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mariadb/storage/example/ha_example.cc
monty@mysql.com 74cc73d461 This changeset is largely a handler cleanup changeset (WL#3281), but includes fixes and cleanups that was found necessary while testing the handler changes 
Changes that requires code changes in other code of other storage engines.
(Note that all changes are very straightforward and one should find all issues
by compiling a --debug build and fixing all compiler errors and all
asserts in field.cc while running the test suite),

- New optional handler function introduced: reset()
  This is called after every DML statement to make it easy for a handler to
  statement specific cleanups.
  (The only case it's not called is if force the file to be closed)

- handler::extra(HA_EXTRA_RESET) is removed. Code that was there before
  should be moved to handler::reset()

- table->read_set contains a bitmap over all columns that are needed
  in the query.  read_row() and similar functions only needs to read these
  columns
- table->write_set contains a bitmap over all columns that will be updated
  in the query. write_row() and update_row() only needs to update these
  columns.
  The above bitmaps should now be up to date in all context
  (including ALTER TABLE, filesort()).

  The handler is informed of any changes to the bitmap after
  fix_fields() by calling the virtual function
  handler::column_bitmaps_signal(). If the handler does caching of
  these bitmaps (instead of using table->read_set, table->write_set),
  it should redo the caching in this code. as the signal() may be sent
  several times, it's probably best to set a variable in the signal
  and redo the caching on read_row() / write_row() if the variable was
  set.

- Removed the read_set and write_set bitmap objects from the handler class

- Removed all column bit handling functions from the handler class.
  (Now one instead uses the normal bitmap functions in my_bitmap.c instead
  of handler dedicated bitmap functions)

- field->query_id is removed. One should instead instead check
  table->read_set and table->write_set if a field is used in the query.

- handler::extra(HA_EXTRA_RETRIVE_ALL_COLS) and
  handler::extra(HA_EXTRA_RETRIEVE_PRIMARY_KEY) are removed. One should now
  instead use table->read_set to check for which columns to retrieve.

- If a handler needs to call Field->val() or Field->store() on columns
  that are not used in the query, one should install a temporary
  all-columns-used map while doing so. For this, we provide the following
  functions:

  my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->read_set);
  field->val();
  dbug_tmp_restore_column_map(table->read_set, old_map);

  and similar for the write map:

  my_bitmap_map *old_map= dbug_tmp_use_all_columns(table, table->write_set);
  field->val();
  dbug_tmp_restore_column_map(table->write_set, old_map);

  If this is not done, you will sooner or later hit a DBUG_ASSERT
  in the field store() / val() functions.
  (For not DBUG binaries, the dbug_tmp_restore_column_map() and
  dbug_tmp_restore_column_map() are inline dummy functions and should
  be optimized away be the compiler).

- If one needs to temporary set the column map for all binaries (and not
  just to avoid the DBUG_ASSERT() in the Field::store() / Field::val()
  methods) one should use the functions tmp_use_all_columns() and
  tmp_restore_column_map() instead of the above dbug_ variants.

- All 'status' fields in the handler base class (like records,
  data_file_length etc) are now stored in a 'stats' struct. This makes
  it easier to know what status variables are provided by the base
  handler.  This requires some trivial variable names in the extra()
  function.

- New virtual function handler::records().  This is called to optimize
  COUNT(*) if (handler::table_flags() & HA_HAS_RECORDS()) is true.
  (stats.records is not supposed to be an exact value. It's only has to
  be 'reasonable enough' for the optimizer to be able to choose a good
  optimization path).

- Non virtual handler::init() function added for caching of virtual
  constants from engine.

- Removed has_transactions() virtual method. Now one should instead return
  HA_NO_TRANSACTIONS in table_flags() if the table handler DOES NOT support
  transactions.

- The 'xxxx_create_handler()' function now has a MEM_ROOT_root argument
  that is to be used with 'new handler_name()' to allocate the handler
  in the right area.  The xxxx_create_handler() function is also
  responsible for any initialization of the object before returning.

  For example, one should change:

  static handler *myisam_create_handler(TABLE_SHARE *table)
  {
    return new ha_myisam(table);
  }

  ->

  static handler *myisam_create_handler(TABLE_SHARE *table, MEM_ROOT *mem_root)
  {
    return new (mem_root) ha_myisam(table);
  }

- New optional virtual function: use_hidden_primary_key().
  This is called in case of an update/delete when
  (table_flags() and HA_PRIMARY_KEY_REQUIRED_FOR_DELETE) is defined
  but we don't have a primary key. This allows the handler to take precisions
  in remembering any hidden primary key to able to update/delete any
  found row. The default handler marks all columns to be read.

- handler::table_flags() now returns a ulonglong (to allow for more flags).

- New/changed table_flags()
  - HA_HAS_RECORDS	    Set if ::records() is supported
  - HA_NO_TRANSACTIONS	    Set if engine doesn't support transactions
  - HA_PRIMARY_KEY_REQUIRED_FOR_DELETE
                            Set if we should mark all primary key columns for
			    read when reading rows as part of a DELETE
			    statement. If there is no primary key,
			    all columns are marked for read.
  - HA_PARTIAL_COLUMN_READ  Set if engine will not read all columns in some
			    cases (based on table->read_set)
 - HA_PRIMARY_KEY_ALLOW_RANDOM_ACCESS
   			    Renamed to HA_PRIMARY_KEY_REQUIRED_FOR_POSITION.
 - HA_DUPP_POS              Renamed to HA_DUPLICATE_POS
 - HA_REQUIRES_KEY_COLUMNS_FOR_DELETE
			    Set this if we should mark ALL key columns for
			    read when when reading rows as part of a DELETE
			    statement. In case of an update we will mark
			    all keys for read for which key part changed
			    value.
  - HA_STATS_RECORDS_IS_EXACT
			     Set this if stats.records is exact.
			     (This saves us some extra records() calls
			     when optimizing COUNT(*))
			    

- Removed table_flags()
  - HA_NOT_EXACT_COUNT     Now one should instead use HA_HAS_RECORDS if
			   handler::records() gives an exact count() and
			   HA_STATS_RECORDS_IS_EXACT if stats.records is exact.
  - HA_READ_RND_SAME	   Removed (no one supported this one)

- Removed not needed functions ha_retrieve_all_cols() and ha_retrieve_all_pk()

- Renamed handler::dupp_pos to handler::dup_pos

- Removed not used variable handler::sortkey


Upper level handler changes:

- ha_reset() now does some overall checks and calls ::reset()
- ha_table_flags() added. This is a cached version of table_flags(). The
  cache is updated on engine creation time and updated on open.


MySQL level changes (not obvious from the above):

- DBUG_ASSERT() added to check that column usage matches what is set
  in the column usage bit maps. (This found a LOT of bugs in current
  column marking code).

- In 5.1 before, all used columns was marked in read_set and only updated
  columns was marked in write_set. Now we only mark columns for which we
  need a value in read_set.

- Column bitmaps are created in open_binary_frm() and open_table_from_share().
  (Before this was in table.cc)

- handler::table_flags() calls are replaced with handler::ha_table_flags()

- For calling field->val() you must have the corresponding bit set in
  table->read_set. For calling field->store() you must have the
  corresponding bit set in table->write_set. (There are asserts in
  all store()/val() functions to catch wrong usage)

- thd->set_query_id is renamed to thd->mark_used_columns and instead
  of setting this to an integer value, this has now the values:
  MARK_COLUMNS_NONE, MARK_COLUMNS_READ, MARK_COLUMNS_WRITE
  Changed also all variables named 'set_query_id' to mark_used_columns.

- In filesort() we now inform the handler of exactly which columns are needed
  doing the sort and choosing the rows.

- The TABLE_SHARE object has a 'all_set' column bitmap one can use
  when one needs a column bitmap with all columns set.
  (This is used for table->use_all_columns() and other places)

- The TABLE object has 3 column bitmaps:
  - def_read_set     Default bitmap for columns to be read
  - def_write_set    Default bitmap for columns to be written
  - tmp_set          Can be used as a temporary bitmap when needed.
  The table object has also two pointer to bitmaps read_set and write_set
  that the handler should use to find out which columns are used in which way.

- count() optimization now calls handler::records() instead of using
  handler->stats.records (if (table_flags() & HA_HAS_RECORDS) is true).

- Added extra argument to Item::walk() to indicate if we should also
  traverse sub queries.

- Added TABLE parameter to cp_buffer_from_ref()

- Don't close tables created with CREATE ... SELECT but keep them in
  the table cache. (Faster usage of newly created tables).


New interfaces:

- table->clear_column_bitmaps() to initialize the bitmaps for tables
  at start of new statements.

- table->column_bitmaps_set() to set up new column bitmaps and signal
  the handler about this.

- table->column_bitmaps_set_no_signal() for some few cases where we need
  to setup new column bitmaps but don't signal the handler (as the handler
  has already been signaled about these before). Used for the momement
  only in opt_range.cc when doing ROR scans.

- table->use_all_columns() to install a bitmap where all columns are marked
  as use in the read and the write set.

- table->default_column_bitmaps() to install the normal read and write
  column bitmaps, but not signaling the handler about this.
  This is mainly used when creating TABLE instances.

- table->mark_columns_needed_for_delete(),
  table->mark_columns_needed_for_delete() and
  table->mark_columns_needed_for_insert() to allow us to put additional
  columns in column usage maps if handler so requires.
  (The handler indicates what it neads in handler->table_flags())

- table->prepare_for_position() to allow us to tell handler that it
  needs to read primary key parts to be able to store them in
  future table->position() calls.
  (This replaces the table->file->ha_retrieve_all_pk function)

- table->mark_auto_increment_column() to tell handler are going to update
  columns part of any auto_increment key.

- table->mark_columns_used_by_index() to mark all columns that is part of
  an index.  It will also send extra(HA_EXTRA_KEYREAD) to handler to allow
  it to quickly know that it only needs to read colums that are part
  of the key.  (The handler can also use the column map for detecting this,
  but simpler/faster handler can just monitor the extra() call).

- table->mark_columns_used_by_index_no_reset() to in addition to other columns,
  also mark all columns that is used by the given key.

- table->restore_column_maps_after_mark_index() to restore to default
  column maps after a call to table->mark_columns_used_by_index().

- New item function register_field_in_read_map(), for marking used columns
  in table->read_map. Used by filesort() to mark all used columns

- Maintain in TABLE->merge_keys set of all keys that are used in query.
  (Simplices some optimization loops)

- Maintain Field->part_of_key_not_clustered which is like Field->part_of_key
  but the field in the clustered key is not assumed to be part of all index.
  (used in opt_range.cc for faster loops)

-  dbug_tmp_use_all_columns(), dbug_tmp_restore_column_map()
   tmp_use_all_columns() and tmp_restore_column_map() functions to temporally
   mark all columns as usable.  The 'dbug_' version is primarily intended
   inside a handler when it wants to just call Field:store() & Field::val()
   functions, but don't need the column maps set for any other usage.
   (ie:: bitmap_is_set() is never called)

- We can't use compare_records() to skip updates for handlers that returns
  a partial column set and the read_set doesn't cover all columns in the
  write set. The reason for this is that if we have a column marked only for
  write we can't in the MySQL level know if the value changed or not.
  The reason this worked before was that MySQL marked all to be written
  columns as also to be read. The new 'optimal' bitmaps exposed this 'hidden
  bug'.

- open_table_from_share() does not anymore setup temporary MEM_ROOT
  object as a thread specific variable for the handler. Instead we
  send the to-be-used MEMROOT to get_new_handler().
  (Simpler, faster code)



Bugs fixed:

- Column marking was not done correctly in a lot of cases.
  (ALTER TABLE, when using triggers, auto_increment fields etc)
  (Could potentially result in wrong values inserted in table handlers
  relying on that the old column maps or field->set_query_id was correct)
  Especially when it comes to triggers, there may be cases where the
  old code would cause lost/wrong values for NDB and/or InnoDB tables.

- Split thd->options flag OPTION_STATUS_NO_TRANS_UPDATE to two flags:
  OPTION_STATUS_NO_TRANS_UPDATE and OPTION_KEEP_LOG.
  This allowed me to remove some wrong warnings about:
  "Some non-transactional changed tables couldn't be rolled back"

- Fixed handling of INSERT .. SELECT and CREATE ... SELECT that wrongly reset
  (thd->options & OPTION_STATUS_NO_TRANS_UPDATE) which caused us to loose
  some warnings about
  "Some non-transactional changed tables couldn't be rolled back")

- Fixed use of uninitialized memory in ha_ndbcluster.cc::delete_table()
  which could cause delete_table to report random failures.

- Fixed core dumps for some tests when running with --debug

- Added missing FN_LIBCHAR in mysql_rm_tmp_tables()
  (This has probably caused us to not properly remove temporary files after
  crash)

- slow_logs was not properly initialized, which could maybe cause
  extra/lost entries in slow log.

- If we get an duplicate row on insert, change column map to read and
  write all columns while retrying the operation. This is required by
  the definition of REPLACE and also ensures that fields that are only
  part of UPDATE are properly handled.  This fixed a bug in NDB and
  REPLACE where REPLACE wrongly copied some column values from the replaced
  row.

- For table handler that doesn't support NULL in keys, we would give an error
  when creating a primary key with NULL fields, even after the fields has been
  automaticly converted to NOT NULL.

- Creating a primary key on a SPATIAL key, would fail if field was not
  declared as NOT NULL.


Cleanups:

- Removed not used condition argument to setup_tables

- Removed not needed item function reset_query_id_processor().

- Field->add_index is removed. Now this is instead maintained in
  (field->flags & FIELD_IN_ADD_INDEX)

- Field->fieldnr is removed (use field->field_index instead)

- New argument to filesort() to indicate that it should return a set of
  row pointers (not used columns). This allowed me to remove some references
  to sql_command in filesort and should also enable us to return column
  results in some cases where we couldn't before.

- Changed column bitmap handling in opt_range.cc to be aligned with TABLE
  bitmap, which allowed me to use bitmap functions instead of looping over
  all fields to create some needed bitmaps. (Faster and smaller code)

- Broke up found too long lines

- Moved some variable declaration at start of function for better code
  readability.

- Removed some not used arguments from functions.
  (setup_fields(), mysql_prepare_insert_check_table())

- setup_fields() now takes an enum instead of an int for marking columns
   usage.

- For internal temporary tables, use handler::write_row(),
  handler::delete_row() and handler::update_row() instead of
  handler::ha_xxxx() for faster execution.

- Changed some constants to enum's and define's.

- Using separate column read and write sets allows for easier checking
  of timestamp field was set by statement.

- Remove calls to free_io_cache() as this is now done automaticly in ha_reset()

- Don't build table->normalized_path as this is now identical to table->path
  (after bar's fixes to convert filenames)

- Fixed some missed DBUG_PRINT(.."%lx") to use "0x%lx" to make it easier to
  do comparision with the 'convert-dbug-for-diff' tool.


Things left to do in 5.1:

- We wrongly log failed CREATE TABLE ... SELECT in some cases when using
  row based logging (as shown by testcase binlog_row_mix_innodb_myisam.result)
  Mats has promised to look into this.

- Test that my fix for CREATE TABLE ... SELECT is indeed correct.
  (I added several test cases for this, but in this case it's better that
  someone else also tests this throughly).
  Lars has promosed to do this.
2006-06-04 18:52:22 +03:00

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/* Copyright (C) 2003 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/*
ha_example is a stubbed storage engine. It does nothing at this point. It
will let you create/open/delete tables but that is all. You can enable it
in your buld by doing the following during your build process:
./configure --with-example-storage-engine
Once this is done mysql will let you create tables with:
CREATE TABLE A (...) ENGINE=EXAMPLE;
The example is setup to use table locks. It implements an example "SHARE"
that is inserted into a hash by table name. You can use this to store
information of state that any example handler object will be able to see
if it is using the same table.
Please read the object definition in ha_example.h before reading the rest
if this file.
To get an idea of what occurs here is an example select that would do a
scan of an entire table:
ha_example::store_lock
ha_example::external_lock
ha_example::info
ha_example::rnd_init
ha_example::extra
ENUM HA_EXTRA_CACHE Cash record in HA_rrnd()
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::rnd_next
ha_example::extra
ENUM HA_EXTRA_NO_CACHE End cacheing of records (def)
ha_example::external_lock
ha_example::extra
ENUM HA_EXTRA_RESET Reset database to after open
In the above example has 9 row called before rnd_next signalled that it was
at the end of its data. In the above example the table was already opened
(or you would have seen a call to ha_example::open(). Calls to
ha_example::extra() are hints as to what will be occuring to the request.
Happy coding!
-Brian
*/
#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation // gcc: Class implementation
#endif
#include "mysql_priv.h"
#include "ha_example.h"
#include <mysql/plugin.h>
static handler *example_create_handler(TABLE_SHARE *table, MEM_ROOT *mem_root);
static int example_init_func();
static bool example_init_func_for_handlerton();
static int example_panic(enum ha_panic_function flag);
static const char example_hton_name[]= "EXAMPLE";
static const char example_hton_comment[]= "Example storage engine";
handlerton example_hton= {
MYSQL_HANDLERTON_INTERFACE_VERSION,
example_hton_name,
SHOW_OPTION_YES,
example_hton_comment,
DB_TYPE_EXAMPLE_DB,
example_init_func_for_handlerton,
0, /* slot */
0, /* savepoint size. */
NULL, /* close_connection */
NULL, /* savepoint */
NULL, /* rollback to savepoint */
NULL, /* release savepoint */
NULL, /* commit */
NULL, /* rollback */
NULL, /* prepare */
NULL, /* recover */
NULL, /* commit_by_xid */
NULL, /* rollback_by_xid */
NULL, /* create_cursor_read_view */
NULL, /* set_cursor_read_view */
NULL, /* close_cursor_read_view */
example_create_handler, /* Create a new handler */
NULL, /* Drop a database */
example_panic, /* Panic call */
NULL, /* Start Consistent Snapshot */
NULL, /* Flush logs */
NULL, /* Show status */
NULL, /* Partition flags */
NULL, /* Alter table flags */
NULL, /* Alter tablespace */
NULL, /* Fill Files table */
HTON_CAN_RECREATE,
NULL,
NULL,
NULL,
};
/* Variables for example share methods */
static HASH example_open_tables; // Hash used to track open tables
pthread_mutex_t example_mutex; // This is the mutex we use to init the hash
static int example_init= 0; // Variable for checking the init state of hash
/*
Function we use in the creation of our hash to get key.
*/
static byte* example_get_key(EXAMPLE_SHARE *share,uint *length,
my_bool not_used __attribute__((unused)))
{
*length=share->table_name_length;
return (byte*) share->table_name;
}
static int example_init_func()
{
DBUG_ENTER("example_init_func");
if (!example_init)
{
example_init= 1;
VOID(pthread_mutex_init(&example_mutex,MY_MUTEX_INIT_FAST));
(void) hash_init(&example_open_tables,system_charset_info,32,0,0,
(hash_get_key) example_get_key,0,0);
}
DBUG_RETURN(0);
}
static int example_done_func()
{
int error= 0;
DBUG_ENTER("example_done_func");
if (example_init)
{
example_init= 0;
if (example_open_tables.records)
error= 1;
hash_free(&example_open_tables);
pthread_mutex_destroy(&example_mutex);
}
DBUG_RETURN(0);
}
static bool example_init_func_for_handlerton()
{
return example_init_func();
}
static int example_panic(enum ha_panic_function flag)
{
return example_done_func();
}
/*
Example of simple lock controls. The "share" it creates is structure we will
pass to each example handler. Do you have to have one of these? Well, you have
pieces that are used for locking, and they are needed to function.
*/
static EXAMPLE_SHARE *get_share(const char *table_name, TABLE *table)
{
EXAMPLE_SHARE *share;
uint length;
char *tmp_name;
pthread_mutex_lock(&example_mutex);
length=(uint) strlen(table_name);
if (!(share=(EXAMPLE_SHARE*) hash_search(&example_open_tables,
(byte*) table_name,
length)))
{
if (!(share=(EXAMPLE_SHARE *)
my_multi_malloc(MYF(MY_WME | MY_ZEROFILL),
&share, sizeof(*share),
&tmp_name, length+1,
NullS)))
{
pthread_mutex_unlock(&example_mutex);
return NULL;
}
share->use_count=0;
share->table_name_length=length;
share->table_name=tmp_name;
strmov(share->table_name,table_name);
if (my_hash_insert(&example_open_tables, (byte*) share))
goto error;
thr_lock_init(&share->lock);
pthread_mutex_init(&share->mutex,MY_MUTEX_INIT_FAST);
}
share->use_count++;
pthread_mutex_unlock(&example_mutex);
return share;
error:
pthread_mutex_destroy(&share->mutex);
my_free((gptr) share, MYF(0));
return NULL;
}
/*
Free lock controls. We call this whenever we close a table. If the table had
the last reference to the share then we free memory associated with it.
*/
static int free_share(EXAMPLE_SHARE *share)
{
pthread_mutex_lock(&example_mutex);
if (!--share->use_count)
{
hash_delete(&example_open_tables, (byte*) share);
thr_lock_delete(&share->lock);
pthread_mutex_destroy(&share->mutex);
my_free((gptr) share, MYF(0));
}
pthread_mutex_unlock(&example_mutex);
return 0;
}
static handler* example_create_handler(TABLE_SHARE *table, MEM_ROOT *mem_root)
{
return new (mem_root) ha_example(table);
}
ha_example::ha_example(TABLE_SHARE *table_arg)
:handler(&example_hton, table_arg)
{}
/*
If frm_error() is called then we will use this to to find out what file extentions
exist for the storage engine. This is also used by the default rename_table and
delete_table method in handler.cc.
*/
static const char *ha_example_exts[] = {
NullS
};
const char **ha_example::bas_ext() const
{
return ha_example_exts;
}
/*
Used for opening tables. The name will be the name of the file.
A table is opened when it needs to be opened. For instance
when a request comes in for a select on the table (tables are not
open and closed for each request, they are cached).
Called from handler.cc by handler::ha_open(). The server opens all tables by
calling ha_open() which then calls the handler specific open().
*/
int ha_example::open(const char *name, int mode, uint test_if_locked)
{
DBUG_ENTER("ha_example::open");
if (!(share = get_share(name, table)))
DBUG_RETURN(1);
thr_lock_data_init(&share->lock,&lock,NULL);
DBUG_RETURN(0);
}
/*
Closes a table. We call the free_share() function to free any resources
that we have allocated in the "shared" structure.
Called from sql_base.cc, sql_select.cc, and table.cc.
In sql_select.cc it is only used to close up temporary tables or during
the process where a temporary table is converted over to being a
myisam table.
For sql_base.cc look at close_data_tables().
*/
int ha_example::close(void)
{
DBUG_ENTER("ha_example::close");
DBUG_RETURN(free_share(share));
}
/*
write_row() inserts a row. No extra() hint is given currently if a bulk load
is happeneding. buf() is a byte array of data. You can use the field
information to extract the data from the native byte array type.
Example of this would be:
for (Field **field=table->field ; *field ; field++)
{
...
}
See ha_tina.cc for an example of extracting all of the data as strings.
ha_berekly.cc has an example of how to store it intact by "packing" it
for ha_berkeley's own native storage type.
See the note for update_row() on auto_increments and timestamps. This
case also applied to write_row().
Called from item_sum.cc, item_sum.cc, sql_acl.cc, sql_insert.cc,
sql_insert.cc, sql_select.cc, sql_table.cc, sql_udf.cc, and sql_update.cc.
*/
int ha_example::write_row(byte * buf)
{
DBUG_ENTER("ha_example::write_row");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
Yes, update_row() does what you expect, it updates a row. old_data will have
the previous row record in it, while new_data will have the newest data in
it.
Keep in mind that the server can do updates based on ordering if an ORDER BY
clause was used. Consecutive ordering is not guarenteed.
Currently new_data will not have an updated auto_increament record, or
and updated timestamp field. You can do these for example by doing these:
if (table->timestamp_field_type & TIMESTAMP_AUTO_SET_ON_UPDATE)
table->timestamp_field->set_time();
if (table->next_number_field && record == table->record[0])
update_auto_increment();
Called from sql_select.cc, sql_acl.cc, sql_update.cc, and sql_insert.cc.
*/
int ha_example::update_row(const byte * old_data, byte * new_data)
{
DBUG_ENTER("ha_example::update_row");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
This will delete a row. buf will contain a copy of the row to be deleted.
The server will call this right after the current row has been called (from
either a previous rnd_nexT() or index call).
If you keep a pointer to the last row or can access a primary key it will
make doing the deletion quite a bit easier.
Keep in mind that the server does no guarentee consecutive deletions. ORDER BY
clauses can be used.
Called in sql_acl.cc and sql_udf.cc to manage internal table information.
Called in sql_delete.cc, sql_insert.cc, and sql_select.cc. In sql_select it is
used for removing duplicates while in insert it is used for REPLACE calls.
*/
int ha_example::delete_row(const byte * buf)
{
DBUG_ENTER("ha_example::delete_row");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
Positions an index cursor to the index specified in the handle. Fetches the
row if available. If the key value is null, begin at the first key of the
index.
*/
int ha_example::index_read(byte * buf, const byte * key,
uint key_len __attribute__((unused)),
enum ha_rkey_function find_flag
__attribute__((unused)))
{
DBUG_ENTER("ha_example::index_read");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
Positions an index cursor to the index specified in key. Fetches the
row if any. This is only used to read whole keys.
*/
int ha_example::index_read_idx(byte * buf, uint index, const byte * key,
uint key_len __attribute__((unused)),
enum ha_rkey_function find_flag
__attribute__((unused)))
{
DBUG_ENTER("ha_example::index_read_idx");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
Used to read forward through the index.
*/
int ha_example::index_next(byte * buf)
{
DBUG_ENTER("ha_example::index_next");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
Used to read backwards through the index.
*/
int ha_example::index_prev(byte * buf)
{
DBUG_ENTER("ha_example::index_prev");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
index_first() asks for the first key in the index.
Called from opt_range.cc, opt_sum.cc, sql_handler.cc,
and sql_select.cc.
*/
int ha_example::index_first(byte * buf)
{
DBUG_ENTER("ha_example::index_first");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
index_last() asks for the last key in the index.
Called from opt_range.cc, opt_sum.cc, sql_handler.cc,
and sql_select.cc.
*/
int ha_example::index_last(byte * buf)
{
DBUG_ENTER("ha_example::index_last");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
rnd_init() is called when the system wants the storage engine to do a table
scan.
See the example in the introduction at the top of this file to see when
rnd_init() is called.
Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc,
and sql_update.cc.
*/
int ha_example::rnd_init(bool scan)
{
DBUG_ENTER("ha_example::rnd_init");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
int ha_example::rnd_end()
{
DBUG_ENTER("ha_example::rnd_end");
DBUG_RETURN(0);
}
/*
This is called for each row of the table scan. When you run out of records
you should return HA_ERR_END_OF_FILE. Fill buff up with the row information.
The Field structure for the table is the key to getting data into buf
in a manner that will allow the server to understand it.
Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc,
and sql_update.cc.
*/
int ha_example::rnd_next(byte *buf)
{
DBUG_ENTER("ha_example::rnd_next");
DBUG_RETURN(HA_ERR_END_OF_FILE);
}
/*
position() is called after each call to rnd_next() if the data needs
to be ordered. You can do something like the following to store
the position:
my_store_ptr(ref, ref_length, current_position);
The server uses ref to store data. ref_length in the above case is
the size needed to store current_position. ref is just a byte array
that the server will maintain. If you are using offsets to mark rows, then
current_position should be the offset. If it is a primary key like in
BDB, then it needs to be a primary key.
Called from filesort.cc, sql_select.cc, sql_delete.cc and sql_update.cc.
*/
void ha_example::position(const byte *record)
{
DBUG_ENTER("ha_example::position");
DBUG_VOID_RETURN;
}
/*
This is like rnd_next, but you are given a position to use
to determine the row. The position will be of the type that you stored in
ref. You can use ha_get_ptr(pos,ref_length) to retrieve whatever key
or position you saved when position() was called.
Called from filesort.cc records.cc sql_insert.cc sql_select.cc sql_update.cc.
*/
int ha_example::rnd_pos(byte * buf, byte *pos)
{
DBUG_ENTER("ha_example::rnd_pos");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
::info() is used to return information to the optimizer.
see my_base.h for the complete description
Currently this table handler doesn't implement most of the fields
really needed. SHOW also makes use of this data
Another note, you will probably want to have the following in your
code:
if (records < 2)
records = 2;
The reason is that the server will optimize for cases of only a single
record. If in a table scan you don't know the number of records
it will probably be better to set records to two so you can return
as many records as you need.
Along with records a few more variables you may wish to set are:
records
deleted
data_file_length
index_file_length
delete_length
check_time
Take a look at the public variables in handler.h for more information.
Called in:
filesort.cc
ha_heap.cc
item_sum.cc
opt_sum.cc
sql_delete.cc
sql_delete.cc
sql_derived.cc
sql_select.cc
sql_select.cc
sql_select.cc
sql_select.cc
sql_select.cc
sql_show.cc
sql_show.cc
sql_show.cc
sql_show.cc
sql_table.cc
sql_union.cc
sql_update.cc
*/
void ha_example::info(uint flag)
{
DBUG_ENTER("ha_example::info");
DBUG_VOID_RETURN;
}
/*
extra() is called whenever the server wishes to send a hint to
the storage engine. The myisam engine implements the most hints.
ha_innodb.cc has the most exhaustive list of these hints.
*/
int ha_example::extra(enum ha_extra_function operation)
{
DBUG_ENTER("ha_example::extra");
DBUG_RETURN(0);
}
/*
Deprecated and likely to be removed in the future. Storage engines normally
just make a call like:
ha_example::extra(HA_EXTRA_RESET);
to handle it.
*/
int ha_example::reset(void)
{
DBUG_ENTER("ha_example::reset");
DBUG_RETURN(0);
}
/*
Used to delete all rows in a table. Both for cases of truncate and
for cases where the optimizer realizes that all rows will be
removed as a result of a SQL statement.
Called from item_sum.cc by Item_func_group_concat::clear(),
Item_sum_count_distinct::clear(), and Item_func_group_concat::clear().
Called from sql_delete.cc by mysql_delete().
Called from sql_select.cc by JOIN::reinit().
Called from sql_union.cc by st_select_lex_unit::exec().
*/
int ha_example::delete_all_rows()
{
DBUG_ENTER("ha_example::delete_all_rows");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
First you should go read the section "locking functions for mysql" in
lock.cc to understand this.
This create a lock on the table. If you are implementing a storage engine
that can handle transacations look at ha_berkely.cc to see how you will
want to goo about doing this. Otherwise you should consider calling flock()
here.
Called from lock.cc by lock_external() and unlock_external(). Also called
from sql_table.cc by copy_data_between_tables().
*/
int ha_example::external_lock(THD *thd, int lock_type)
{
DBUG_ENTER("ha_example::external_lock");
DBUG_RETURN(0);
}
/*
The idea with handler::store_lock() is the following:
The statement decided which locks we should need for the table
for updates/deletes/inserts we get WRITE locks, for SELECT... we get
read locks.
Before adding the lock into the table lock handler (see thr_lock.c)
mysqld calls store lock with the requested locks. Store lock can now
modify a write lock to a read lock (or some other lock), ignore the
lock (if we don't want to use MySQL table locks at all) or add locks
for many tables (like we do when we are using a MERGE handler).
Berkeley DB for example changes all WRITE locks to TL_WRITE_ALLOW_WRITE
(which signals that we are doing WRITES, but we are still allowing other
reader's and writer's.
When releasing locks, store_lock() are also called. In this case one
usually doesn't have to do anything.
In some exceptional cases MySQL may send a request for a TL_IGNORE;
This means that we are requesting the same lock as last time and this
should also be ignored. (This may happen when someone does a flush
table when we have opened a part of the tables, in which case mysqld
closes and reopens the tables and tries to get the same locks at last
time). In the future we will probably try to remove this.
Called from lock.cc by get_lock_data().
*/
THR_LOCK_DATA **ha_example::store_lock(THD *thd,
THR_LOCK_DATA **to,
enum thr_lock_type lock_type)
{
if (lock_type != TL_IGNORE && lock.type == TL_UNLOCK)
lock.type=lock_type;
*to++= &lock;
return to;
}
/*
Used to delete a table. By the time delete_table() has been called all
opened references to this table will have been closed (and your globally
shared references released. The variable name will just be the name of
the table. You will need to remove any files you have created at this point.
If you do not implement this, the default delete_table() is called from
handler.cc and it will delete all files with the file extentions returned
by bas_ext().
Called from handler.cc by delete_table and ha_create_table(). Only used
during create if the table_flag HA_DROP_BEFORE_CREATE was specified for
the storage engine.
*/
int ha_example::delete_table(const char *name)
{
DBUG_ENTER("ha_example::delete_table");
/* This is not implemented but we want someone to be able that it works. */
DBUG_RETURN(0);
}
/*
Renames a table from one name to another from alter table call.
If you do not implement this, the default rename_table() is called from
handler.cc and it will delete all files with the file extentions returned
by bas_ext().
Called from sql_table.cc by mysql_rename_table().
*/
int ha_example::rename_table(const char * from, const char * to)
{
DBUG_ENTER("ha_example::rename_table ");
DBUG_RETURN(HA_ERR_WRONG_COMMAND);
}
/*
Given a starting key, and an ending key estimate the number of rows that
will exist between the two. end_key may be empty which in case determine
if start_key matches any rows.
Called from opt_range.cc by check_quick_keys().
*/
ha_rows ha_example::records_in_range(uint inx, key_range *min_key,
key_range *max_key)
{
DBUG_ENTER("ha_example::records_in_range");
DBUG_RETURN(10); // low number to force index usage
}
/*
create() is called to create a database. The variable name will have the name
of the table. When create() is called you do not need to worry about opening
the table. Also, the FRM file will have already been created so adjusting
create_info will not do you any good. You can overwrite the frm file at this
point if you wish to change the table definition, but there are no methods
currently provided for doing that.
Called from handle.cc by ha_create_table().
*/
int ha_example::create(const char *name, TABLE *table_arg,
HA_CREATE_INFO *create_info)
{
DBUG_ENTER("ha_example::create");
/* This is not implemented but we want someone to be able that it works. */
DBUG_RETURN(0);
}
mysql_declare_plugin(example)
{
MYSQL_STORAGE_ENGINE_PLUGIN,
&example_hton,
example_hton_name,
"Brian Aker, MySQL AB",
example_hton_comment,
example_init_func, /* Plugin Init */
example_done_func, /* Plugin Deinit */
0x0001 /* 0.1 */,
0
}
mysql_declare_plugin_end;
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