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mariadb/Docs/internals.texi
unknown 1543bad3e7 Fix for bug in LOAD DATA INFILE and replication 
Fix for SHOW VARIABLES in embedded server


Docs/internals.texi:
  Added documentation for join_buffer_size
configure.in:
  Changed version number
sql/log_event.cc:
  Fix for bug in LOAD DATA INFILE
sql/log_event.h:
  Fix for bug in LOAD DATA INFILE
sql/slave.cc:
  Fix for bug in LOAD DATA INFILE
sql/sql_show.cc:
  Fix for SHOW VARIABLES in embedded server
2003-01-08 11:24:39 +02:00

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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
* flush tables:: How MySQL Handles @code{FLUSH TABLES}
* filesort:: How MySQL Does Sorting (@code{filesort})
* 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
@end menu
@node caching, flush tables, 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
@subchapter 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, caching, 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, coding guidelines, 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 coding guidelines, mysys functions, filesort, 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
@node 4.1 protocol,,,
@subchapter 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 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 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 itemize
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 descr}.
@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 itemize
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 itemize
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, , 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.
@summarycontents
@contents
@bye
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