****************************
*
* FLOW OF EVENTS
*
*****************************
To understand how a client communicates with a MySQL server, it is easiest
to start with a high-level flow of events. Each event section will then be
followed by details of the exact contents of each type of packet involved
in the event flow.
* *
* CONNECTION ESTABLISHMENT *
* *
Clients connect to the server via a TCP/IP socket (port 3306 by default), a
Unix Domain Socket, or named pipes (on Windows). Once connected, the
following connection establishment sequence is followed:
+--------+ +--------+
| Client | | Server |
+--------+ +--------+
| |
| Handshake initialisation, including MySQL server version, |
| protocol version and options supported, as well as the seed |
| for the password hash |
| |
| <-------------------------------------------------------------- |
| |
| Client options supported, max packet size for client |
| username, password crypted with seed from server, database |
| name. |
| |
| --------------------------------------------------------------> |
| |
| 'OK' packet if authentication succeeds, 'ERROR' packet if |
| authentication fails. |
| |
| <-------------------------------------------------------------- |
| |
* HANDSHAKE INITIALISATION PACKET *
+--------------------------------------------------------------------+
| Header | Prot. Version | Server Version String | 0x00 |
| | 1 Byte | n bytes | 1 byte |
|--------------------------------------------------------------------|
| Thread Number | Crypt Seed | 0x00 | CLIENT_xxx options |
| | | | supported by server |
| 4 Bytes | 8 Bytes | 1 Byte | 2 Bytes |
|--------------------------------------------------------------------|
| Server charset no. | Server status variables | 0x00 padding |
| 1 Byte | 2 Bytes | 13 bytes |
+--------------------------------------------------------------------+
* Protocol version (currently '10')
* Server Version String (e.g. '4.0.5-beta-log'). Can be any length as
it's followed by a 0 byte.
* Thread Number - ID of server thread handling this connection
* Crypt seed - seed used to crypt password in auth packet from client
* CLIENT_xxx options - see include/mysql_com.h
* Server charset no. - Index of charset in use by server
* Server status variables - see include/mysql_com.h
* The padding bytes are reserverd for future extensions to the protocol
* CLIENT AUTH PACKET *
+--------------------------------------------------------------------+
| Header | CLIENT_xxx options supported | max_allowed_packet |
| | by client | for client |
| | 2 Bytes | 3 bytes |
|--------------------------------------------------------------------|
| User Name | 0x00 | Crypted Password | 0x00 | Database Name |
| n Bytes | 1 Byte | 8 Bytes | 1 Byte | n Bytes |
|--------------------------------------------------------------------|
| 0x00 |
| 1 Byte |
+--------------------------------------------------------------------+
* CLIENT_xxx options that this client supports:
#define CLIENT_LONG_PASSWORD 1 /* new more secure passwords */
#define CLIENT_FOUND_ROWS 2 /* Found instead of affected rows */
#define CLIENT_LONG_FLAG 4 /* Get all column flags */
#define CLIENT_CONNECT_WITH_DB 8 /* One can specify db on connect */
#define CLIENT_NO_SCHEMA 16 /* Don't allow database.table.column */
#define CLIENT_COMPRESS 32 /* Can use compression protocol */
#define CLIENT_ODBC 64 /* Odbc client */
#define CLIENT_LOCAL_FILES 128 /* Can use LOAD DATA LOCAL */
#define CLIENT_IGNORE_SPACE 256 /* Ignore spaces before '(' */
#define CLIENT_INTERACTIVE 1024 /* This is an interactive client */
#define CLIENT_SSL 2048 /* Switch to SSL after handshake */
#define CLIENT_IGNORE_SIGPIPE 4096 /* IGNORE sigpipes */
#define CLIENT_TRANSACTIONS 8192 /* Client knows about transactions */
* max_allowed_packet for the client (in 'int3store' form)
* User Name - user to authenticate as. Is followed by a null byte.
* Crypted Password - password crypted with seed given in packet from
server, see scramble() in sql/password.c
* Database name (optional) - initial database to use once connected
Is followed by a null byte
At the end of every client/server exchange there is either an 'OK' packet
or an 'ERROR' packet sent from the server. To determine whether a packet is
an 'OK' packet, or an 'ERROR' packet, check if the first byte (after the
header) is 0xFF. If it has the value of 0xFF, the packet is an 'ERROR'
packet.
* OK PACKET *
For details, see sql/net_pkg.cc::send_ok()
+-----------------------------------------------+
| Header | No of Rows | Affected Rows |
| | 1 Byte | 1-9 Byte |
|-----------------------------------------------|
| ID (last_insert_id) | Status | Length |
| 1-9 Byte | 2 Byte | 1-9 Byte |
|-----------------------------------------------|
| Messagetext |
| n Byte |
+-----------------------------------------------+
* Number of rows, always 0
* Affected rows
* ID (last_insert_id) - value for auto_increment column (if any)
* Status (usually 0)
In general, in the MySQL protocol, fields in a packet that that
represent numeric data, such as lengths, that are labeled as '1-9'
bytes can be decoded by the following logic:
If the first byte is '251', the
corresponding column value is NULL (only appropriate in
'ROW DATA' packets).
If the first byte is '252', the value stored can be read
from the following 2 bytes as a 16-bit integer.
If the first byte is '253' the value stored can be read
from the following 4 bytes as a 32-bit long integer
If the first byte is '254', the value stored can be read
from the following 8 bytes as a 64-byte long
Otherwise (values 0-250), the value stored is the value of the
first byte itself.
If the OK-packet includes a message:
* Length of message
* Message Text
* ERROR PACKET *
+-----------------------------------------------+
| Header | Status code | Error no |
| | 1 Byte | 2 Byte |
|-----------------------------------------------|
| Messagetext | |
| n Byte | |
+-----------------------------------------------+
* Status code (0xFF = ERROR)
* Error number (is only sent to 3.23 and newer clients)
* Error message text (ends at end of packet)
Note that the error message is not null terminated.
The client code can however assume that the packet ends with a null
as my_net_read() will always add an end-null to all read packets to
make things easier for the client.
Example:
Packet dump of client connecting to server:
+------------------------- Protocol Version (10)
|
| +---------------------- Server Version String (0x00 terminated)
| |
| |
0a 34 2e 30 2e 35 2d 62 . 4 . 0 . 5 - b
65 74 61 2d 6c 6f 67 00 e t a - l o g .
15 00 00 00 2b 5a 65 6c . . . . + Z e l
| |
| +------------ First 4 bytes of crypt seed
|
+------------------------ Thread Number
+------------------------- Last 4 bytes of crypt seed
|
| +-------- CLIENT_XXX Options supported by server
| |
| +-+--+ +--- Server charset index
| | | |
6f 69 41 46 00 2c 28 08 o i A F . , ( .
02 00 00 00 00 00 00 00 . . . . . . . .
| |
| +---------------------- 0x00 padding begins
|
+------------------------- Server status (0x02 =
SERVER_STATUS_AUTOCOMMIT)
00 00 00 00 00 00 00 00 . . . . . . . .
* Client Authentication Response (Username 'test', no database
selected) *
+--------------------- Packet Length (0x13 = 19 bytes)
|
| +--------------- Packet Sequence #
| |
| | +----------- CLIENT_XXX Options supported by client
| |
+---+---+ | +-+-+
| | | | |
13 00 00 01 03 00 1e 00 . . . . . . . .
00 74 65 73 74 00 48 5e . t e s t . H ^
| | |
+----+-----+ +------- Scrambled password, 0x00 terminated
|
+----------------- Username, 0x00 terminated
57 4a 4e 41 4a 4e 00 00 W J N A J N . .
00 .
>From this point on, the server waits for 'commands' from the client
which include queries, database shutdown, quit, change user, etc (see
the COM_xxxx values in include/mysql_com.h for the latest
command codes).
* *
* COMMAND PROCESSING *
* *
+--------+ +--------+
| Client | | Server |
+--------+ +--------+
| |
| A command packet, with a command code, and string data |
| when appropriate (e.g. a query), (see the COM_xxxx values |
| in include/mysql_com.h for the command codes) |
| |
| --------------------------------------------------------------> |
| |
| A 'RESULT' packet if the command completed successfully, |
| an 'ERROR' packet if the command failed. 'RESULT' packets |
| take different forms (see the details following this chart) |
| depending on whether or not the command returns rows. |
| |
| <-------------------------------------------------------------- |
| |
| n 'FIELD PACKET's (if rows are returned) |
| |
| <-------------------------------------------------------------- |
| |
| 'LAST DATA' packet |
| |
| <-------------------------------------------------------------- |
| |
| n 'ROW PACKET's (if rows are returned) |
| |
| <-------------------------------------------------------------- |
| |
| 'LAST DATA' packet |
| |
| <-------------------------------------------------------------- |
| |
* Command Packet *
+------------------------------------------------------+
| Header | Command type | Query (if applicable) |
| | 1 Byte | n Bytes |
+------------------------------------------------------+
* Command type: (e.g.0x03 = query, see the COM_xxxx values in
include/mysql_com.h)
* Query (if applicable)
Note that my_net_read() null-terminates all packets on the
receiving side of the channel to make it easier for the code
examining the packets.
The current command codes are:
0x00 COM_SLEEP
0x01 COM_QUIT
0x02 COM_INIT_DB
0x03 COM_QUERY
0x04 COM_FIELD_LIST
0x05 COM_CREATE_DB
0x06 COM_DROP_DB
0x07 COM_REFRESH
0x08 COM_SHUTDOWN
0x09 COM_STATISTICS
0x0a COM_PROCESS_INFO
0x0b COM_CONNECT
0x0c COM_PROCESS_KILL
0x0d COM_DEBUG
0x0e COM_PING
0x0f COM_TIME
0x10 COM_DELAYED_INSERT
0x11 COM_CHANGE_USER
0x12 COM_BINLOG_DUMP
0x13 COM_TABLE_DUMP
0x14 COM_CONNECT_OUT
0x15 COM_REGISTER_SLAVE
* Result Packet *
Result packet for a command returning _no_ rows:
+-----------------------------------------------+
| Header | Field Count | Affected Rows |
| | 1-9 Bytes | 1-9 Bytes |
|-----------------------------------------------|
| ID (last_insert_id) | Server Status |
| 1-9 Bytes | 2 Bytes |
+-----------------------------------------------+
* Field Count: Has value of '0' for commands returning _no_ rows
* Affected rows: Count of rows affected by INSERT/UPDATE/DELETE, etc.
* ID: value of auto_increment column in row (if any). 0 if
* Server Status: Usually 0
Result packet for a command returning rows:
+-------------------------------+
| Header | Field Count |
| | 1-9 Bytes |
+-------------------------------+
* Field Count: number of columns/fields in result set,
(packed with net_store_length() in sql/net_pkg.cc)
This is followed by as many packets as the number of fields ('Field Count')
that contain the metadata for each column/field (see unpack_fields() in
libmysql/libmysql.c):
* FIELD PACKET *
+-----------------------------------------------+
| Header | Table Name |
| | length-coded-string |
|-----------------------------------------------|
| Field Name |
| length-code-string |
|-----------------------------------------------|
| Display length of field
| length-coded-binary (4 bytes) |
|-----------------------------------------------|
| Field Type (enum_field_types in mysql_com.h) |
| length-coded-binary (2 bytes) |
|-----------------------------------------------|
| Field Flags | Decimal Places|
| length-coded-binary (3 bytes) | 1 Byte |
+--------------+-------------+------------------+
* A length coded string is a string where we first have a packet
length (1-9 bytes, packed_with net_store_length()) followed
by a string.
* A length coded binary is a length (1 byte) followed by an integer
value in low-byte-first order. For the moment this type is always
fixed length in this packet.
* Table Name - the name of the table the column comes from
* Field Name - the name of the column/field
* Display length of field - length of field
* Field Type - Type of field, see enum_field_types in
include/mysql_com.h
Current field types are:
0x00 FIELD_TYPE_DECIMAL
0x01 FIELD_TYPE_TINY
0x02 FIELD_TYPE_SHORT
0x03 FIELD_TYPE_LONG
0x04 FIELD_TYPE_FLOAT
0x05 FIELD_TYPE_DOUBLE
0x06 FIELD_TYPE_NULL
0x07 FIELD_TYPE_TIMESTAMP
0x08 FIELD_TYPE_LONGLONG
0x09 FIELD_TYPE_INT24
0x0a FIELD_TYPE_DATE
0x0b FIELD_TYPE_TIME
0x0c FIELD_TYPE_DATETIME
0x0d FIELD_TYPE_YEAR
0x0e FIELD_TYPE_NEWDATE
0xf7 FIELD_TYPE_ENUM
0xf8 FIELD_TYPE_SET
0xf9 FIELD_TYPE_TINY_BLOB
0xfa FIELD_TYPE_MEDIUM_BLOB
0xfb FIELD_TYPE_LONG_BLOB
0xfc FIELD_TYPE_BLOB
0xfd FIELD_TYPE_VAR_STRING
0xfe FIELD_TYPE_STRING
0xff FIELD_TYPE_GEOMETRY
* Field Flags - NOT_NULL_FLAG, PRI_KEY_FLAG, xxx_FLAG in
include/mysql_com.h
Note that the packet format in 4.1 has slightly changed to allow more values.
* ROW PACKET *
+-----------------------------------------------+
| Header | Data Length | Column Data | ....for each column
| | 1-9 Bytes | n Bytes |
+-----------------------------------------------+
* Data Length: (packed with net_store_length() in sql/net_pkg.cc)
If 'Data Length' == 0, this is an 'ERROR PACKET'.
* Column Data: String representation of data. MySQL always sends result set
data as strings.
* LAST DATA PACKET *
Packet length is < 9 bytes, and first byte is 0xFE
+--------+
| 0xFE |
| 1 Byte |
+--------+
Examples:
***********
*
* INITDB Command
*
***********
A client issuing an 'INITDB' (select the database to use) command,
followed by an 'OK' packet with no rows and no affected rows from
the server:
* INITDB (select database to use) 'COMMAND' Packet *
+--------------------- Packet Length (5 bytes)
|
| +--------------- Packet Sequence #
| |
| | +------------ Command # (INITDB = 0x02)
| |
+---+---+ | | +---------- Beginning of query data
| | | | |
05 00 00 00 02 74 65 73 . . . . . t e s
74 t
* 'OK' Packet with no rows, and no rows affected *
+--------------------- Packet Length (3 bytes)
|
| +--------------- Packet Sequence #
| |
+---+---+ |
| | |
03 00 00 01 00 00 00 . . . . . . .
***********
*
* SELECT query example
*
***********
Client issuing a 'SELECT *' query on the following table:
CREATE TABLE number_test (minBigInt bigint,
maxBigInt bigint,
testBigInt bigint)
* 'COMMAND' Packet with QUERY (select ...) *
+--------------------- Packet Length (26)
|
| +--------------- Packet Sequence #
| |
| | +------------ Command # (QUERY = 0x03)
| |
+---+---+ | | +---------- Beginning of query data
| | | | |
1a 00 00 00 03 53 45 4c . . . . . S E L
45 43 54 20 2a 20 66 72 E C T . * . f r
6f 6d 20 6e 75 6d 62 65 o m . n u m b e
72 5f 74 65 73 74 r _ t e s t
and receiving an 'OK' packet with a 'FIELD COUNT' of 3
* 'OK' Packet with 3 fields *
+--------------------- Packet Length (3 bytes)
|
| +--------------- Packet Sequence #
| |
+---+---+ |
| | |
01 00 00 01 03 . . . . .
Followed immediately by 3 'FIELD' Packets. Note, the individual packets
are delimitted by =======, so that all fields can be annotated in the first
'FIELD' packet example:
=============================================================
+--------------------- Packet Length (0x1f = 31 bytes)
|
| +--------------- Packet Sequence #
| |
| | +------------ Block Length (0x0b = 11 bytes)
| | |
+---+---+ | | +--------- Table Name (11 bytes long)
| | | | |
1f 00 00 02 0b 6e 75 6d . . . . . n u m
62 65 72 5f 74 65 73 74 b e r _ t e s t
+------------------------ Block Length (9 bytes)
|
| +--------------------- Column Name (9 bytes long)
| |
09 6d 69 6e 42 69 67 49 . m i n B i g I
6e 74 03 14 00 00 01 08 n t . . . . . .
| | | | |
| +---+---+ | +--- Field Type (0x08 = FIELD_TYPE_LONGLONG)
| | |
| | +------ Block Length (1)
| |
| +--------------- Display Length (0x14 = 20 chars)
|
+------------------ Block Length (3)
+------------------------ Block Length (2)
|
| +-------------------- Field Flags (0 - no flags set)
| |
| +---+ +--------------- Decimal Places (0)
| | | |
02 00 00 00 . . . .
=============================================================
'FIELD' packet for the 'number_Test.maxBigInt' column
1f 00 00 03 0b 6e 75 6d . . . . . n u m
62 65 72 5f 74 65 73 74 b e r _ t e s t
09 6d 61 78 42 69 67 49 . m a x B i g I
6e 74 03 14 00 00 01 08 n t . . . . . .
02 00 00 00 . . . .
=============================================================
'FIELD' packet for the 'number_test.testBigInt' column
20 00 00 04 0b 6e 75 6d . . . . . n u m
62 65 72 5f 74 65 73 74 b e r _ t e s t
0a 74 65 73 74 42 69 67 . t e st B i g
49 6e 74 03 14 00 00 01 I n t . . . . .
08 02 00 00 00 . . . . .
=============================================================
Followed immediately by one 'LAST DATA' packet:
fe 00 . .
Followed immediately by 'n' row packets (in this case, only
one packet is sent from the server, for simplicity's sake):
+--------------------- Packet Length (0x52 = 82 bytes)
|
| +--------------- Packet Sequence #
| |
| | +------------ Data Length (0x14 = 20 bytes)
| | |
+---+---+ | | +--------- String Data '-9223372036854775808'
| | | | | (repeat Data Length/Data sequence)
52 00 00 06 14 2d 39 32 . . . . . - 9 2
32 33 33 37 32 30 33 36 2 3 3 7 2 0 3 6
38 35 34 37 37 35 38 30 8 5 4 7 7 5 8 0
38 13 39 32 32 33 33 37 8 . 9 2 2 3 3 7
32 30 33 36 38 35 34 37 2 0 3 6 8 5 4 7
37 35 38 30 37 0a 36 31 7 5 8 0 7 . 6 1
34 37 34 38 33 36 34 37 4 7 4 8 3 6 4 7
Followed immediately by one 'LAST DATA' packet:
fe 00 . .
@c The Index was empty, and ugly, so I removed it. (jcole, Sep 7, 2000)
@c @node Index
@c @unnumbered Index
@c @printindex fn
@c @node 4.1 protocol,,,
@c @chapter MySQL 4.1 protocol
@node 4.1 protocol changes,,,
@section Changes to 4.0 protocol in 4.1
All basic packet handling is identical to 4.0. When communication
with an old 4.0 or 3.x client we will use the old protocol.
The new things that we support with 4.1 are:
@itemize @bullet
@item
Warnings
@item
Prepared statements
@item
Binary protocol (will be faster than the current protocol that
converts everything to strings)
@end itemize
What has changed in 4.1 are:
@itemize @bullet
@item
A lot of new field information (database, real table name etc)
@item
The 'ok' packet has more status fields
@item
The 'end' packet (send last for each result set) now contains some
extra information
@item
New protocol for prepared statements. In this case all parameters and
results will sent as binary (low-byte-first).
@end itemize
@node 4.1 field packet,,,
@section 4.1 field description packet
The field description packet is sent as a response to a query that
contains a result set. It can be distinguished from a ok packet by
the fact that the first byte can't be 0 for a field packet.
@xref{4.1 ok packet}.
The header packet has the following structure:
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 1-9 @tab Number of columns in result set (never 0)
@item 1-9 @tab Extra information sent be some command (SHOW COLUMNS
uses this to send the number of rows in the table)
@end multitable
This packet is always followed by a field description set.
@xref{4.1 field desc}.
@node 4.1 field desc,,,
@section 4.1 field description result set
The field description result set contains the meta info for a result set.
@multitable @columnfractions .20 .80
@item Type @tab Comment
@item string @tab Database name
@item string @tab Table name alias (or table name if no alias)
@item string @tab Real table name
@item string @tab Alias for column name (or column name if not used)
@item 11 byte @tab Fixed length fields in one field part:
@itemize
@item 2 byte int @tab Character set number
@item 3 byte int @tab Length of column definition
@item 1 byte int @tab Enum value for field type
@item 3 byte int @tab 2 byte column flags (NOT_NULL_FLAG etc..) + 1 byte number of decimals.
@item 2 byte int @tab zero (reserved for future use)
@end itemize
@item string int @tab Default value, only set when using mysql_list_fields().
@end multitable
@node 4.1 ok packet,,,
@section 4.1 ok packet
The ok packet is the first that is sent as an response for a query
that didn't return a result set.
The ok packet has the following structure:
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 1 @tab 0 ; Marker for ok packet
@item 1-9 @tab Affected rows
@item 1-9 @tab Last insert id (0 if one wasn't used)
@item 2 @tab Server status; Can be used by client to check if we are inside an transaction
@item 2 @tab Warning count
@item 1-9 @tab Message length (optional)
@item xxx @tab Message (optional)
@end multitable
Size 1-9 means that the parameter is packed in to 1-9 bytes depending on
the value. (See function sql/net_pkg.cc::net_store_length).
The message is optional. For example for multi line INSERT it
contains a string for how many rows was inserted / deleted.
@node 4.1 end packet,,,
@section 4.1 end packet
The end packet is sent as the last packet for
@itemize @bullet
@item
End of field information
@item
End of parameter type information
@item
End of result set
@end itemize
The end packet has the following structure:
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 1 @tab 254 ; Marker for EOF packet
@item 2 @tab Warning count
@item 2 @tab Status flags (For flags like SERVER_STATUS_MORE_RESULTS)
@end multitable
Note that a normal packet may start with byte 254, which means
'length stored in 9 bytes'. One can different between these cases
by checking the packet length < 9 bytes (in which case it's and end
packet).
@node 4.1 error packet
@section 4.1 error packet.
The error packet is sent when something goes wrong.
The error packet has the following structure:
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 1 @tab 255 Error packet marker
@item 2 @tab Error code
@item 1-255 @tab Null terminated error message
@end multitable
The client/server protocol is designed in such a way that a packet
can only start with 255 if it's an error packet.
@node 4.1 prep init,,,
@section 4.1 prepared statement init packet
This is the return packet when one sends a query with the COM_PREPARE
command.
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 4 @tab Statement handler id
@item 2 @tab Number of columns in result set
@item 2 @tab Number of parameters in query
@end multitable
After this, there is a packet that contains the following for each
parameter in the query:
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 2 @tab Enum value for field type. (MYSQL_TYPE_UNKNOWN if not known)
@item 2 @tab 2 byte column flags (NOT_NULL_FLAG etc)
@item 1 @tab Number of decimals
@item 4 @tab Max column length.
@end multitable
Note that the above is not yet in 4.1 but will be added this month.
As MySQL can have a parameter 'anywhere' it will in many cases not be
able to provide the optimal information for all parameters.
If number of columns, in the header packet, is not 0 then the
prepared statement will contain a result set. In this case the packet
is followed by a field description result set. @xref{4.1 field desc}.
@node 4.1 long data,,,
@section 4.1 long data handling
This is used by mysql_send_long_data() to set any parameter to a string
value. One can call mysql_send_long_data() multiple times for the
same parameter; The server will concatenate the results to a one big
string.
The server will not require an end packet for the string.
mysql_send_long_data() is responsible updating a flag that all data
has been sent. (Ie; That the last call to mysql_send_long_data() has
the 'last_data' flag set).
This packet is sent from client -> server:
@multitable @columnfractions .10 .90
@item Size @tab Comment
@item 4 @tab Statement handler
@item 2 @tab Parameter number
@item 2 @tab Type of parameter (not used at this point)
@item # @tab data (Rest of packet)
@end multitable
The server will NOT send an @code{ok} or @code{error} packet in
responce for this. If there is any errors (like to big string), one
will get the error when calling execute.
@node 4.1 execute,,,
@section 4.1 execute
On execute we send all parameters to the server in a COM_EXECUTE
packet.
The packet contains the following information:
@multitable @columnfractions .30 .70
@item Size @tab Comment
@item (param_count+9)/8 @tab Null bit map (2 bits reserved for protocol)
@item 1 @tab new_parameter_bound flag. Is set to 1 for first
execute or if one has rebound the parameters.
@item 2*param_count @tab Type of parameters (only given if new_parameter_bound flag is 1)
@item # @tab Parameter data, repeated for each parameter that are
NOT NULL and not used with mysql_send_long_data().
@end multitable
The null-bit-map is for all parameters (including parameters sent with
'mysql_send_long_data). If parameter 0 is NULL, then bit 0 in the
null-bit-map should be 1 (ie: first byte should be 1)
The parameters are stored the following ways:
@multitable @columnfractions .20 .10 .70
@item Type @tab Size @tab Comment
@item tinyint @tab 1 @tab One byte integer
@item short @tab 2 @tab
@item int @tab 4 @tab
@item longlong @tab 8 @tab
@item float @tab 4 @tab
@item double @tab 8 @tab
@item string @tab 1-9 + # @tab Packed string length + string
@end multitable
The result for this will be either an ok packet or a binary result
set.
@node 4.1 binary result,,,
@section 4.1 binary result set
A binary result are sent the following way.
For each result row:
@itemize
@item
null bit map with first two bits set to 01 (bit 0,1 value 1)
@item
parameter data, repeated for each not null result column.
@end itemize
The idea with the reserving two bits in the null map is that we can
use standard error (first byte 255) and ok packets (first byte 0)
to end a result sets.
Except that the null-bit-map is shifted two steps, the server is
sending the data to the client the same way that the server is sending
bound parameters to the client. The server is always sending the data
as type given for 'column type' for respective column. It's up to the
client to convert the parameter to the requested type.
DATETIME, DATE and TIME are sent to the server in a binary format as follows:
@multitable @columnfractions .20 .10 .70
@item Type @tab Size @tab Comment
@item date @tab 1 + 0-11 @tab Length + 2 byte year, 1 byte MMDDHHMMSS, 4 byte billionth of a second
@item datetime @tab 1 + 0-11 @tab Length + 2 byte year, 1 byte MMDDHHMMSS, 4 byte billionth of a second
@item time @tab 1 + 0-14 @tab Length + sign (0 = pos, 1= neg), 4 byte days, 1 byte HHMMDD, 4 byte billionth of a second
@end multitable
The first byte is a length byte and then comes all parameters that are
not 0. (Always counted from the beginning).
@node Fulltext Search, MyISAM Record Structure, protocol, Top
@chapter Fulltext Search in MySQL
Hopefully, sometime there will be complete description of
fulltext search algorithms.
Now it's just unsorted notes.
@menu
* Weighting in boolean mode::
@end menu
@node Weighting in boolean mode, , Fulltext Search, Fulltext Search
@section Weighting in boolean mode
The basic idea is as follows: in expression
@code{A or B or (C and D and E)}, either @code{A} or @code{B} alone
is enough to match the whole expression. While @code{C},
@code{D}, and @code{E} should @strong{all} match. So it's
reasonable to assign weight 1 to @code{A}, @code{B}, and
@code{(C and D and E)}. And @code{C}, @code{D}, and @code{E}
should get a weight of 1/3.
Things become more complicated when considering boolean
operators, as used in MySQL FTB. Obvioulsy, @code{+A +B}
should be treated as @code{A and B}, and @code{A B} -
as @code{A or B}. The problem is, that @code{+A B} can @strong{not}
be rewritten in and/or terms (that's the reason why this - extended -
set of operators was chosen). Still, aproximations can be used.
@code{+A B C} can be approximated as @code{A or (A and (B or C))}
or as @code{A or (A and B) or (A and C) or (A and B and C)}.
Applying the above logic (and omitting mathematical
transformations and normalization) one gets that for
@code{+A_1 +A_2 ... +A_N B_1 B_2 ... B_M} the weights
should be: @code{A_i = 1/N}, @code{B_j=1} if @code{N==0}, and,
otherwise, in the first rewritting approach @code{B_j = 1/3},
and in the second one - @code{B_j = (1+(M-1)*2^M)/(M*(2^(M+1)-1))}.
The second expression gives somewhat steeper increase in total
weight as number of matched B's increases, because it assigns
higher weights to individual B's. Also the first expression in
much simplier. So it is the first one, that is implemented in MySQL.
@node MyISAM Record Structure, InnoDB Record Structure, Fulltext Search, Top
@chapter MyISAM Record Structure
@section Introduction
When you say:
@*
@strong{CREATE TABLE Table1 ...}
@*
MySQL creates files named Table1.MYD ("MySQL Data"), Table1.MYI
("MySQL Index"), and Table1.FRM ("Format"). These files will be in the
directory: @*
/<datadir>/<database>/
@*
For example, if you use Linux, you might find the files here (assume
your database name is "test"): @*
/usr/local/var/test
@*
And if you use Windows, you might find the files in this directory: @*
\mysql\data\test\
@*@*
Let's look at the .MYD Data file (MyISAM SQL Data file) more closely.
@table @strong
@item Page Size
Unlike most DBMSs, MySQL doesn't store on disk using pages. Therefore
you will not see filler space between rows. (Reminder: This does not
refer to BDB and INNODB tables, which do use pages).
@*
@item Record Header
The minimal record header is a set of flags:
@itemize @bullet
@item
"X bit" = 0 if row is deleted, = 1 if row is not deleted
@item
"Null Bits" = 0 if column is not NULL, = 1 if column is NULL
@item
"Filler Bits" = 1
@end itemize
@end table
@*
Here's an example. Suppose you say:
@*
@strong{CREATE TABLE Table1 (column1 CHAR(1), column2 CHAR(1), column3 CHAR(1))}
@*
@strong{INSERT INTO Table1 VALUES ('a', 'b', 'c')}
@*
@strong{INSERT INTO Table1 VALUES ('d', NULL, 'e')}
@*
A CHAR(1) column takes precisely one byte (plus one bit of overhead
that is assigned to every column -- I'll describe the details of
column storage later). So the file Table1.MYD looks like this:
@*
@strong{Hexadecimal Display of Table1.MYD file}@*
@code{
F1 61 62 63 00 F5 64 00 66 00 ... .abc..d e.
}
@*
Here's how to read this hexadecimal-dump display:@*
@itemize @bullet
@item
The hexadecimal numbers @code{F1 61 62 63 00 F5 64 20 66 00} are byte
values and the column on the right is an attempt to show the
same bytes in ASCII.
@item
The @code{F1} byte means that there are no null fields in the first row.
@item
The @code{F5} byte means that the second column of the second row is NULL.
@end itemize
(It's probably easier to understand the flag setting if you restate
@code{F5} as @code{11110101 binary}, and (a) notice that the third flag bit from the
right is @code{on}, and (b) remember that the first flag bit is the X bit.)
@*
There are complications -- the record header is more complex if there
are variable-length fields -- but the simple display shown in the
example is exactly what you'd see if you took a debugger and looked
at the MySQL Data file.
@*
@section Physical Attributes of Columns
Next I'll describe the physical attributes of each column in a row.
The format depends entirely on the data type and the size of the
column, so, for every data type, I'll give a description and an example.
@*
@table @strong
@item The character data types
@strong{CHAR}
@itemize @bullet
@item
Storage: fixed-length string with space padding on the right.
@item
Example: a CHAR(5) column containing the value 'A' looks like:@*
@code{hexadecimal 41 20 20 20 20} -- (length = 5, value = @code{'A '})
@end itemize
@strong{VARCHAR}
@itemize @bullet
@item
Storage: variable-length string with a preceding length.
@item
Example: a VARCHAR(7) column containing 'A' looks like:@*
@code{hexadecimal 01 41} -- (length = 1, value = @code{'A'})
@end itemize
@item The numeric data types
Important: MySQL stores all multi-byte binary numbers with the
high byte first. This is called "little-endian" numeric storage;
it's normal on Intel x86 machines; MySQL uses it even for non-Intel
machines so that databases will be portable.
@*
@strong{TINYINT}
@itemize @bullet
@item
Storage: fixed-length binary, always one byte.
@item
Example: a TINYINT column containing 65 looks like:@*
@code{hexadecimal 41} -- (length = 1, value = 65)
@end itemize
@strong{SMALLINT}
@itemize @bullet
@item
Storage: fixed-length binary, always two bytes.
@item
Example: a SMALLINT column containing 65 looks like:@*
@code{hexadecimal 41 00} -- (length = 2, value = 65)
@end itemize
@strong{MEDIUMINT}
@itemize @bullet
@item
Storage: fixed-length binary, always three bytes.
@item
Example: a MEDIUMINT column containing 65 looks like:@*
@code{hexadecimal 41 00 00} -- (length = 3, value = 65)
@end itemize
@strong{INT}
@itemize @bullet
@item
Storage: fixed-length binary, always four bytes.
@item
Example: an INT column containing 65 looks like:@*
@code{hexadecimal 41 00 00 00} -- (length = 4, value = 65)
@end itemize
@strong{BIGINT}
@itemize @bullet
@item
Storage: fixed-length binary, always eight bytes.
@item
Example: a BIGINT column containing 65 looks like:@*
@code{hexadecimal 41 00 00 00 00 00 00 00} -- (length = 8, value = 65)
@end itemize
@strong{FLOAT}
@itemize @bullet
@item
Storage: fixed-length binary, always four bytes.
@item
Example: a FLOAT column containing approximately 65 looks like:@*
@code{hexadecimal 00 00 82 42} -- (length = 4, value = 65)
@end itemize
@strong{DOUBLE PRECISION}
@itemize @bullet
@item
Storage: fixed-length binary, always eight bytes.
@item
Example: a DOUBLE PRECISION column containing approximately 65 looks like:@*
@code{hexadecimal 00 00 00 00 00 40 50 40} -- (length = 8, value = 65)
@end itemize
@strong{REAL}
@itemize @bullet
@item
Storage: same as FLOAT, or same as DOUBLE PRECISION, depending on setting of the --ansi switch.
@end itemize
@strong{DECIMAL}
@itemize @bullet
@item
Storage: fixed-length string, with a leading byte for the sign, if any.
@item
Example: a DECIMAL(2) column containing 65 looks like:@*
@code{hexadecimal 20 36 35} -- (length = 3, value = @code{' 65'})
@item
Example: a DECIMAL(2) UNSIGNED column containing 65 looks like:@*
@code{hexadecimal 36 35} -- (length = 2, value = @code{'65'})
@item
Example: a DECIMAL(4,2) UNSIGNED column containing 65 looks like:@*
@code{hexadecimal 36 35 2E 30 30} -- (length = 5, value = @code{'65.00'})
@end itemize
@strong{NUMERIC}
@itemize @bullet
@item
Storage: same as DECIMAL.
@end itemize
@strong{BOOL}
@itemize @bullet
@item
Storage: same as TINYINT.
@end itemize
@item The temporal data types
@strong{DATE}
@itemize @bullet
@item
Storage: 3 byte integer, low byte first.
Packed as: 'day + month*32 + year*16*32'
@item
Example: a DATE column containing '1962-01-02' looks like:@*
@code{hexadecimal 22 54 0F}
@end itemize
@strong{DATETIME}
@itemize @bullet
@item
Storage: eight bytes.
@item
Part 1 is a 32-bit integer containing year*10000 + month*100 + day.
@item
Part 2 is a 32-bit integer containing hour*10000 + minute*100 + second.
@item
Example: a DATETIME column for '0001-01-01 01:01:01' looks like:@*
@code{hexadecimal B5 2E 11 5A 02 00 00 00}
@end itemize
@strong{TIME}
@itemize @bullet
@item
Storage: 3 bytes, low byte first.
This is stored as seconds: days*24*3600+hours*3600+minutes*60+seconds
@item
Example: a TIME column containing '1 02:03:04' (1 day 2 hour 3 minutes and 4 seconds) looks like:@*
@code{hexadecimal 58 6E 01}
@end itemize
@strong{TIMESTAMP}
@itemize @bullet
@item
Storage: 4 bytes, low byte first.
Stored as unix @code{time()}, which is seconds since the Epoch
(00:00:00 UTC, January 1, 1970).
@item
Example: a TIMESTAMP column containing '2003-01-01 01:01:01' looks like:@*
@code{hexadecimal 4D AE 12 23}
@end itemize
@strong{YEAR}
@itemize @bullet
@item
Storage: same as unsigned TINYINT with a base value of 0 = 1901.
@end itemize
@item Others
@strong{SET}
@itemize @bullet
@item
Storage: one byte for each eight members in the set.
@item
Maximum length: eight bytes (for maximum 64 members).
@item
This is a bit list. The least significant bit corresponds to the
first listed member of the set.
@item
Example: a SET('A','B','C') column containing 'A' looks like:@*
@code{01} -- (length = 1, value = 'A')
@end itemize
@strong{ENUM}
@itemize @bullet
@item
Storage: one byte if less than 256 alternatives, else two bytes.
@item
This is an index. The value 1 corresponds to the first listed
alternative. (Note: ENUM always reserves 0 for a blank '' value. This
explains why 'A' is 1 instead of 0.)
@item
Example: an ENUM('A','B','C') column containing 'A' looks like:@*
@code{01} -- (length = 1, value = 'A')
@end itemize
@item The Large-Object data types
Warning: Because TINYBLOB's preceding length is one byte long (the
size of a TINYINT) and MEDIUMBLOB's preceding length is three bytes
long (the size of a MEDIUMINT), it's easy to think there's some sort
of correspondence between the BLOB and the INT types. There isn't -- a
BLOB's preceding length is not four bytes long (the size of an INT).
@*
(NOTE TO SELF: BLOB storage has not been fully addressed here.)
@*
@strong{TINYBLOB}
@itemize @bullet
@item
Storage: variable-length string with a preceding one-byte length.
@item
Example: a TINYBLOB column containing 'A' looks like:@*
@code{hexadecimal 01 41} -- (length = 2, value = 'A')
@end itemize
@strong{TINYTEXT}
@itemize @bullet
@item
Storage: same as TINYBLOB.
@end itemize
@strong{BLOB}
@itemize @bullet
@item
Storage: variable-length string with a preceding two-byte length.
@item
Example: a BLOB column containing 'A' looks like:@*
@code{hexadecimal 01 00 41} -- (length = 2, value = 'A')
@end itemize
@strong{TEXT}
@itemize @bullet
@item
Storage: same as BLOB.
@end itemize
@strong{MEDIUMBLOB}
@itemize @bullet
@item
Storage: variable-length string with a preceding length.
@item
Example: a MEDIUMBLOB column containing 'A' looks like:@*
@code{hexadecimal 01 00 00 41} -- (length = 4, value = 'A')
@end itemize
@strong{MEDIUMTEXT}
@itemize @bullet
@item
Storage: same as MEDIUMBLOB.
@end itemize
@strong{LONGBLOB}
@itemize @bullet
@item
Storage: variable-length string with a preceding four-byte length.
@item
Example: a LONGBLOB column containing 'A' looks like:@*
@code{hexadecimal 01 00 00 00 41} -- (length = 5, value = 'A')
@end itemize
@strong{LONGTEXT}
@itemize @bullet
@item
Storage: same as LONGBLOB.
@end itemize
@end table
@section Where to Look For More Information
@strong{References:} @*
Most of the formatting work for MyISAM columns is visible
in the program /sql/field.cc in the source code directory.
@*
@node InnoDB Record Structure,InnoDB Page Structure,MyISAM Record Structure,Top
@chapter InnoDB Record Structure
This page contains:
@itemize @bullet
@item
A high-altitude "summary" picture of the parts of a MySQL/InnoDB
record structure.
@item
A description of each part.
@item
An example.
@end itemize
After reading this page, you will know how MySQL/InnoDB stores a
physical record.
@*
@section High-Altitude Picture
The chart below shows the three parts of a physical record.
@multitable @columnfractions .10 .35
@item @strong{Name} @tab @strong{Size}
@item Field Start Offsets
@tab (F*1) or (F*2) bytes
@item Extra Bytes
@tab 6 bytes
@item Field Contents
@tab depends on content
@end multitable
Legend: The letter 'F' stands for 'Number Of Fields'.
The meaning of the parts is as follows:
@itemize @bullet
@item
The FIELD START OFFSETS is a list of numbers containing the
information "where a field starts".
@item
The EXTRA BYTES is a fixed-size header.
@item
The FIELD CONTENTS contains the actual data.
@end itemize
@strong{An Important Note About The Word "Origin"}@*
The "Origin" or "Zero Point" of a record is the first byte of the
Field Contents -- not the first byte of the Field Start Offsets. If
there is a pointer to a record, that pointer is pointing to the
Origin. Therefore the first two parts of the record are addressed by
subtracting from the pointer, and only the third part is addressed by
adding to the pointer.
@subsection FIELD START OFFSETS
The Field Start Offsets is a list in which each entry is the
position, relative to the Origin, of the start of the next field. The
entries are in reverse order, that is, the first field's offset is at
the end of the list.
@*
An example: suppose there are three columns. The first column's length
is 1, the second column's length is 2, and the third column's length is 4.
In this case, the offset values are, respectively, 1, 3 (1+2), and 7 (1+2+4).
Because values are reversed, a core dump of the Field Start Offsets
would look like this: @code{07,03,01}.
@*
There are two complications for special cases:
@itemize @bullet
@item
Complication #1: The size of each offset can be either one byte or
two bytes. One-byte offsets are only usable if the total record size
is less than 127. There is a flag in the "Extra Bytes" part which will
tell you whether the size is one byte or two bytes.
@item
Complication #2: The most significant bits of an offset may contain
flag values. The next two paragraphs explain what the contents are.
@end itemize
@strong{When The Size Of Each Offset Is One Byte}
@itemize @bullet
@item
1 bit = 0 if field is non-NULL, = 1 if field is NULL
@item
7 bits = the actual offset, a number between 0 and 127
@end itemize
@strong{When The Size Of Each Offset Is Two Bytes}
@itemize @bullet
@item
1 bit = 0 if field is non-NULL, = 1 if field is NULL
@item
1 bit = 0 if field is on same page as offset, = 1 if field and offset are on different pages
@item
14 bits = the actual offset, a number between 0 and 16383
@end itemize
It is unlikely that the "field and offset are on different pages"
unless the record contains a large BLOB.
@subsection EXTRA BYTES
The Extra Bytes are a fixed six-byte header.
@multitable @columnfractions .10 .25 .35
@item @strong{Name} @tab @strong{Size} @tab @strong{Description}
@item @strong{info_bits:}
@item ()
@tab 1 bit
@tab unused or unknown
@item ()
@tab 1 bit
@tab unused or unknown
@item deleted_flag
@tab 1 bit
@tab 1 if record is deleted
@item min_rec_flag
@tab 1 bit
@tab 1 if record is predefined minimum record
@item n_owned
@tab 4 bits
@tab number of records owned by this record
@item heap_no
@tab 13 bits
@tab record's order number in heap of index page
@item n_fields
@tab 10 bits
@tab number of fields in this record, 1 to 1023
@item 1byte_offs_flag
@tab 1 bit
@tab 1 if each Field Start Offsets is 1 byte long (this item is also called the "short" flag)
@item @strong{next 16 bits}
@tab 16 bits
@tab pointer to next record in page
@item @strong{TOTAL}
@tab 48 bits
@end multitable
Total size is 48 bits, which is six bytes.
@*
If you're just trying to read the record, the key bit in the Extra
Bytes is 1byte_offs_flag -- you need to know if 1byte_offs_flag is 1
(i.e.: "short 1-byteoffsets") or 0 (i.e.: "2-byte offsets").
@*
Given a pointer to the Origin, InnoDB finds the start of the record as follows:
@itemize @bullet
@item
Let X = n_fields (the number of fields is by definition equal to the
number of entries in the Field Start Offsets Table).
@item
If 1byte_offs_flag equals 0, then let X = X * 2 because there are
two bytes for each entry instead of just one.
@item
Let X = X + 6, because the fixed size of Extra Bytes is 6.
@item
The start of the record is at (pointer value minus X).
@end itemize
@subsection FIELD CONTENTS
The Field Contents part of the record has all the data. Fields are
stored in the order they were defined in.
@*
There are no markers between fields, and there is no marker or filler
at the end of a record.
@*
Here's an example.
@itemize @bullet
@item
I made a table with this definition:
@*@*
@strong{CREATE TABLE T
(FIELD1 VARCHAR(3), FIELD2 VARCHAR(3), FIELD3 VARCHAR(3))
Type=InnoDB;}
@*@*
To understand what follows, you must know that table T has six columns
-- not three -- because InnoDB automatically added three "system
columns" at the start for its own housekeeping. It happens that these
system columns are the row ID, the transaction ID, and the rollback
pointer, but their values don't matter now. Regard them as three black
boxes.
@*@*
@item
I put some rows in the table. My last three INSERTs were:
@*@*
@strong{INSERT INTO T VALUES ('PP', 'PP', 'PP')}
@*@*
@strong{INSERT INTO T VALUES ('Q', 'Q', 'Q')}
@*@*
@strong{INSERT INTO T VALUES ('R', NULL, NULL)}
@*@*
@item
I ran Borland's TDUMP to get a hexadecimal dump of
the contents of \mysql\data\ibdata1, which (in my case) is the
MySQL/InnoDB data file (on Windows).
@end itemize
Here is an extract of the dump:
@multitable @columnfractions .05 .95
@item @strong{Address Values In Hexadecimal} @tab @strong{Values In ASCII}
@item @code{0D4280: 00 00 2D 00 84 4F 4F 4F 4F 4F 4F 4F 4F 4F 19 17}
@tab @code{..-..OOOOOOOOO..}
@item @code{0D4290: 15 13 0C 06 00 00 78 0D 02 BF 00 00 00 00 04 21}
@tab @code{......x........!}
@item @code{0D42A0: 00 00 00 00 09 2A 80 00 00 00 2D 00 84 50 50 50}
@tab @code{.....*....-..PPP}
@item @code{0D42B0: 50 50 50 16 15 14 13 0C 06 00 00 80 0D 02 E1 00}
@tab @code{PPP.............}
@item @code{0D42C0: 00 00 00 04 22 00 00 00 00 09 2B 80 00 00 00 2D}
@tab @code{....".....+....-}
@item @code{0D42D0: 00 84 51 51 51 94 94 14 13 0C 06 00 00 88 0D 00}
@tab @code{..QQQ...........}
@item @code{0D42E0: 74 00 00 00 00 04 23 00 00 00 00 09 2C 80 00 00}
@tab @code{t.....#.....,...}
@item @code{0D42F0: 00 2D 00 84 52 00 00 00 00 00 00 00 00 00 00 00}
@tab @code{.-..R...........}
@end multitable
A reformatted version of the dump, showing only the relevant bytes,
looks like this (I've put a line break after each field and added labels):
@strong{Reformatted Hexadecimal Dump}@*
@code{
19 17 15 13 0C 06 Field Start Offsets /* First Row */@*
00 00 78 0D 02 BF Extra Bytes@*
00 00 00 00 04 21 System Column #1@*
00 00 00 00 09 2A System Column #2@*
80 00 00 00 2D 00 84 System Column #3@*
50 50 Field1 'PP'@*
50 50 Field2 'PP'@*
50 50 Field3 'PP'}@*
@code{
16 15 14 13 0C 06 Field Start Offsets /* Second Row */@*
00 00 80 0D 02 E1 Extra Bytes@*
00 00 00 00 04 22 System Column #1@*
00 00 00 00 09 2B 80 System Column #2@*
00 00 00 2D 00 84 System Column #3@*
51 Field1 'Q'@*
51 Field2 'Q'@*
51 Field3 'Q'}@*
@code{
94 94 14 13 0C 06 Field Start Offsets /* Third Row */@*
00 00 88 0D 00 74 Extra Bytes@*
00 00 00 00 04 23 System Column #1@*
00 00 00 00 09 2C System Column #2@*
80 00 00 00 2D 00 84 System Column #3@*
52 Field1 'R'}@*
@*
You won't need explanation if you followed everything I've said, but
I'll add helpful notes for the three trickiest details.
@itemize @bullet
@item
Helpful Notes About "Field Start Offsets": @*
Notice that the sizes of the record's fields, in forward order, are:
6, 6, 7, 2, 2, 2. Since each offset is for the start of the "next"
field, the hexadecimal offsets are 06, 0c (6+6), 13 (6+6+7), 15
(6+6+7+2), 17 (6+6+7+2+2), 19 (6+6+7+2+2+2). Reversing the order, the
Field Start Offsets of the first record are: @code{19,17,15,13,0c,06}.
@item
Helpful Notes About "Extra Bytes": @*
Look at the Extra Bytes of the first record: @code{00 00 78 0D 02 BF}. The
fourth byte is @code{0D hexadecimal}, which is @code{1101 binary} ... the 110 is the
last bits of n_fields (@code{110 binary} is 6 which is indeed the number of
fields in the record) and the final 1 bit is 1byte_offs_flag. The
fifth and sixth bytes, which contain @code{02 BF}, constitute the "next"
field. Looking at the original hexadecimal dump, at address
@code{0D42BF} (which is position @code{02BF} within the page), you'll see the beginning bytes of
System Column #1 of the second row. In other words, the "next" field
points to the "Origin" of the following row.
@item
Helpful Notes About NULLs:@*
For the third row, I inserted NULLs in FIELD2 and FIELD3. Therefore in
the Field Start Offsets the top bit is @code{on} for these fields (the
values are @code{94 hexadecimal}, @code{94 hexadecimal}, instead of
@code{14 hexadecimal}, @code{14 hexadecimal}). And the row is
shorter because the NULLs take no space.
@end itemize
@section Where to Look For More Information
@strong{References:} @*
The most relevant InnoDB source-code files are rem0rec.c, rem0rec.ic,
and rem0rec.h in the rem ("Record Manager") directory.
@node InnoDB Page Structure,Files in MySQL Sources,InnoDB Record Structure,Top
@chapter InnoDB Page Structure
InnoDB stores all records inside a fixed-size unit which is commonly called a
"page" (though InnoDB sometimes calls it a "block" instead).
Currently all pages are the same size, 16KB.
@*
A page contains records, but it also contains headers and trailers.
I'll start this description with a high-altitude view of a page's parts,
then I'll describe each part of a page. Finally, I'll show an example. This
discussion deals only with the most common format, for the leaf page of a data file.
@*
@section High-Altitude View
An InnoDB page has seven parts:
@itemize @bullet
@item
Fil Header
@item
Page Header
@item
Infimum + Supremum Records
@item
User Records
@item
Free Space
@item
Page Directory
@item
Fil Trailer
@end itemize
As you can see, a page has two header/trailer pairs. The inner pair, "Page Header" and
"Page Directory", are mostly the concern of the \page program group,
while the outer pair, "Fil Header" and "Fil Trailer", are mostly the
concern of the \fil program group. The "Fil" header also goes goes by
the name of "File Page Header".
@*
Sandwiched between the headers and trailers, are the records and
the free (unused) space. A page always begins with two unchanging
records called the Infimum and the Supremum. Then come the user
records. Between the user records (which grow downwards) and the page
directory (which grows upwards) there is space for new records.
@*
@subsection Fil Header
The Fil Header has eight parts, as follows:
@multitable @columnfractions .10 .30 .35
@item @strong{Name} @tab @strong{Size} @tab @strong{Remarks}
@item FIL_PAGE_SPACE
@tab 4
@tab 4 ID of the space the page is in
@item FIL_PAGE_OFFSET
@tab 4
@tab ordinal page number from start of space
@item FIL_PAGE_PREV
@tab 4
@tab offset of previous page in key order
@item FIL_PAGE_NEXT
@tab 4
@tab offset of next page in key order
@item FIL_PAGE_LSN
@tab 8
@tab log serial number of page's latest log record
@item FIL_PAGE_TYPE
@tab 2
@tab current defined types are: FIL_PAGE_INDEX, FIL_PAGE_UNDO_LOG, FIL_PAGE_INODE, FIL_PAGE_IBUF_FREE_LIST
@item FIL_PAGE_FILE_FLUSH_LSN
@tab 8
@tab "the file has been flushed to disk at least up to this lsn" (log serial number),
valid only on the first page of the file
@item FIL_PAGE_ARCH_LOG_NO
@tab 4
@tab the latest archived log file number at the time that FIL_PAGE_FILE_FLUSH_LSN was written (in the log)
@end multitable
@itemize
@item
FIL_PAGE_SPACE is a necessary identifier because different pages might belong to
different (table) spaces within the same file. The word
"space" is generic jargon for either "log" or "tablespace".
@*@*
@item
FIL_PAGE_PREV and FIL_PAGE_NEXT are the page's "backward" and
"forward" pointers. To show what they're about, I'll draw a two-level
B-tree.
@*@*
@example
--------
- root -
--------
|
----------------------
| |
| |
-------- --------
- leaf - <--> - leaf -
-------- --------
@end example
@*
Everyone has seen a B-tree and knows that the entries in the root page
point to the leaf pages. (I indicate those pointers with vertical '|'
bars in the drawing.) But sometimes people miss the detail that leaf
pages can also point to each other (I indicate those pointers with a horizontal
two-way pointer '<-->' in the drawing). This feature allows InnoDB to navigate from
leaf to leaf without having to back up to the root level. This is a
sophistication which you won't find in the classic B-tree, which is
why InnoDB should perhaps be called a B+-tree instead.
@*@*
@item
The fields FIL_PAGE_FILE_FLUSH_LSN, FIL_PAGE_PREV, and FIL_PAGE_NEXT
all have to do with logs, so I'll refer you to my article "How Logs
Work With MySQL And InnoDB" on devarticles.com.
@*@*
@item
FIL_PAGE_FILE_FLUSH_LSN and FIL_PAGE_ARCH_LOG_NO are only valid for
the first page of a data file.
@end itemize
@subsection Page Header
The Page Header has 14 parts, as follows:
@*@*
@multitable @columnfractions .10 .20 .30
@item @strong{Name} @tab @strong{Size} @tab @strong{Remarks}
@item PAGE_N_DIR_SLOTS
@tab 2
@tab number of directory slots in the Page Directory part; initial value = 2
@item PAGE_HEAP_TOP
@tab 2
@tab record pointer to first record in heap
@item PAGE_N_HEAP
@tab 2
@tab number of heap records; initial value = 2
@item PAGE_FREE
@tab 2
@tab record pointer to first free record
@item PAGE_GARBAGE
@tab 2
@tab "number of bytes in deleted records"
@item PAGE_LAST_INSERT
@tab 2
@tab record pointer to the last inserted record
@item PAGE_DIRECTION
@tab 2
@tab either PAGE_LEFT, PAGE_RIGHT, or PAGE_NO_DIRECTION
@item PAGE_N_DIRECTION
@tab 2
@tab number of consecutive inserts in the same direction, e.g. "last 5 were all to the left"
@item PAGE_N_RECS
@tab 2
@tab number of user records
@item PAGE_MAX_TRX_ID
@tab 8
@tab the highest ID of a transaction which might have changed a record on the page (only set for secondary indexes)
@item PAGE_LEVEL
@tab 2
@tab level within the index (0 for a leaf page)
@item PAGE_INDEX_ID
@tab 8
@tab identifier of the index the page belongs to
@item PAGE_BTR_SEG_LEAF
@tab 10
@tab "file segment header for the leaf pages in a B-tree" (this is irrelevant here)
@item PAGE_BTR_SEG_TOP
@tab 10
@tab "file segment header for the non-leaf pages in a B-tree" (this is irrelevant here)
@end multitable
@*
(Note: I'll clarify what a "heap" is when I discuss the User Records part of the page.)
@*@*
Some of the Page Header parts require further explanation:
@itemize @bullet
@item
PAGE_FREE: @*
Records which have been freed (due to deletion or migration) are in a
one-way linked list. The PAGE_FREE pointer in the page header points
to the first record in the list. The "next" pointer in the record
header (specifically, in the record's Extra Bytes) points to the next
record in the list.
@item
PAGE_DIRECTION and PAGE_N_DIRECTION: @*
It's useful to know whether inserts are coming in a constantly
ascending sequence. That can affect InnoDB's efficiency.
@item
PAGE_HEAP_TOP and PAGE_FREE and PAGE_LAST_INSERT: @*
Warning: Like all record pointers, these point not to the beginning of the
record but to its Origin (see the earlier discussion of Record
Structure).
@item
PAGE_BTR_SEG_LEAF and PAGE_BTR_SEG_TOP: @*
These variables contain information (space ID, page number, and byte offset) about
index node file segments. InnoDB uses the information for allocating new pages.
There are two different variables because InnoDB allocates separately for leaf
pages and upper-level pages.
@end itemize
@subsection The Infimum And Supremum Records
"Infimum" and "supremum" are real English words but they are found
only in arcane mathematical treatises, and in InnoDB comments. To
InnoDB, an infimum is lower than the the lowest possible real value
(negative infinity) and a supremum is greater than the greatest
possible real value (positive infinity). InnoDB sets up an infimum
record and a supremum record automatically at page-create time, and
never deletes them. They make a useful barrier to navigation so that
"get-prev" won't pass the beginning and "get-next" won't pass the end.
Also, the infimum record can be a dummy target for temporary record
locks.
@*@*
The InnoDB code comments distinguish between "the infimum and supremum
records" and the "user records" (all other kinds).
@*@*
It's sometimes unclear whether InnoDB considers the infimum and
supremum to be part of the header or not. Their size is fixed and
their position is fixed, so I guess so.
@subsection User Records
In the User Records part of a page, you'll find all the records that the user
inserted.
@*@*
There are two ways to navigate through the user records, depending
whether you want to think of their organization as an unordered or an
ordered list.
@*@*
An unordered list is often called a "heap". If you make a pile of
stones by saying "whichever one I happen to pick up next will go on
top" -- rather than organizing them according to size and colour --
then you end up with a heap. Similarly, InnoDB does not want to insert
new rows according to the B-tree's key order (that would involve
expensive shifting of large amounts of data), so it inserts new rows
right after the end of the existing rows (at the
top of the Free Space part) or wherever there's space left by a
deleted row.
@*@*
But by definition the records of a B-tree must be accessible in order
by key value, so there is a record pointer in each record (the "next"
field in the Extra Bytes) which points to the next record in key
order. In other words, the records are a one-way linked list. So
InnoDB can access rows in key order when searching.
@subsection Free Space
I think it's clear what the Free Space part of a page is, from the discussion of
other parts.
@subsection Page Directory
The Page Directory part of a page has a variable number of record pointers.
Sometimes the record pointers are called "slots" or "directory slots".
Unlike other DBMSs, InnoDB does not have a slot for every record in
the page. Instead it keeps a sparse directory. In a fullish page,
there will be one slot for every six records.
@*@*
The slots track the records' logical order (the order by key rather
than the order by placement on the heap). Therefore, if the records
are @code{'A' 'B' 'F' 'D'} the slots will be @code{(pointer to 'A') (pointer to
'B') (pointer to 'D') (pointer to 'F')}. Because the slots are in key
order, and each slot has a fixed size, it's easy to do a binary
search of the records on the page via the slots.
@*@*
(Since the Page Directory does not have a slot for every record,
binary search can only give a rough position and then InnoDB must
follow the "next" record pointers. InnoDB's "sparse slots" policy also
accounts for the n_owned field in the Extra Bytes part of a record:
n_owned indicates how many more records must be gone through because
they don't have their own slots.)
@subsection Fil Trailer
The Fil Trailer has one part, as follows:
@*@*
@multitable @columnfractions .10 .35 .40
@item @strong{Name} @tab @strong{Size} @tab @strong{Remarks}
@item FIL_PAGE_END_LSN
@tab 8
@tab low 4 bytes = checksum of page, last 4 bytes = same as FIL_PAGE_LSN
@end multitable
@*
The final part of a page, the fil trailer (or File Page Trailer),
exists because InnoDB's architect worried about integrity. It's
impossible for a page to be only half-written, or corrupted by
crashes, because the log-recovery mechanism restores to a consistent
state. But if something goes really wrong, then it's nice to have a
checksum, and to have a value at the very end of the page which must
be the same as a value at the very beginning of the page.
@section Example
For this example, I used Borland's TDUMP again, as I did for the earlier chapter on
Record Format. This is what a page looked like:
@*@*
@multitable @columnfractions .05 .95
@item @strong{Address Values In Hexadecimal} @tab @strong{Values In ASCII}
@item @code{0D4000: 00 00 00 00 00 00 00 35 FF FF FF FF FF FF FF FF}
@tab @code{.......5........}
@item @code{0D4010: 00 00 00 00 00 00 E2 64 45 BF 00 00 00 00 00 00}
@tab @code{.......dE.......}
@item @code{0D4020: 00 00 00 00 00 00 00 05 02 F5 00 12 00 00 00 00}
@tab @code{................}
@item @code{0D4030: 02 E1 00 02 00 0F 00 10 00 00 00 00 00 00 00 00}
@tab @code{................}
@item @code{0D4040: 00 00 00 00 00 00 00 00 00 14 00 00 00 00 00 00}
@tab @code{................}
@item @code{0D4050: 00 02 16 B2 00 00 00 00 00 00 00 02 15 F2 08 01}
@tab @code{................}
@item @code{0D4060: 00 00 03 00 89 69 6E 66 69 6D 75 6D 00 09 05 00}
@tab @code{.....infimum....}
@item @code{0D4070: 08 03 00 00 73 75 70 72 65 6D 75 6D 00 22 1D 18}
@tab @code{....supremum."..}
@item @code{0D4080: 13 0C 06 00 00 10 0D 00 B7 00 00 00 00 04 14 00}
@tab @code{................}
@item @code{0D4090: 00 00 00 09 1D 80 00 00 00 2D 00 84 41 41 41 41}
@tab @code{.........-..AAAA}
@item @code{0D40A0: 41 41 41 41 41 41 41 41 41 41 41 1F 1B 17 13 0C}
@tab @code{AAAAAAAAAAA.....}
@item @code{ ... }
@item @code{ ... }
@item @code{0D7FE0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 74}
@tab @code{...............t}
@item @code{0D7FF0: 02 47 01 AA 01 0A 00 65 3A E0 AA 71 00 00 E2 64}
@tab @code{.G.....e:..q...d}
@end multitable
@*@*
Let's skip past the first 38 bytes, which are Fil Header. The bytes
of the Page Header start at location @code{0d4026 hexadecimal}:
@*@*
@multitable @columnfractions .10 .45 .60
@item @strong{Location} @tab @strong{Name} @tab @strong{Description}
@item @code{00 05}
@tab PAGE_N_DIR_SLOTS
@tab There are 5 directory slots.
@item @code{02 F5}
@tab PAGE_HEAP_TOP
@tab At location @code{0402F5}, not shown, is the beginning of free space.
Maybe a better name would have been PAGE_HEAP_END
@item @code{00 12}
@tab PAGE_N_HEAP
@tab There are 18 (hexadecimal 12) records in the page.
@item @code{00 00}
@tab PAGE_FREE
@tab There are zero free (deleted) records.
@item @code{00 00}
@tab PAGE_GARBAGE
@tab There are zero bytes in deleted records.
@item @code{02 E1}
@tab PAGE_LAST_INSERT
@tab The last record was inserted at location @code{02E1}, not shown, within the page.
@item @code{00 02}
@tab PAGE_DIRECTION
@tab A glance at page0page.h will tell you that 2 is the #defined value for PAGE_RIGHT.
@item @code{00 0F}
@tab PAGE_N_DIRECTION
@tab The last 15 (hexadecimal 0F) inserts were all done "to the right"
because I was inserting in ascending order.
@item @code{00 10}
@tab PAGE_N_RECS
@tab There are 16 (hexadecimal 10) user records. Notice that PAGE_N_RECS is
smaller than the earlier field, PAGE_N_HEAP.
@item @code{00 00 00 00 00 00 00}
@tab PAGE_MAX_TRX_ID
@item @code{00 00}
@tab PAGE_LEVEL
@tab Zero because this is a leaf page.
@item @code{00 00 00 00 00 00 00 14}
@tab PAGE_INDEX_ID
@tab This is index number 20.
@item @code{00 00 00 00 00 00 00 02 16 B2}
@tab PAGE_BTR_SEG_LEAF
@item @code{00 00 00 00 00 00 00 02 15 F2}
@tab PAGE_BTR_SEG_TOP
@end multitable
@*
Immediately after the page header are the infimum and supremum
records. Looking at the "Values In ASCII" column in the hexadecimal
dump, you will see that the contents are in fact the words "infimum"
and "supremum" respectively.
@*@*
Skipping past the User Records and the Free Space, many bytes later,
is the end of the 16KB page. The values shown there are the two trailers.
@itemize @bullet
@item
The first trailer (@code{00 74, 02 47, 01 AA, 01 0A, 00 65}) is the page
directory. It has 5 entries, because the header field PAGE_N_DIR_SLOTS
says there are 5.
@item
The next trailer (@code{3A E0 AA 71, 00 00 E2 64}) is the fil trailer. Notice
that the last four bytes, @code{00 00 E2 64}, appeared before in the fil
header.
@end itemize
@section Where to Look For More Information
@strong{References:} @*
The most relevant InnoDB source-code files are page0page.c,
page0page.ic, and page0page.h in \page directory.
@node Files in MySQL Sources,Files in InnoDB Sources,InnoDB Page Structure,Top
@chapter Annotated List Of Files in the MySQL Source Code Distribution
This is a description of the files that you get when you download the
source code of MySQL. This description begins with a list
of the 43 directories and a short comment about each one. Then, for
each directory, in alphabetical order, a longer description is
supplied. When a directory contains significant program files, a list of each C
program is given along with an explanation of its intended function.
@section Directory Listing
@strong{Directory -- Short Comment}
@itemize @bullet
@item
bdb -- The Berkeley Database table handler
@item
BitKeeper -- BitKeeper administration
@item
BUILD -- Build switches
@item
Build-tools -- Build tools
@item
client -- Client library
@item
cmd-line-utils -- Command-line utilities
@item
dbug -- Fred Fish's dbug library
@item
div -- Deadlock test
@item
Docs -- Preliminary documents about internals and new modules
@item
extra -- Eight minor standalone utility programs
@item
fs -- File System
@item
heap -- The HEAP table handler
@item
Images -- Empty directory
@item
include -- Include (*.h) files
@item
innobase -- The Innobase (InnoDB) table handler
@item
isam -- The ISAM (MySQL) table handler
@item
libmysql -- For producing MySQL as a library (e.g. a Windows DLL)
@item
libmysql_r -- Only one file, a makefile
@item
libmysqld -- The MySQL Library
@item
man -- Manual pages
@item
merge -- The MERGE table handler (see Reference Manual section 7.2)
@item
myisam -- The MyISAM table handler
@item
myisammrg -- The MyISAM Merge table handler
@item
mysql-test -- A test suite for mysqld
@item
mysys -- MySQL system library (Low level routines for file access
etc.)
@item
netware -- Files related to the Novell NetWare version of MySQL
@item
NEW-RPMS -- New "RPM Package Manager" files
@item
os2 -- Routines for working with the OS/2 operating system
@item
pstack -- Process stack display
@item
regex -- Regular Expression library for support of REGEXP function
@item
repl-tests -- Test cases for replication
@item
SCCS -- Source Code Control System
@item
scripts -- SQL batches, e.g. for converting msql to MySQL
@item
sql -- Programs for handling SQL commands. The "core" of MySQL
@item
sql-bench -- The MySQL benchmarks
@item
SSL -- Secure Sockets Layer
@item
strings -- Library for C string routines, e.g. atof, strchr
@item
support-files -- 15 files used for building, containing switches?
@item
tests -- Tests in Perl
@item
tools -- mysqlmanager.c
@item
VC++Files -- Includes this entire directory, repeated for VC++
(Windows) use
@item
vio -- Virtual I/O Library
@item
zlib -- data compression library
@end itemize
@subsection bdb
The Berkeley Database table handler.
@*@*
The Berkeley Database (BDB) is maintained by Sleepycat Software.
@*@*
The documentation for BDB is available at
http://www.sleepycat.com/docs/. Since it's reasonably thorough
documentation, a description of the BDB program files is not included
in this document.
@*@*
@subsection BitKeeper
BitKeeper administration.
@*@*
This directory may be present if you downloaded the MySQL source using
BitKeeper rather than via the mysql.com site. The files in the
BitKeeper directory are for maintenance purposes only -- they are not
part of the MySQL package.
@*@*
@subsection BUILD
Build switches.
@*@*
This directory contains the build switches for compilation on various
platforms. There is a subdirectory for each set of options. The main
ones are:
@itemize @bullet
@item
alpha
@item
ia64
@item
pentium (with and without debug or bdb, etc.)
@item
solaris
@end itemize
@*@*
@subsection Build-tools
Build tools.
@*@*
This directory contains batch files for extracting, making
directories, and making programs from source files. There are several
subdirectories -- for building Linux executables, for compiling, for
performing all build steps, etc.
@*@*
@subsection client
Client library.
@*@*
The client library includes mysql.cc (the source of the 'mysql'
executable) and other utilities. Most of the utilities are mentioned
in the MySQL Reference Manual. Generally these are standalone C
programs which one runs in "client mode", that is, they call the
server.
@*@*
The C program files in the directory are:
@itemize @bullet
@item
connect_test.c -- test that a connect is possible
@item
get_password.c -- ask for a password from the console
@item
insert_test.c -- test that an insert is possible
@item
list_test.c -- test that a select is possible
@item
mysql.cc -- "The MySQL command tool"
@item
mysqladmin.c -- maintenance of MYSQL databases
@item
mysqlcheck.c -- check all databases, check connect, etc.
@item
mysqldump.c -- dump table's contents in ascii
@item
mysqlimport.c -- import file into a table
@item
mysqlmanager-pwgen.c -- pwgen seems to stand for "password
generation"
@item
mysqlmanagerc.c -- entry point for mysql manager
@item
mysqlshow.c -- show databases, tables or columns
@item
mysqltest.c -- test program
@item
password.c -- password checking routines
@item
select_test.c -- test that a select is possible
@item
showdb_test.c -- test that a show-databases is possible
@item
ssl_test.c -- test that SSL is possible
@item
thread_test.c -- test that threading is possible
@end itemize
@*@*
@subsection cmd-line-utils
Command-line utilities.
@*@*
There are two subdirectories: \readline and \libedit. All the files
here are "non-MYSQL" files, in the sense that MySQL AB didn't produce
them, it just uses them. It should be unnecessary to study the
programs in these files unless
you are writing or debugging a tty-like client for MySQL, such as
mysql.exe.
@*@*
The \readline subdirectory contains the files of the GNU Readline
Library, "a library for reading lines of text with interactive input
and history editing". The programs are copyrighted by the Free
Software Foundation.
@*@*
The \libedit (library of edit functions) subdirectory has files
written by Christos Zoulas. They are for editing the line contents.
These are the program files in the \libedit subdirectory:
@itemize @bullet
@item
chared.c -- character editor
@item
common.c -- common editor functions
@item
el.c -- editline interface functions
@item
emacs.c -- emacs functions
@item
fgetln.c -- get line
@item
hist.c -- history access functions
@item
history.c -- more history access functions
@item
key.c -- procedures for maintaining the extended-key map
@item
map.c -- editor function definitions
@item
parse.c -- parse an editline extended command
@item
prompt.c -- prompt printing functions
@item
read.c -- terminal read functions
@item
readline.c -- read line
@item
refresh.c -- "lower level screen refreshing functions"
@item
search.c -- "history and character search functions"
@item
sig.c -- for signal handling
@item
strlcpy.c -- string copy
@item
term.c -- "editor/termcap-curses interface"
@item
tokenizer.c -- Bourne shell line tokenizer
@item
tty.c -- for a tty interface
@item
vi.c -- commands used when in the vi (editor) mode
@end itemize
@*@*
@subsection dbug
Fred Fish's dbug library.
@*@*
This is not really part of the MySQL package. Rather, it's a set of
public-domain routines which are useful for debugging MySQL programs.
@*@*
How it works: One inserts a function call that begins with DBUG_* in
one of the regular MYSQL programs. For example, in get_password.c, you
will find this line: @*
DBUG_ENTER("get_tty_password"); @*
at the start of a routine, and this line: @*
DBUG_RETURN(my_strdup(to,MYF(MY_FAE))); @*
at the end of the routine. These lines don't affect production code.
Features of the dbug library include profiling and state pushing.
@*@*
The C programs in this directory are:
@itemize @bullet
@item
dbug.c -- The main module
@item
dbug_analyze.c -- Reads a file produced by trace functions
@item
example1.c -- A tiny example
@item
example2.c -- A tiny example
@item
example3.c -- A tiny example
@item
factorial.c -- A tiny example
@item
main.c -- A tiny example
@item
sanity.c -- Declaration of a variable
@end itemize
@*@*
@subsection div
Deadlock test.
@*@*
This file contains only one program, deadlock_test.c.
@*@*
@subsection Docs
Preliminary documents about internals and new modules.
@*@*
This directory doesn't have much at present that's very useful to the
student, but the plan is that some documentation related to the source
files and the internal workings of MySQL, including perhaps some
documentation from developers themselves, will be placed here.
@*@*
These sub-directories are part of this directory:
@itemize @bullet
@item
books -- .gif images and empty .txt files; no real information
@item
flags -- images of flags of countries
@item
images -- flag backgrounds and the MySQL dolphin logo
@item
mysql-logos -- more MySQL-related logos, some of them moving
@item
raw-flags -- more country flags, all .gif files
@item
support -- various files for generating texinfo/docbook
documentation
@item
to-be-included... -- an empty subdirectory
@item
translations -- some Portuguese myodbc documentation
@end itemize
@*@*
In the main directory, you'll find some .txt files related to the
methods that MySQL uses to produce its printed and html documents, odd
bits in various languages, and the single file in the directory which
has any importance -- internals.texi -- The "MySQL Internals"
document.
@*@*
Despite the name, internals.texi is not really much of a description
of MySQL internals. However, there is some useful description of the
functions in the mysys directory (see below), and of the structure of
client/server messages (doubtless very useful for people who want to
make their own JDBC drivers, or just sniff).
@*@*
@subsection extra
Eight minor standalone utility programs.
@*@*
These eight programs are all standalone utilities, that is, they have
a main() function and their main role is to show information that the
MySQL server needs or produces. Most are unimportant. They are as
follows:
@itemize @bullet
@item
my_print_defaults.c -- print all parameters in a default file
@item
mysql_install.c -- startup: install MySQL server
@item
mysql_waitpid.c -- wait for a program to terminate
@item
perror.c -- "print error" -- given error number, display message
@item
replace.c -- replace strings in text files
@item
resolve_stack_dump.c -- show symbolic info from a stack dump
@item
resolveip.c -- convert an IP address to a hostname, or vice versa
@end itemize
@*@*
@subsection fs
File System.
@*@*
Here the word "File System" does not refer to the mere idea of a
directory of files on a disk drive, but to object-based access. The
concept has been compared with Oracle's Internet File System (iFS).
@*@*
The original developer of the files on this directory is Tonu Samuel,
a former MySQL AB employee. Here is a quote (somewhat edited) from
Tonu Samuel's web page (http://no.spam.ee/~tonu/index.php):
"Question: What is it?
Answer: Actually this is not filesystem in common terms. MySQL FS
makes it possible to make SQL tables and some functions available over
a filesystem. MySQL does not require disk space, it uses an ordinary
MySQL daemon to store data."
The descriptions imply that this is a development project.
@*@*
There are four program files in the directory:
@itemize @bullet
@item
database.c -- "emulate filesystem behaviour on top of SQL database"
@item
libmysqlfs.c -- Search/replace, show-functions, and parse routines
@item
mysqlcorbafs.c -- Connection with the CORBA "Object Request Broker"
@item
mysqlcorbafs_test.c -- Utility to test the working of mysqlcorbafs.c
@*@*
@subsection heap
The HEAP table handler.
@*@*
All the MySQL table handlers (i.e. the handlers that MySQL itself
produces) have files with similar names and functions. Thus, this
(heap) directory contains a lot of duplication of the myisam directory
(for the MyISAM table handler). Such duplicates have been marked with
an "*" in the following list. For example, you will find that
\heap\hp_extra.c has a close equivalent in the myisam directory
(\myisam\mi_extra.c) with the same descriptive comment.
@*@*
@item
hp_block.c -- Read/write a block (i.e. a page)
@item
hp_clear.c -- Remove all records in the database
@item
hp_close.c -- * close database
@item
hp_create.c -- * create a table
@item
hp_delete.c -- * delete a row
@item
hp_extra.c -- * for setting options and buffer sizes when optimizing
@item
hp_hash.c -- Hash functions used for saving keys
@item
hp_info.c -- * Information about database status
@item
hp_open.c -- * open database
@item
hp_panic.c -- * the hp_panic routine, probably for sudden shutdowns
@item
hp_rename.c -- * rename a table
@item
hp_rfirst.c -- * read first row through a specific key (very short)
@item
hp_rkey.c -- * read record using a key
@item
hp_rlast.c -- * read last row with same key as previously-read row
@item
hp_rnext.c -- * read next row with same key as previously-read row
@item
hp_rprev.c -- * read previous row with same key as previously-read
row
@item
hp_rrnd.c -- * read a row based on position
@item
hp_rsame.c -- * find current row using positional read or key-based
read
@item
hp_scan.c -- * read all rows sequentially
@item
hp_static.c -- * static variables (very short)
@item
hp_test1.c -- * testing basic functions
@item
hp_test2.c -- * testing database and storing results
@item
hp_update.c -- * update an existing row
@item
hp_write.c -- * insert a new row
@end itemize
@*@*
There are fewer files in the heap directory than in the myisam
directory, because fewer are necessary. For example, there is no need
for a \myisam\mi_cache.c equivalent (to cache reads) or a
\myisam\log.c equivalent (to log statements).
@*@*
@subsection Images
Empty directory.
@*@*
There are no files in this directory.
@*@*
@subsection include
Include (*.h) files.
@*@*
These files may be included in C program files. Note that each
individual directory will also have its own *.h files, for including
in its own *.c programs. The *.h files in the include directory are
ones that might be included from more than one place.
@*@*
For example, the mysys directory contains a C file named rijndael.c,
but does not include rijndael.h. The include directory contains
rijndael.h. Looking further, you'll find that rijndael.h is also
included in other places: by my_aes.c and my_aes.h.
@*@*
The include directory contains 51 *.h (include) files.
@*@*
@subsection innobase
The Innobase (InnoDB) table handler.
@*@*
A full description of these files can be found elsewhere in this
document.
@*@*
@subsection isam
The ISAM table handler.
@*@*
The C files in this directory are:
@itemize @bullet
@item
_cache.c -- for reading records from a cache
@item
changed.c -- a single routine for setting a "changed" flag (very
short)
@item
close.c -- close database
@item
create.c -- create a table
@item
_dbug.c -- support routines for use with "dbug" (see the \dbug
description)
@item
delete.c -- delete a row
@item
_dynrec.c -- functions to handle space-packed records and blobs
@item
extra.c -- setting options and buffer sizes when optimizing table
handling
@item
info.c -- Information about database status
@item
_key.c -- for handling keys
@item
_locking.c -- lock database
@item
log.c -- save commands in log file which myisamlog program can read
@item
_packrec.c -- compress records
@item
_page.c -- read and write pages containing keys
@item
panic.c -- the mi_panic routine, probably for sudden shutdowns
@item
range.c -- approximate count of how many records lie between two
keys
@item
rfirst.c -- read first row through a specific key (very short)
@item
rkey.c -- read a record using a key
@item
rlast.c -- read last row with same key as previously-read row
@item
rnext.c -- read next row with same key as previously-read row
@item
rprev.c -- read previous row with same key as previously-read row
@item
rrnd.c -- read a row based on position
@item
rsame.c -- find current row using positional read or key-based read
@item
rsamepos.c -- positional read
@item
_search.c -- key-handling functions
@item
static.c -- static variables (very short)
@item
_statrec.c -- functions to handle fixed-length records
@item
test1.c -- testing basic functions
@item
test2.c -- testing database and storing results
@item
test3.c -- testing locking
@item
update.c -- update an existing row
@item
write.c -- insert a new row
@item
pack_isam.c -- pack isam file (NOTE TO SELF ?? equivalent to
\myisam\myisampack.c)
@end itemize
@*@*
Except for one minor C file (pack_isam.c) every program in the ISAM
directory has a counterpart in the MyISAM directory. For example
\isam\update.c corresponds to \myisam\mi_update.c. However, the
reverse is not true -- there are many files in the MyISAM directory
which have no counterpart in the ISAM directory.
@*@*
The reason is simple -- it's because the ISAM files are becoming
obsolete. When MySQL programmers add new features, they add them for
MyISAM only. The student can therefore ignore all files in this
directory and study the MyISAM programs instead.
@*@*
@subsection libmysql
The MySQL Library, Part 1.
@*@*
The files here are for producing MySQL as a library (e.g. a Windows
DLL). The idea is that, instead of producing separate mysql (client)
and mysqld (server) programs, one produces a library. Instead of
sending messages, the client part merely calls the server part.
@*@*
The libmysql files are split into three directories: libmysql (this
one), libmysql_r (the next one), and libmysqld (the next one after
that). It may be that the original intention was that the libmysql
directory would hold the "client part" files, and the libmysqld
directory would hold the "server part" files.
@*@*
The program files on this directory are:
@itemize @bullet
@item
conf_to_src.c -- has to do with charsets
@item
dll.c -- initialization of the dll library
@item
errmsg.c -- English error messages, compare \mysys\errors.c
@item
get_password.c -- get password
@item
libmysql.c -- the main "packet-sending emulation" program
@item
manager.c -- initialize/connect/fetch with MySQL manager
@end itemize
@*@*
@subsection libmysql_r
The MySQL Library, Part 2.
@*@*
This is a continuation of the libmysql directory. There is only one
file here:
@itemize @bullet
@item
makefile.am
@end itemize
@*@*
@subsection libmysqld
The MySQL library, Part 3.
@*@*
This is a continuation of the libmysql directory. The program files on
this directory are:
@itemize @bullet
@item
libmysqld.c -- The called side, compare the mysqld.exe source
@item
lib_vio.c -- Emulate the vio directory's communication buffer
@end itemize
@*@*
@subsection man
Manual pages.
@*@*
These are not the actual "man" (manual) pages, they are switches for
the production.
@*@*
@subsection merge
The MERGE table handler.
@*@*
For a description of the MERGE table handler, see the MySQL Reference
Manual, section 7.2.
@*@*
You'll notice that there seem to be several directories with
similar-sounding names of C files in them. That's because the MySQL
table handlers are all quite similar.
@*@*
The related directories are:
@itemize @bullet
@item
\isam -- for ISAM
@item
\myisam -- for MyISAM
@item
\merge -- for ISAM MERGE (mostly call functions in \isam programs)
@item
\myisammrg -- for MyISAM MERGE (mostly call functions in \myisam
programs)
@end itemize
@*@*
To avoid duplication, only the \myisam program versions are discussed.
@*@*
The C programs in this (merge) directory are:
@itemize @bullet
@item
mrg_close.c -- compare \isam's close.c
@item
mrg_create.c -- "" create.c
@item
mrg_delete.c -- "" delete.c
@item
mrg_extra.c -- "" extra.c
@item
mrg_info.c -- "" info.c
@item
mrg_locking.c -- "" locking.c
@item
mrg_open.c -- "" open.c
@item
mrg_panic.c -- "" panic.c
@item
mrg_rrnd.c -- "" rrnd.c
@item
mrg_rsame.c -- "" rsame.c
@item
mrg_static.c -- "" static.c
@item
mrg_update.c -- "" update.c
@end itemize
@*@*
@subsection myisam
The MyISAM table handler.
@*@*
The C files in this subdirectory come in six main groups:
@itemize @bullet
@item
ft*.c files -- ft stands for "Full Text", code contributed by Sergei
Golubchik
@item
mi*.c files -- mi stands for "My Isam", these are the main programs
for Myisam
@item
myisam*.c files -- for example, "myisamchk" utility routine
functions source
@item
rt*.c files -- rt stands for "rtree", some code was written by
Alexander Barkov
@item
sp*.c files -- sp stands for "spatial", some code was written by
Ramil Kalimullin
@item
sort.c -- this is a single file that sorts keys for index-create
purposes
@end itemize
@*@*
The "full text" and "rtree" and "spatial" program sets are for special
purposes, so this document focuses only on the mi*.c "myisam" C
programs. They are:
@itemize @bullet
@item
mi_cache.c -- for reading records from a cache
@item
mi_changed.c -- a single routine for setting a "changed" flag (very
short)
@item
mi_check.c -- doesn't just do checks, ?? for myisamchk program?
@item
mi_checksum.c -- calculates a checksum for a row
@item
mi_close.c -- close database
@item
mi_create.c -- create a table
@item
mi_dbug.c -- support routines for use with "dbug" (see \dbug
description)
@item
mi_delete.c -- delete a row
@item
mi_delete_all.c -- delete all rows
@item
mi_delete_table.c -- delete a table (very short)
@item
mi_dynrec.c -- functions to handle space-packed records and blobs
@item
mi_extra.c -- setting options and buffer sizes when optimizing
@item
mi_info.c -- "Ger tillbaka en struct med information om isam-filen"
@item
mi_key.c -- for handling keys
@item
mi_locking.c -- lock database
@item
mi_log.c -- save commands in log file which myisamlog program can
read
@item
mi_open.c -- open database
@item
mi_packrec.c -- compress records
@item
mi_page.c -- read and write pages containing keys
@item
mi_panic.c -- the mi_panic routine, probably for sudden shutdowns
@item
mi_range.c -- approximate count of how many records lie between two
keys
@item
mi_rename.c -- rename a table
@item
mi_rfirst.c -- read first row through a specific key (very short)
@item
mi_rkey.c -- read a record using a key
@item
mi_rlast.c -- read last row with same key as previously-read row
@item
mi_rnext.c -- read next row with same key as previously-read row
@item
mi_rnext_same.c -- same as mi_rnext.c, but abort if the key changes
@item
mi_rprev.c -- read previous row with same key as previously-read row
@item
mi_rrnd.c -- read a row based on position
@item
mi_rsame.c -- find current row using positional read or key-based
read
@item
mi_rsamepos.c -- positional read
@item
mi_scan.c -- read all rows sequentially
@item
mi_search.c -- key-handling functions
@item
mi_static.c -- static variables (very short)
@item
mi_statrec.c -- functions to handle fixed-length records
@item
mi_test1.c -- testing basic functions
@item
mi_test2.c -- testing database and storing results
@item
mi_test3.c -- testing locking
@item
mi_unique.c -- functions to check if a row is unique
@item
mi_update.c -- update an existing row
@item
mi_write.c -- insert a new row
@end itemize
@*@*
@subsection myisammrg
MyISAM Merge table handler.
@*@*
As with other table handlers, you'll find that the *.c files in the
myissammrg directory have counterparts in the myisam directory. In
fact, this general description of a myisammrg program is almost always
true: The myisammrg
function checks an argument, the myisammrg function formulates an
expression for passing to a myisam function, the myisammrg calls a
myisam function, the myisammrg function returns.
@*@*
These are the 21 files in the myisammrg directory, with notes about
the myisam functions or programs they're connected with:
@itemize @bullet
@item
myrg_close.c -- mi_close.c
@item
myrg_create.c -- mi_create.c
@item
myrg_delete.c -- mi_delete.c / delete last-read record
@item
myrg_extra.c -- mi_extra.c / "extra functions we want to do ..."
@item
myrg_info.c -- mi_info.c / display information about a mymerge file
@item
myrg_locking.c -- mi_locking.c / lock databases
@item
myrg_open.c -- mi_open.c / open a MyISAM MERGE table
@item
myrg_panic.c -- mi_panic.c / close in a hurry
@item
myrg_queue.c -- read record based on a key
@item
myrg_range.c -- mi_range.c / find records in a range
@item
myrg_rfirst.c -- mi_rfirst.c / read first record according to
specific key
@item
myrg_rkey.c -- mi_rkey.c / read record based on a key
@item
myrg_rlast.c -- mi_rlast.c / read last row with same key as previous
read
@item
myrg_rnext.c -- mi_rnext.c / read next row with same key as previous
read
@item
myrg_rnext_same.c -- mi_rnext_same.c / read next row with same key
@item
myrg_rprev.c -- mi_rprev.c / read previous row with same key
@item
myrg_rrnd.c -- mi_rrnd.c / read record with random access
@item
myrg_rsame.c -- mi_rsame.c / call mi_rsame function, see
\myisam\mi_rsame.c
@item
myrg_static.c -- mi_static.c / static variable declaration
@item
myrg_update.c -- mi_update.c / call mi_update function, see
\myisam\mi_update.c
@item
myrg_write.c -- mi_write.c / call mi_write function, see
\myisam\mi_write.c
@end itemize
@*@*
@subsection mysql-test
A test suite for mysqld.
@*@*
The directory has a README file which explains how to run the tests,
how to make new tests (in files with the filename extension "*.test"),
and how to report errors.
@*@*
There are four subdirectories:
@itemize @bullet
@item
\misc -- contains one minor Perl program
@item
\r -- contains *.result, i.e. "what happened" files and
*.required, i.e. "what should happen" file
@item
\std_data -- contains standard data for input to tests
@item
\t -- contains tests
@end itemize
@*@*
There are 186 *.test files in the \t subdirectory. Primarily these are
SQL scripts which try out a feature, output a result, and compare the
result with what's required. Some samples of what the test files check
are: latin1_de comparisons, date additions, the HAVING clause, outer
joins, openSSL, load data, logging, truncate, and UNION.
@*@*
There are other tests in these directories:
@itemize @bullet
@item
sql-bench
@item
repl-tests
@item
tests
@end itemize
@subsection mysys
MySQL system library (Low level routines for file access etc.).
@*@*
There are 115 *.c programs in this directory:
@itemize @bullet
@item
array.c -- Dynamic array handling
@item
charset.c -- Using dynamic character sets, set default character
set, ...
@item
charset2html.c -- Checking what character set a browser is using
@item
checksum.c -- Calculate checksum for a memory block, used for
pack_isam
@item
default.c -- Find defaults from *.cnf or *.ini files
@item
errors.c -- English text of global errors
@item
hash.c -- Hash search/compare/free functions "for saving keys"
@item
list.c -- Double-linked lists
@item
make-conf.c -- "Make a charset .conf file out of a ctype-charset.c
file"
@item
md5.c -- MD5 ("Message Digest 5") algorithm from RSA Data Security
@item
mf_brkhant.c -- Prevent user from doing a Break during critical
execution
@item
mf_cache.c -- "Open a temporary file and cache it with io_cache"
@item
mf_dirname.c -- Parse/convert directory names
@item
mf_fn_ext.c -- Get filename extension
@item
mf_format.c -- Format a filename
@item
mf_getdate.c -- Get date, return in yyyy-mm-dd hh:mm:ss format
@item
mf_iocache.c -- Cached read/write of files in fixed-size units
@item
mf_iocache2.c -- Continuation of mf_iocache.c
@item
mf_keycache.c -- Key block caching for certain file types
@item
mf_loadpath.c -- Return full path name (no ..\ stuff)
@item
mf_pack.c -- Packing/unpacking directory names for create purposes
@item
mf_path.c -- Determine where a program can find its files
@item
mf_qsort.c -- Quicksort
@item
mf_qsort2.c -- Quicksort, part 2
@item
mf_radix.c -- Radix sort
@item
mf_same.c -- Determine whether filenames are the same
@item
mf_sort.c -- Sort with choice of Quicksort or Radix sort
@item
mf_soundex.c -- Soundex algorithm derived from EDN Nov. 14, 1985
(pg. 36)
@item
mf_strip.c -- Strip trail spaces from a string
@item
mf_tempdir.c -- Initialize/find/free temporary directory
@item
mf_tempfile.c -- Create a temporary file
@item
mf_unixpath.c -- Convert filename to UNIX-style filename
@item
mf_util.c -- Routines, #ifdef'd, which may be missing on some
machines
@item
mf_wcomp.c -- Comparisons with wildcards
@item
mf_wfile.c -- Finding files with wildcards
@item
mulalloc.c -- Malloc many pointers at the same time
@item
my_aes.c -- AES encryption
@item
my_alarm.c -- Set a variable value when an alarm is received
@item
my_alloc.c -- malloc of results which will be freed simultaneously
@item
my_append.c -- one file to another
@item
my_bit.c -- smallest X where 2^X >= value, maybe useful for
divisions
@item
my_bitmap.c -- Handle uchar arrays as large bitmaps
@item
my_chsize.c -- Truncate file if shorter, else fill with a filler
character
@item
my_clock.c -- Time-of-day ("clock()") function, with OS-dependent
#ifdef's
@item
my_compress.c -- Compress packet (see also description of \zlib
directory)
@item
my_copy.c -- Copy files
@item
my_create.c -- Create file
@item
my_delete.c -- Delete file
@item
my_div.c -- Get file's name
@item
my_dup.c -- Open a duplicated file
@item
my_error.c -- Return formatted error to user
@item
my_fopen.c -- File open
@item
my_fstream.c -- Streaming file read/write
@item
my_getwd.c -- Get working directory
@item
my_gethostbyname.c -- Thread-safe version of standard net
gethostbyname() func
@item
my_getopt.c -- Find out what options are in effect
@item
my_handler.c -- Compare two keys in various possible formats
@item
my_init.c -- Initialize variables and functions in the mysys library
@item
my_lib.c -- Compare/convert directory names and file names
@item
my_lock.c -- Lock part of a file
@item
my_lockmem.c -- "Allocate a block of locked memory"
@item
my_lread.c -- Read a specified number of bytes from a file into
memory
@item
my_lwrite.c -- Write a specified number of bytes from memory into a
file
@item
my_malloc.c -- Malloc (memory allocate) and dup functions
@item
my_messnc.c -- Put out a message on stderr with "no curses"
@item
my_mkdir.c -- Make directory
@item
my_net.c -- Thread-safe version of net inet_ntoa function
@item
my_netware.c -- Functions used only with the Novell Netware version
of MySQL
@item
my_once.c -- Allocation / duplication for "things we don't need to
free"
@item
my_open.c -- Open a file
@item
my_os2cond.c -- OS2-specific: "A simple implementation of posix
conditions"
@item
my_os2dirsrch.c -- OS2-specific: Emulate a Win32 directory search
@item
my_os2dlfcn.c -- OS2-specific: Emulate UNIX dynamic loading
@item
my_os2file64.c -- OS2-specific: For File64bit setting
@item
my_os2mutex.c -- OS2-specific: For mutex handling
@item
my_os2thread.c -- OS2-specific: For thread handling
@item
my_os2tls.c -- OS2-specific: For thread-local storage
@item
my_port.c -- AIX-specific: my_ulonglong2double()
@item
my_pread.c -- Read a specified number of bytes from a file
@item
my_pthread.c -- A wrapper for thread-handling functions in different
OSs
@item
my_quick.c -- Read/write (labelled a "quicker" interface, perhaps
obsolete)
@item
my_read.c -- Read a specified number of bytes from a file, possibly
retry
@item
my_realloc.c -- Reallocate memory allocated with my_alloc.c
(probably)
@item
my_redel.c -- Rename and delete file
@item
my_rename.c -- Rename without delete
@item
my_seek.c -- Seek, i.e. point to a spot within a file
@item
my_semaphore.c -- Semaphore routines, for use on OS that doesn't
support them
@item
my_sleep.c -- Wait n microseconds
@item
my_static.c -- Static-variable definitions
@item
my_symlink.c -- Read a symbolic link (symlinks are a UNIX thing, I
guess)
@item
my_symlink2.c -- Part 2 of my_symlink.c
@item
my_tempnam.c -- Obsolete temporary-filename routine used by ISAM
table handler
@item
my_thr_init.c -- initialize/allocate "all mysys & debug thread
variables"
@item
my_wincond.c -- Windows-specific: emulate Posix conditions
@item
my_winsem.c -- Windows-specific: emulate Posix threads
@item
my_winthread.c -- Windows-specific: emulate Posix threads
@item
my_write.c -- Write a specified number of bytes to a file
@item
ptr_cmp.c -- Point to an optimal byte-comparison function
@item
queues.c -- Handle priority queues as in Robert Sedgewick's book
@item
raid2.c -- RAID support (the true implementation is in raid.cc)
@item
rijndael.c -- "Optimised ANSI C code for the Rijndael cipher (now
AES")
@item
safemalloc.c -- A version of the standard malloc() with safety
checking
@item
sha1.c -- Implementation of Secure Hashing Algorithm 1
@item
string.c -- Initialize/append/free dynamically-sized strings
@item
testhash.c -- Standalone program: test the hash library routines
@item
test_charset.c -- Standalone program: display character set
information
@item
test_dir.c -- Standalone program: placeholder for "test all
functions" idea
@item
test_fn.c -- Standalone program: apparently tests a function
@item
test_xml.c -- Standalone program: test XML routines
@item
thr_alarm.c -- Thread alarms and signal handling
@item
thr_lock.c -- "Read and write locks for Posix threads"
@item
thr_mutex.c -- A wrapper for mutex functions
@item
thr_rwlock.c -- Synchronizes the readers' thread locks with the
writer's lock
@item
tree.c -- Initialize/search/free binary trees
@item
typelib.c -- Determine what type a field has
@end itemize
@*@*
You can find documentation for the main functions in these files
elsewhere in this document.
For example, the main functions in my_getwd.c are described thus:
@*@*
@example
"int my_getwd _A((string buf, uint size, myf MyFlags)); @*
int my_setwd _A((const char *dir, myf MyFlags)); @*
Get and set working directory." @*
@end example
@subsection netware
Files related to the Novell NetWare version of MySQL.
@*@*
There are 39 files on this directory. Most have filename extensions of
*.def, *.sql, or *.c.
@*@*
The twenty-five *.def files are all from Novell Inc. They contain import or
export symbols. (".def" is a common filename extension for
"definition".)
@*@*
The two *.sql files are short scripts of SQL statements used in
testing.
@*@*
These are the five *.c files, all from Novell Inc.:
@itemize @bullet
@item
libmysqlmain.c -- Only one function: init_available_charsets()
@item
my_manage.c -- Standalone management utility
@item
mysql_install_db.c -- Compare \scripts\mysql_install_db.sh
@item
mysql_test_run.c -- Short test program
@item
mysqld_safe.c -- Compare \scripts\mysqld_safe.sh
@end itemize
Perhaps the most important file is:
@itemize @bullet
@item
netware.patch -- NetWare-specific build instructions and switches
(compare \mysql-4.1\ltmain.sh)
@end itemize
@*@*
For instructions about basic installation, see "Deployment Guide For
NetWare AMP" at:
@url{http://developer.novell.com/ndk/whitepapers/namp.htm}
@*
@subsection NEW-RPMS
New "RPM Package Manager" files.
@*@*
This directory is not part of the Windows distribution. Perhaps in
MYSQL's Linux distribution it has files for use with Red Hat
installations -- a point that needs checking someday.
@*@*
@subsection os2
Routines for working with the OS2 operating system.
@*@*
The files in this directory are the product of the efforts of three
people from outside MySQL: Yuri Dario, Timo Maier, and John M
Alfredsson. There are no .C program files in this directory.
@*@*
The contents of \os2 are:
@itemize @bullet
@item
A Readme.Txt file
@item
An \include subdirectory containing .h files which are for OS/2 only
@item
Files used in the build process (configuration, switches, and one
.obj)
@end itemize
@*@*
The README file refers to MySQL version 3.23, which suggests that
there have been no updates for MySQL 4.0 for this section.
@*@*
@subsection pstack
Process stack display.
@*@*
This is a set of publicly-available debugging aids which all do pretty
well the same thing: display the contents of the stack, along with
symbolic information, for a running process. There are versions for
various object file formats (such as ELF and IEEE-695). Most of the
programs are copyrighted by the Free Software Foundation and are
marked as "part of GNU Binutils".
@*@*
In other words, the pstack files are not really part of the MySQL
library. They are merely useful when you re-program some MYSQL code
and it crashes.
@*@*
@subsection regex
Regular Expression library for support of REGEXP function.
@*@*
This is the copyrighted product of Henry Spencer from the University
of Toronto. It's a fairly-well-known implementation of the
requirements of POSIX 1003.2 Section 2.8. The library is bundled with
Apache and is the default implementation for regular-expression
handling in BSD Unix. MySQL's Monty Widenius has made minor changes in
three programs (debug.c, engine.c, regexec.c) but this is not a MySQL
package. MySQL calls it only in order to support two MySQL functions:
REGEXP and RLIKE.
@*@*
Some of Mr Spencer's documentation for the regex library can be found
in the README and WHATSNEW files.
@*@*
One MySQL program which uses regex is \cmd-line-utils\libedit\search.c
@*@*
This program calls the 'regcomp' function, which is the entry point in
\regex\regexp.c.
@*@*
@subsection repl-tests
Test cases for replication.
@*@*
There are six short and trivial-looking tests in these subdirectories:
@itemize @bullet
@item
\test-auto-inc -- Do auto-Increment columns work?
@item
\test-bad-query -- Does insert in PK column work?
@item
\test-dump -- Do LOAD statements work?
@item
\test-repl -- Does replication work?
@item
\test-repl-alter -- Does ALTER TABLE work?
@item
\test-repl-ts -- Does TIMESTAMP column work?
@end itemize
@*@*
@subsection SCCS
Source Code Control System.
@*@*
You will see this directory if and only if you used BitKeeper for
downloading the source. The files here are for BitKeeper
administration and are not of interest to application programmers.
@*@*
@subsection scripts
SQL batches, e.g. for converting msql to MySQL.
@*@*
The *.sh filename extension apparently stands for "shell script".
Linux programmers use it where Windows programmers would use a *.bat
(batch filename extension).
@*@*
The *.sh files on this directory are:
@itemize @bullet
@item
fill_help_tables.sh -- Create help-information tables and insert
@item
make_binary_distribution.sh -- Get configure information, make,
produce tar
@item
msql2mysql.sh -- Convert mSQL to MySQL
@item
mysqlbug.sh -- Create a bug report and mail it
@item
mysqld_multi.sh -- Start/stop any number of mysqld instances
@item
mysqld_safe-watch.sh -- Start/restart in safe mode
@item
mysqld_safe.sh -- Start/restart in safe mode
@item
mysqldumpslow.sh -- Parse and summarize the slow query log
@item
mysqlhotcopy.sh -- Hot backup
@item
mysql_config.sh -- Get configure information that client might need
@item
mysql_convert_table_format.sh -- Conversion, e.g. from ISAM to
MyISAM
@item
mysql_explain_log.sh -- Put a log (made with --log) into a MySQL
table
@item
mysql_find_rows.sh -- Search for queries containing <regexp>
@item
mysql_fix_extensions.sh -- Renames some file extensions, not
recommended
@item
mysql_fix_privilege_tables.sh -- Fix mysql.user etc. if upgrading to
MySQL 3.23.14+
@item
mysql_install_db.sh -- Create privilege tables and func table
@item
mysql_secure_installation.sh -- Disallow remote root login,
eliminate test, etc.
@item
mysql_setpermission.sh -- Aid to add users or databases, sets
privileges
@item
mysql_tableinfo.sh -- Puts info re MySQL tables into a MySQL table
@item
mysql_zap.sh -- Kill processes which match pattern
@end itemize
@*@*
@subsection sql
Programs for handling SQL commands. The "core" of MySQL.
@*@*
These are the .c and .cc files in the sql directory:
@itemize @bullet
@item
cache_manager.cc -- manages a number of blocks
@item
convert.cc -- convert tables between different character sets
@item
derror.cc -- read language-dependent message file
@item
des_key_file.cc -- load DES keys from plaintext file
@item
field.cc -- "implement classes defined in field.h" (long)
@item
field_conv.cc -- functions to copy data to or from fields
@item
filesort.cc -- sort file
@item
frm_crypt.cc -- contains only one short function: get_crypt_for_frm
@item
gen_lex_hash.cc -- Knuth's algorithm from Vol 3 Sorting and
Searching, Chapter 6.3
@item
gstream.cc -- GTextReadStream
@item
handler.cc -- handler-calling functions
@item
hash_filo.cc -- static-sized hash tables
@item
ha_berkeley.cc -- Handler: BDB
@item
ha_heap.cc -- Handler: Heap
@item
ha_innodb.cc -- Handler: InnoDB
@item
ha_isam.cc -- Handler: ISAM
@item
ha_isammrg.cc -- Handler: (ISAM MERGE)
@item
ha_myisam.cc -- Handler: MyISAM
@item
ha_myisammrg.cc -- Handler: (MyISAM MERGE)
@item
hostname.cc -- Given IP, return hostname
@item
init.cc -- Init and dummy functions for interface with unireg
@item
item.cc -- Item functions
@item
item_buff.cc -- Buffers to save and compare item values
@item
item_cmpfunc.cc -- Definition of all compare functions
@item
item_create.cc -- Create an item. Used by lex.h.
@item
item_func.cc -- Numerical functions
@item
item_row.cc -- Row items for comparing rows and for IN on rows
@item
item_sum.cc -- Set functions (sum, avg, etc.)
@item
item_strfunc.cc -- String functions
@item
item_subselect.cc -- Item subselect
@item
item_timefunc.cc -- Date/time functions, e.g. week of year
@item
item_uniq.cc -- Empty file, here for compatibility reasons
@item
key.cc -- Functions to handle keys and fields in forms
@item
lock.cc -- Locks
@item
log.cc -- Logs
@item
log_event.cc -- Log event
@item
matherr.c -- Handling overflow, underflow, etc.
@item
mf_iocache.cc -- Caching of (sequential) reads
@item
mini_client.cc -- Client included in server for server-server
messaging
@item
mysqld.cc -- Source of mysqld.exe
@item
my_lock.c -- Lock part of a file
@item
net_serv.cc -- Read/write of packets on a network socket
@item
nt_servc.cc -- Initialize/register/remove an NT service
@item
opt_ft.cc -- Create a FT or QUICK RANGE based on a key (very short)
* opt_range.cc -- Range of keys
@item
opt_sum.cc -- Optimize functions in presence of (implied) GROUP BY
@item
password.c -- Password checking
@item
procedure.cc -- Procedure
@item
protocol.cc -- Low level functions for storing data to be sent to
client
@item
records.cc -- Functions to read, write, and lock records
@item
repl_failsafe.cc -- Replication fail-save
@item
set_var.cc -- MySQL variables
@item
slave.cc -- Procedures for a slave in a master/slave (replication?)
relation
@item
spatial.cc -- Geometry stuff (lines, points, etc.)
@item
sql_acl.cc -- Functions related to ACL security
@item
sql_analyse.cc -- Analyse an input string (?)
@item
sql_base.cc -- Basic functions needed by many modules
@item
sql_cache.cc -- SQL cache, with long comments about how caching
works
@item
sql_class.cc -- SQL class
@item
sql_crypt.cc -- Encode / decode, very short
@item
sql_db.cc -- Create / drop database
@item
sql_delete.cc -- The DELETE statement
@item
sql_derived.cc -- Derived tables, with long comments
@item
sql_do.cc -- The DO statement
@item
sql_error.cc -- Errors and warnings
@item
sql_handler.cc -- Direct access to ISAM
@item
sql_help.cc -- The HELP statement (if there is one?)
@item
sql_insert.cc -- The INSERT statement
@item
sql_lex.cc -- Related to lex or yacc
@item
sql_list.cc -- Only list_node_end_of_list, short
@item
sql_load.cc -- The LOAD DATA statement?
@item
sql_map.cc -- Memory-mapped files?
@item
sql_manager.cc -- Maintenance tasks, e.g. flushing the buffers
periodically
@item
sql_olap.cc -- ROLLUP
@item
sql_parse.cc -- Parse an SQL statement
@item
sql_prepare.cc -- Prepare an SQL statement
@item
sql_repl.cc -- Replication
@item
sql_rename.cc -- Rename table
@item
sql_select.cc -- Select and join optimisation
@item
sql_show.cc -- The SHOW statement
@item
sql_string.cc -- String functions: alloc, realloc, copy, convert,
etc.
@item
sql_table.cc -- The DROP TABLE and ALTER TABLE statements
@item
sql_test.cc -- Some debugging information
@item
sql_udf.cc -- User-defined functions
@item
sql_union.cc -- The UNION operator
@item
sql_update.cc -- The UPDATE statement
@item
stacktrace.c -- Display stack trace (Linux/Intel only?)
@item
table.cc -- Table metadata retrieval, mostly
@item
thr_malloc.cc -- Mallocs used in threads
@item
time.cc -- Date and time functions
@item
udf_example.cc -- Example file of user-defined functions
@item
uniques.cc -- Function to handle quick removal of duplicates
@item
unireg.cc -- Create a unireg form file from a FIELD and field-info struct
@end itemize
@*@*
@subsection sql-bench
The MySQL Benchmarks.
@*@*
This directory has the programs and input files which MySQL uses for
its comparisons of MySQL, PostgreSQL, mSQL, Solid, etc. Since MySQL
publishes the comparative results, it's only right that it should make
available all the material necessary to reproduce all the tests.
@*@*
There are five subdirectories and sub-subdirectories:
@itemize @bullet
@item
\Comments -- Comments about results from tests of Access, Adabas,
etc.
@item
\Data\ATIS -- .txt files containing input data for the "ATIS" tests
@item
\Data\Wisconsin -- .txt files containing input data for the
"Wisconsin" tests
@item
\Results -- old test results
@item
\Results-win32 -- old test results from Windows 32-bit tests
@end itemize
@*@*
There are twenty-four *.sh (shell script) files, which involve Perl
programs.
@*@*
There are three *.bat (batch) files.
@*@*
There is one README file and one TODO file.
@*@*
@subsection SSL
Secure Sockets Layer.
@*@*
This isn't a code directory. It contains a short note from Tonu Samuel
(the NOTES file) and seven *.pem files. PEM stands for "Privacy
Enhanced Mail" and is an Internet standard for adding security to
electronic mail. Finally, there are two short scripts for running
clients and servers over SSL connections.
@*@*
@subsection strings
The string library.
@*@*
Many of the files in this subdirectory are equivalent to well-known
functions that appear in most C string libraries. For those, there is
documentation available in most compiler handbooks.
@*@*
On the other hand, some of the files are MySQL additions or
improvements. Often the MySQL changes are attempts to optimize the
standard libraries. It doesn't seem that anyone tried to optimize for
recent Pentium class processors, though.
@*@*
The .C files are:
@itemize @bullet
@item
atof.c -- ascii-to-float, MySQL version
@item
bchange.c -- short replacement routine written by Monty Widenius in
1987
@item
bcmp.c -- binary compare, rarely used
@item
bcopy-duff.c -- block copy: attempt to copy memory blocks faster
than cmemcpy
@item
bfill.c -- byte fill, to fill a buffer with (length) copies of a
byte
@item
bmove.c -- block move
@item
bmove512.c -- "should be the fastest way to move a multiple of 512
bytes"
@item
bmove_upp.c -- bmove.c variant, starting with last byte
@item
bzero.c -- something like bfill with an argument of 0
@item
conf_to_src.c -- reading a configuration file (NOTE TO SELF ? what's
this doing here?)
@item
ctype*.c -- string handling programs for each char type MySQL
handles
@item
do_ctype.c -- display case-conversion and sort-conversion tables
@item
int2str.c -- integer-to-string
@item
is_prefix.c -- checks whether string1 starts with string2
@item
llstr.c -- convert long long to temporary-buffer string, return
pointer
@item
longlong2str.c -- ditto, but to argument-buffer
@item
memcmp.c -- memory compare
@item
memset.c -- memory set
@item
my_vsnprintf.c -- variant of printf
@item
r_strinstr.c -- see if one string is within another
@item
str2int.c -- convert string to integer
@item
strappend.c -- append one string to another
@item
strcat.c -- concatenate strings
@item
strcend.c -- point to where a character C occurs within str, or NULL
@item
strchr.c -- point to first place in string where character occurs
@item
strcmp.c -- compare two strings
@item
strcont.c -- point to where any one of a set of characters appears
@item
strend.c -- point to the '\0' byte which terminates str
@item
strfill.c -- fill a string with n copies of a byte
@item
strinstr.c -- find string within string
@item
strlen.c -- return length of string in bytes
@item
strmake.c -- move n characters, or move till end
@item
strmov.c -- move source to dest and return pointer to end
@item
strnlen.c -- return length of string, or return n
@item
strnmov.c -- move source to dest for source size, or for n bytes
@item
strrchr.c -- find a character within string, searching from end
@item
strstr.c -- find an instance of pattern within source
@item
strto.c -- string to long, to long long, to unsigned long, etc.
@item
strtol.c -- string to long
@item
strtoll.c -- string to long long
@item
strtoul.c -- string to unsigned long
@item
strtoull.c -- string to unsigned long long
@item
strxmov.c -- move a series of concatenated source strings to dest
@item
strxnmov.c -- like strxmov.c but with a maximum length n
@item
str_test.c -- test of all the string functions encoded in assembler
@item
udiv.c -- unsigned long divide
@item
xml.c -- read and parse XML strings
@end itemize
@*@*
There are also four .ASM files -- macros.asm, ptr_cmp.asm,
strings.asm, and strxmov.asm -- which can replace some of the
C-program functions. But again, they look like optimizations for old
members of the Intel processor family.
@*@*
@subsection support-files
Support files.
@*@*
The files here are for building ("making") MySQL given a package
manager, compiler, linker, and other build tools. The support files
provide instructions and switches for the build processes.
@*@*
@subsection tests
Tests in Perl.
@*@*
These are tests that were run once to check for bugs in various
scenarios: forks, locks, big records, exporting, truncating, etc.
@*@*
@subsection tools
Tools -- well, actually, one tool.
@*@*
The only file is:
@itemize @bullet
@item
mysqlmanager.c -- A "server management daemon" by Sasha Pachev
@end itemize
@*@*
@subsection VC++Files
Visual C++ Files.
@*@*
Includes this entire directory, repeated for VC++ (Windows) use.
@*@*
VC++Files has subdirectories which are copies of the main directories.
For example there is a subdirectory \VC++Files\heap, which has the
same files as \heap. So for a description of the files in
\VC++Files\heap, see the description of the files in \heap. The same
applies for almost all of VC++Files's subdirectories (bdb, client,
isam, libmysql, etc.). The difference is that the \VC++Files variants
are specifically for compilation with Microsoft Visual C++ in 32-bit
Windows environments.
@*@*
In addition to the "subdirectories which are duplicates of
directories", VC++Files contains these subdirectories, which are not
duplicates:
@itemize @bullet
@item
comp_err -- (nearly empty)
@item
contrib -- (nearly empty)
@item
InstallShield script files
@item
isamchk -- (nearly empty)
@item
libmysqltest -- one small non-MySQL test program: mytest.c
@item
myisamchk -- (nearly empty)
@item
myisamlog -- (nearly empty)
@item
myisammrg -- (nearly empty)
@item
mysqlbinlog -- (nearly empty)
@item
mysqlmanager -- MFC foundation class files created by AppWizard
@item
mysqlserver -- (nearly empty)
@item
mysqlshutdown -- one short program, mysqlshutdown.c
@item
mysqlwatch.c -- Windows service initialization and monitoring
@item
my_print_defaults -- (nearly empty)
@item
pack_isam -- (nearly empty)
@item
perror -- (nearly empty)
@item
prepare -- (nearly empty)
@item
replace -- (nearly empty)
@item
SCCS -- source code control system
@item
test1 -- tests connecting via X threads
@item
thr_insert_test -- (nearly empty)
@item
thr_test -- one short program used to test for memory-allocation bug
@item
winmysqladmin -- the winmysqladmin.exe source. machine-generated?
@end itemize
@*@*
@subsection vio
Virtual I/O Library.
@*@*
The VIO routines are wrappers for the various network I/O calls that
happen with different protocols. The idea is that in the main modules
one won't have to write separate bits of code for each protocol. Thus
vio's purpose is somewhat like the purpose of Microsoft's winsock
library.
@*@*
The underlying protocols at this moment are: TCP/IP, Named Pipes (for
WindowsNT), Shared Memory, and Secure Sockets (SSL).
@*@*
The C programs are:
@itemize @bullet
@item
test-ssl.c -- Short standalone test program: SSL
@item
test-sslclient.c -- Short standalone test program: clients
@item
test-sslserver.c -- Short standalone test program: server
@item
vio.c -- Declarations + open/close functions
@item
viosocket.c -- Send/retrieve functions
@item
viossl.c -- SSL variations for the above
@item
viosslfactories.c -- Certification / Verification
@item
viotest.cc -- Short standalone test program: general
@item
viotest-ssl.c -- Short standalone test program: SSL
@item
viotest-sslconnect.cc -- Short standalone test program: SSL connect
@end itemize
@*@*
The older functions -- raw_net_read, raw_net_write -- are now
obsolete.
@*@*
@subsection zlib
Data compression library.
@*@*
Zlib -- which presumably stands for "Zip Library" -- is not a MySQL
package. It was produced by the GNU Zip (gzip.org) people. Zlib is a
variation of the famous "Lempel-Ziv" method, which is also used by
"Zip". The method for reducing the size of any arbitrary string of
bytes is as follows:
@itemize @bullet
@item
Find a substring which occurs twice in the string.
@item
Replace the second occurrence of the substring with (a) a pointer to
the first occurrence, plus (b) an indication of the length of the
first occurrence.
@end itemize
There is a full description of the library's functions in the gzip
manual at: @*
@url{http://www.gzip.org/zlib/manual.html} @*
There is therefore no need to list the modules in this document.
@*@*
The MySQL program that uses zlib is \mysys\my_compress.c. The use is
for packet compression. The client sends messages to the server which
are compressed by zlib. See also: \sql\net_serv.cc.
@node Files in InnoDB Sources,,Files in MySQL Sources,Top
@chapter Annotated List Of Files in the InnoDB Source Code Distribution
ERRATUM BY HEIKKI TUURI (START)
@*@*
Errata about InnoDB row locks:@*@*
@example
#define LOCK_S 4 /* shared */
#define LOCK_X 5 /* exclusive */
...
@strong{/* Waiting lock flag */}
#define LOCK_WAIT 256
/* this wait bit should be so high that it can be ORed to the lock
mode and type; when this bit is set, it means that the lock has not
yet been granted, it is just waiting for its turn in the wait queue */
...
@strong{/* Precise modes */}
#define LOCK_ORDINARY 0
/* this flag denotes an ordinary next-key lock in contrast to LOCK_GAP
or LOCK_REC_NOT_GAP */
#define LOCK_GAP 512
/* this gap bit should be so high that it can be ORed to the other
flags; when this bit is set, it means that the lock holds only on the
gap before the record; for instance, an x-lock on the gap does not
give permission to modify the record on which the bit is set; locks of
this type are created when records are removed from the index chain of
records */
#define LOCK_REC_NOT_GAP 1024
/* this bit means that the lock is only on the index record and does
NOT block inserts to the gap before the index record; this is used in
the case when we retrieve a record with a unique key, and is also used
in locking plain SELECTs (not part of UPDATE or DELETE) when the user
has set the READ COMMITTED isolation level */
#define LOCK_INSERT_INTENTION 2048
/* this bit is set when we place a waiting gap type record lock
request in order to let an insert of an index record to wait until
there are no conflicting locks by other transactions on the gap; note
that this flag remains set when the waiting lock is granted, or if the
lock is inherited to a neighboring record */
@end example
@*
ERRATUM BY HEIKKI TUURI (END)
@*@*
The InnoDB source files are the best place to look for information
about internals of the file structure that MySQLites can optionally
use for transaction support. But when you first look at all the
subdirectories and file names you'll wonder: Where Do I Start? It can
be daunting.
@*@*
Well, I've been through that phase, so I'll pass on what I had to
learn on the first day that I looked at InnoDB source files. I am very
sure that this will help you grasp, in overview, the organization of
InnoDB modules. I'm also going to add comments about what is going on
-- which you should mistrust! These comments are reasonable working
hypotheses; nevertheless, they have not been subjected to expert peer
review.
@*@*
Here's how I'm going to organize the discussion. I'll take each of the
32 InnoDB subdirectories that come with the MySQL 4.0 source code in
\mysql\innobase (on my Windows directory). The format of each section
will be like this every time:
@*@*
@strong{\subdirectory-name (LONGER EXPLANATORY NAME)}@*
@multitable @columnfractions .10 .20 .40 .50
@item @strong{File Name} @tab @strong{What Name Stands For} @tab @strong{Size} @tab @strong{Comment Inside File}
@item file-name
@tab my-own-guess
@tab in-bytes
@tab from-the-file-itself
@end multitable
...@*
My-Comments@*
@*
For example: @*
@example
"
@strong{\ha (HASHING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
ha0ha.c Hashing/Hashing 7,452 Hash table with external chains
Comments about hashing will be here.
"
@end example
@*
The "Comment Inside File" column is a direct copy from the first /*
comment */ line inside the file. All other comments are mine. After
I've discussed each directory, I'll finish with some notes about
naming conventions and a short list of URLs that you can use for
further reference.
@*@*
Now let's begin.
@*@*
@example
@strong{\ha (HASHING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
ha0ha.c Hashing / Hashing 7,452 Hash table with external chains
I'll hold my comments until the next section, \hash (HASHING).
@strong{\hash (HASHING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
hash0hash.c Hashing / Hashing 3,257 Simple hash table utility
The two C programs in the \ha and \hashing directories -- ha0ha.c and
hash0hash.c -- both refer to a "hash table" but hash0hash.c is
specialized, it is mostly about accessing points in the table under
mutex control.
When a "database" is so small that InnoDB can load it all into memory
at once, it's more efficient to access it via a hash table. After all,
no disk i/o can be saved by using an index lookup, if there's no disk.
@strong{\os (OPERATING SYSTEM)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
os0shm.c OS / Shared Memory 3,150 To shared memory primitives
os0file.c OS / File 64,412 To i/o primitives
os0thread.c OS / Thread 6,827 To thread control primitives
os0proc.c OS / Process 3,700 To process control primitives
os0sync.c OS / Synchronization 10,208 To synchronization primitives
This is a group of utilities that other modules may call whenever they
want to use an operating-system resource. For example, in os0file.c
there is a public InnoDB function named os_file_create_simple(), which
simply calls the Windows-API function CreateFile. Naturally the
contents of this group are somewhat different for other operating systems.
The "Shared Memory" functions in os0shm.c are only called from the
communications program com0shm.c (see \com COMMUNICATIONS). The i/o
and thread-control primitives are called extensively. The word
"synchronization" in this context refers to the mutex-create and
mutex-wait functionality.
@strong{\ut (UTILITIES)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
ut0ut.c Utilities / Utilities 7,041 Various utilities
ut0byte.c Utilities / Debug 1,856 Byte utilities
ut0rnd.c Utilities / Random 1,475 Random numbers and hashing
ut0mem.c Utilities / Memory 5,530 Memory primitives
ut0dbg.c Utilities / Debug 642 Debug utilities
The two functions in ut0byte.c are just for lower/upper case
conversion and comparison. The single function in ut0rnd.c is for
finding a prime slightly greater than the given argument, which is
useful for hash functions, but unrelated to randomness. The functions
in ut0mem.c are wrappers for "malloc" and "free" calls -- for the
real "memory" module see section \mem (MEMORY). Finally, the
functions in ut0ut.c are a miscellany that didn't fit better elsewhere:
get_high_bytes, clock, time, difftime, get_year_month_day, and "sprintf"
for various diagnostic purposes.
In short: the \ut group is trivial.
@strong{\buf (BUFFERING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
buf0buf.c Buffering / Buffering 53,246 The database buffer buf_pool
buf0flu.c Buffering / Flush 23,711 ... flush algorithm
buf0lru.c / least-recently-used 20,245 ... replacement algorithm
buf0rea.c Buffering / read 17,399 ... read
There is a separate file group (\mem MEMORY) which handles memory
requests in general.A "buffer" usually has a more specific
definition, as a memory area which contains copies of pages that
ordinarily are in the main data file. The "buffer pool" is the set
of all buffers (there are lots of them because InnoDB doesn't
depend on the OS's caching to make things faster).
The pool size is fixed (at the time of this writing) but the rest of
the buffering architecture is sophisticated, involving a host of
control structures. In general: when InnoDB needs to access a new page
it looks first in the buffer pool; InnoDB reads from disk to a new
buffer when the page isn't there; InnoDB chucks old buffers (basing
its decision on a conventional Least-Recently-Used algorithm) when it
has to make space for a new buffer.
There are routines for checking a page's validity, and for read-ahead.
An example of "read-ahead" use: if a sequential scan is going on, then
a DBMS can read more than one page at a time, which is efficient
because reading 32,768 bytes (two pages) takes less than twice as long
as reading 16,384 bytes (one page).
@strong{\btr (B-TREE)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
btr0btr.c B-tree / B-tree 74,255 B-tree
btr0cur.c B-tree / Cursor 94,950 index tree cursor
btr0sea.c B-tree / Search 36,580 index tree adaptive search
btr0pcur.c B-tree / persistent cursor 14,548 index tree persistent cursor
If you total up the sizes of the C files, you'll see that \btr is the
second-largest file group in InnoDB. This is understandable because
maintaining a B-tree is a relatively complex task. Luckily, there has
been a lot of work done to describe efficient management of B-tree and
B+-tree structures, much of it open-source or public-domain, since
their original invention over thirty years ago.
InnoDB likes to put everything in B-trees. This is what I'd call a
"distinguishing characteristic" because in all the major DBMSs (like
IBM DB2, Microsoft SQL Server, and Oracle), the main or default or
classic structure is the heap-and-index. In InnoDB the main structure
is just the index. To put it another way: InnoDB keeps the rows in the
leaf node of the index, rather than in a separate file. Compare
Oracle's Index Organized Tables, and Microsoft SQL Server's Clustered
Indexes.
This, by the way, has some consequences. For example, you may as well
have a primary key since otherwise InnoDB will make one anyway. And
that primary key should be the shortest of the candidate keys, since
InnoDB
will use it as a pointer if there are secondary indexes.
Most importantly, it means that rows have no fixed address. Therefore
the routines for managing file pages should be good. We'll see about
that when we look at the \row (ROW) program group later.
@strong{\com (COMMUNCATION)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
com0com.c Communication 6,913 Communication primitives
com0shm.c Communication / 24,633 ... through shared memory
Shared Memory
The communication primitives in com0com.c are said to be modelled
after the ones in Microsoft's winsock library (the Windows Sockets
interface). The communication primitives in com0shm.c are at a
slightly lower level, and are called from the routines in com0com.c.
I was interested in seeing how InnoDB would handle inter-process
communication, since there are many options -- named pipes, TCP/IP,
Windows messaging, and Shared Memory being the main ones that come to
mind. It appears that InnoDB prefers Shared Memory. The main idea is:
there is an area of memory which two different processes (or threads,
of course) can both access. To communicate, a thread gets an
appropriate mutex, puts in a request, and waits for a response. Thread
interaction is also a subject for the os0thread.c program in another
program group, \os (OPERATING SYSTEM).
@strong{\dyn (DYNAMICALLY ALLOCATED ARRAY)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
dyn0dyn.c Dynamic / Dynamic 994 dynamically allocated array
There is a single function in the dyn0dyn.c program, for adding a
block to the dynamically allocated array. InnoDB might use the array
for managing concurrency between threads.
At the moment, the \dyn program group is trivial.
@strong{\fil (FILE)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
fil0fil.c File / File 39,725 The low-level file system
The reads and writes to the database files happen here, in
co-ordination with the low-level file i/o routines (see os0file.h in
the \os program group).
Briefly: a table's contents are in pages, which are in files, which
are in tablespaces. Files do not grow; instead one can add new files
to the tablespace. As we saw earlier (discussing the \btr program group)
the pages are nodes of B-trees. Since that's the case, new additions can
happen at various places in the logical file structure, not
necessarily at the end. Reads and writes are asynchronous, and go into
buffers, which are set up by routines in the \buf program group.
@strong{\fsp (FILE SPACE)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
fsp0fsp.c File Space Management 100,271 File space management
I would have thought that the \fil (FILE) and \fsp (FILE SPACE)
MANAGEMENT programs would fit together in the same program group;
however, I guess the InnoDB folk are splitters rather than lumpers.
It's in fsp0fsp.c that one finds some of the descriptions and comments
of extents, segments, and headers. For example, the "descriptor bitmap
of the pages in the extent" is in here, and you can find as well how
the free-page list is maintained, what's in the bitmaps, and what
various header fields' contents are.
@strong{\fut (FILE UTILITY)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
fut0fut.c File Utility / Utility 293 File-based utilities
fut0lst.c File Utility / List 14,129 File-based list utilities
Mainly these small programs affect only file-based lists, so maybe
saying "File Utility" is too generic. The real work with data files
goes on in the \fsp program group.
@strong{\log (LOGGING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
log0log.c Logging / Logging 77,834 Database log
log0recv.c Logging / Recovery 80,701 Recovery
I've already written about the \log program group, so here's a link to
my previous article: "How Logs work with MySQL and InnoDB":
@url{http://www.devarticles.com/art/1/181/2}
@strong{\mem (MEMORY)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
mem0mem.c Memory / Memory 9,971 The memory management
mem0dbg.c Memory / Debug 21,297 ... the debug code
mem0pool.c Memory / Pool 16,293 ... the lowest level
There is a long comment at the start of the mem0pool.c program, which
explains what the memory-consumers are, and how InnoDB tries to
satisfy them. The main thing to know is that there are really three
pools: the buffer pool (see the \buf program group), the log pool (see the \log
program group), and the common pool, which is where everything that's
not in the buffer or log pools goes (for example the parsed SQL
statements and the data dictionary cache).
@strong{\mtr (MINI-TRANSACTION)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
mtr0mtr.c Mini-transaction / 12,433 Mini-transaction buffer
mtr0log.c Mini-transaction / Log 8,180 ... log routines
The mini-transaction routines are called from most of the other
program groups. I'd describe this as a low-level utility set.
@strong{\que (QUERY GRAPH)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
que0que.c Query Graph / Query 35,964 Query graph
The program que0que.c ostensibly is about the execution of stored
procedures which contain commit/rollback statements. I took it that
this has little importance for the average MySQL user.
@strong{\rem (RECORD MANAGER)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
rem0rec.c Record Manager 14,961 Record Manager
rem0cmp.c Record Manager / 25,263 Comparison services for records
Comparison
There's an extensive comment near the start of rem0rec.c title
"Physical Record" and it's recommended reading. At some point you'll
ask what are all those bits that surround the data in the rows on a page,
and this is where you'll find the answer.
@strong{\row (ROW)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
row0row.c Row / Row 16,764 General row routines
row0uins.c Row / Undo Insert 7,199 Fresh insert undo
row0umod.c Row / Undo Modify 17,147 Undo modify of a row
row0undo.c Row / Undo 10,254 Row undo
row0vers.c Row / Version 12,288 Row versions
row0mysql.c Row / MySQL 63,556 Interface [to MySQL]
row0ins.c Row / Insert 42,829 Insert into a table
row0sel.c Row / Select 85,923 Select
row0upd.c Row / Update 44,456 Update of a row
row0purge.c Row / Purge 14,961 Purge obsolete records
Rows can be selected, inserted, updated/deleted, or purged (a
maintenance activity). These actions have ancillary actions, for
example after insert there can be an index-update test, but it seems
to me that sometimes the ancillary action has no MySQL equivalent (yet)
and so is inoperative.
Speaking of MySQL, notice that one of the larger programs in the \row
program group is the "interface between Innobase row operations and
MySQL" (row0mysql.c) -- information interchange happens at this level
because rows in InnoDB and in MySQL are analogous, something which
can't be said for pages and other levels.
@strong{\srv (Server)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
srv0srv.c Server / Server 79,058 Server main program
srv0que.c Server / Query 2,361 Server query execution
srv0start.c Server / Start 34,586 Starts the server
This is where the server reads the initial configuration files, splits
up the threads, and gets going. There is a long comment deep in the
program (you might miss it at first glance) titled "IMPLEMENTATION OF
THE SERVER MAIN PROGRAM" in which you'll find explanations about
thread priority, and about what the responsibiities are for various
thread types.
InnoDB has many threads, for example "user threads" (which wait for
client requests and reply to them), "parallel communication threads"
(which take part of a user thread's job if a query process can be
split), "utility threads" (background priority), and a "master thread"
(high priority, usually asleep).
@strong{\thr (Thread Local Storage)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
thr0loc.c Thread / Local 5,261 The thread local storage
InnoDB doesn't use the Windows-API thread-local-storage functions,
perhaps because they're not portable enough.
@strong{\trx (Transaction)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
trx0trx.c Transaction / 37,447 The transaction
trx0purge.c Transaction / Purge 26,782 ... Purge old versions
trx0rec.c Transaction / Record 36,525 ... Undo log record
trx0sys.c Transaction / System 20,671 ... System
trx0rseg.c / Rollback segment 6,214 ... Rollback segment
trx0undo.c Transaction / Undo 46,595 ... Undo log
InnoDB's transaction management is supposedly "in the style of Oracle"
and that's close to true but can mislead you.
@itemize
@item
First: InnoDB uses rollback segments like Oracle8i does -- but
Oracle9i uses a different name
@item
Second: InnoDB uses multi-versioning like Oracle does -- but I see
nothing that looks like an Oracle ITL being stored in the InnoDB data
pages.
@item
Third: InnoDB and Oracle both have short (back-to-statement-start)
versioning for the READ COMMITTED isolation level and long
(back-to-transaction-start) versioning for higher levels -- but InnoDB
and Oracle have different "default" isolation levels.
@item
Finally: InnoDB's documentation says it has to lock "the gaps before
index keys" to prevent phantoms -- but any Oracle user will tell you that
phantoms are impossible anyway at the SERIALIZABLE isolation level, so
key-locks are unnecessary.
@end itemize
The main idea, though, is that InnoDB has multi-versioning. So does
Oracle. This is very different from the way that DB2 and SQL Server do
things.
@strong{\usr (USER)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
usr0sess.c User / Session 27,415 Sessions
One user can have multiple sessions (the session being all the things
that happen betweeen a connect and disconnect). This is where InnoDB
tracks session IDs, and server/client messaging. It's another of those
items which is usually MySQL's job, though.
@strong{\data (DATA)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
data0data.c Data / Data 26,002 SQL data field and tuple
data0type.c Data / Type 2,122 Data types
This is a collection of minor utility routines affecting rows.
@strong{\dict (DICTIONARY)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
dict0dict.c Dictionary / Dictionary 84,667 Data dictionary system
dict0boot.c Dictionary / boot 12,134 ... creation and booting
dict0load.c Dictionary / load 26,546 ... load to memory cache
dict0mem.c Dictionary / memory 8,221 ... memory object creation
The data dictionary (known in some circles as the catalog) has the
metadata information about objects in the database -- column sizes,
table names, and the like.
@strong{\eval (EVALUATING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
eval0eval.c Evaluating/Evaluating 15,682 SQL evaluator
eval0proc.c Evaluating/Procedures 5,000 Executes SQL procedures
The evaluating step is a late part of the process of interpreting an
SQL statement -- parsing has already occurred during \pars (PARSING).
The ability to execute SQL stored procedures is an InnoDB feature, but
not a MySQL feature, so the eval0proc.c program is unimportant.
@strong{\ibuf (INSERT BUFFER)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
ibuf0ibuf.c Insert Buffer / 69,884 Insert buffer
The words "Insert Buffer" mean not "buffer used for INSERT" but
"insertion of a buffer into the buffer pool" (see the \buf BUFFER
program group description). The matter is complex due to possibilities
for deadlocks, a problem to which the comments in the ibuf0ibuf.c
program devote considerable attention.
@strong{\mach (MACHINE FORMAT)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
mach0data.c Machine/Data 2,319 Utilities for converting
The mach0data.c program has two small routines for reading compressed
ulints (unsigned long integers).
@strong{\lock (LOCKING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
lock0lock.c Lock / Lock 127,646 The transaction lock system
If you've used DB2 or SQL Server, you might think that locks have their
own in-memory table, that row locks might need occasional escalation to
table locks, and that there are three lock types: Shared, Update, Exclusive.
All those things are untrue with InnoDB! Locks are kept in the database
pages. A bunch of row locks can't be rolled together into a single table
lock. And most importantly there's only one lock type. I call this type
"Update" because it has the characteristics of DB2 / SQL Server Update
locks, that is, it blocks other updates but doesn't block reads.
Unfortunately, InnoDB comments refer to them as "x-locks" etc.
To sum it up: if your background is Oracle you won't find too much
surprising, but if your background is DB2 or SQL Server the locking
concepts and terminology will probably confuse you at first.
You can find an online article about the differences between
Oracle-style and DB2/SQL-Server-style locks at:
@url{http://dbazine.com/gulutzan6.html}
@strong{\odbc (ODBC)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
odbc0odbc.c ODBC / ODBC 16,865 ODBC client library
The odbc0odbc.c program has a small selection of old ODBC-API
functions: SQLAllocEnv, SQLAllocConnect, SQLAllocStmt, SQLConnect,
SQLError, SQLPrepare, SQLBindParameter, SQLExecute.
@strong{\page (PAGE)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
page0page.c Page / Page 44,309 Index page routines
page0cur.c Page / Cursor 30,305 The page cursor
It's in the page0page.c program that you'll learn as follows: index
pages start with a header, entries in the page are in order, at the
end of the page is a sparse "page directory" (what I would have called
a slot table) which makes binary searches easier.
Incidentally, the program comments refer to "a page size of 8 kB"
which seems obsolete. In univ.i (a file containing universal
constants) the page size is now #defined as 16KB.
@strong{\pars (PARSING)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
pars0pars.c Parsing/Parsing 49,947 SQL parser
pars0grm.c Parsing/Grammar 62,685 A Bison parser
pars0opt.c Parsing/Optimizer 30,809 Simple SQL Optimizer
pars0sym.c Parsing/Symbol Table 5,541 SQL parser symbol table
lexyy.c ?/Lexer 59,948 Lexical scanner
The job is to input a string containing an SQL statement and output an
in-memory parse tree. The EVALUATING (subdirectory \eval) programs
will use the tree.
As is common practice, the Bison and Flex tools were used -- pars0grm.c
is what the Bison parser produced from an original file named pars0grm.y
(not supplied), and lexyy.c is what Flex produced.
Since InnoDB is a DBMS by itself, it's natural to find SQL parsing in
it. But in the MySQL/InnoDB combination, MySQL handles most of the
parsing. These files are unimportant.
@strong{\read (READ)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
read0read.c Read / Read 6,244 Cursor read
The read0read.c program opens a "read view" of a query result, using
some functions in the \trx program group.
@strong{\sync (SYNCHRONIZATION)}
File Name What Name Stands For Size Comment Inside File
--------- -------------------- ------ -------------------
sync0sync.c Synchronization / 35,918 Mutex, the basic sync primitive
sync0arr.c ... / array 26,461 Wait array used in primitives
sync0ipm.c ... / interprocess 4,027 for interprocess sync
sync0rw.c ... / read-write 22,220 read-write lock for thread sync
A mutex (Mutual Exclusion) is an object which only one thread/process
can hold at a time. Any modern operating system API has some functions
for mutexes; however, as the comments in the sync0sync.c code indicate, it
can be faster to write one's own low-level mechanism. In fact the old
assembly-language XCHG trick is in here -- this is the only program
that contains any assembly code.
@end example
@*
@*
This is the end of the section-by-section account of InnoDB
subdirectories.
@*@*
@strong{A Note About File Naming} @*@*
There appears to be a naming convention. The first letters of the file
name are the same as the subdirectory name, then there is a '0'
separator, then there is an individual name. For the main program in a
subdirectory, the individual name may be a repeat of the subdirectory
name. For example, there is a file named ha0ha.c (the first two
letters ha mean "it's in in subdirectory ..\ha", the next letter 0
means "0 separator", the next two letters mean "this is the main ha
program"). This naming convention is not strict, though: for example
the file lexyy.c is in the \pars subdirectory.
@*@*
@strong{A Note About Copyrights} @*@*
Most of the files begin with a copyright notice or a creation date,
for example "Created 10/25/1995 Heikki Tuuri". I don't know a great
deal about the history of InnoDB, but found it interesting that most
creation dates were between 1994 and 1998.
@*@*
@strong{References} @*@*
Ryan Bannon, Alvin Chin, Faryaaz Kassam and Andrew Roszko @*
"InnoDB Concrete Architecture" @*
@url{http://www.swen.uwaterloo.ca/~mrbannon/cs798/assignment_02/innodb.pdf}
A student paper. It's an interesting attempt to figure out InnoDB's
architecture using tools, but I didn't end up using it for the specific
purposes of this article.
@*@*
Peter Gulutzan @*
"How Logs Work With MySQL And InnoDB" @*
@url{http://www.devarticles.com/art/1/181/2}
@*@*
Heikki Tuuri @*
"InnoDB Engine in MySQL-Max-3.23.54 / MySQL-4.0.9: The Up-to-Date
Reference Manual of InnoDB" @*
@url{http://www.innodb.com/ibman.html}
This is the natural starting point for all InnoDB information. Mr
Tuuri also appears frequently on MySQL forums.
@*@*
@summarycontents
@contents
@bye
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