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Updated file to use doxygen commenting style.

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trudy@linux.site 2006-12-18 18:08:38 -08:00
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storage/example/ha_example.cc
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@ -14,31 +14,45 @@
along with this program; if not, write to the Free Software along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/* /** @file ha_example.cc
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 @brief
in your buld by doing the following during your build process: The ha_example engine is a stubbed storage engine for example purposes only;
it does nothing at this point. Its purpose is to provide a source
code illustration of how to begin writing new storage engines; see also
/storage/example/ha_example.h.
@details
ha_example will let you create/open/delete tables, but nothing further
(for example, indexes are not supported nor can data be stored in the
table). Use this example as a template for implementing the same functionality
in your own storage engine. You can enable the example storage engine in
your build by doing the following during your build process:<br>
./configure --with-example-storage-engine ./configure --with-example-storage-engine
Once this is done mysql will let you create tables with: Once this is done, MySQL will let you create tables with:<br>
CREATE TABLE A (...) ENGINE=EXAMPLE; CREATE TABLE <table name> (...) ENGINE=EXAMPLE;
The example is setup to use table locks. It implements an example "SHARE" The example storage engine is set up to use table locks. It implements an
that is inserted into a hash by table name. You can use this to store example "SHARE" that is inserted into a hash by table name. You can use this
information of state that any example handler object will be able to see to store information of state that any example handler object will be able to
if it is using the same table. see when it is using that table.
Please read the object definition in ha_example.h before reading the rest Please read the object definition in ha_example.h before reading the rest
if this file. of this file.
To get an idea of what occurs here is an example select that would do a @note
scan of an entire table: When you create an EXAMPLE table, the MySQL Server creates a table .frm (format)
file in the database directory, using the table name as the file name as is
customary with MySQL. No other files are created. To get an idea of what occurs,
here is an example select that would do a scan of an entire table:
@code
ha_example::store_lock ha_example::store_lock
ha_example::external_lock ha_example::external_lock
ha_example::info ha_example::info
ha_example::rnd_init ha_example::rnd_init
ha_example::extra ha_example::extra
ENUM HA_EXTRA_CACHE Cash record in HA_rrnd() ENUM HA_EXTRA_CACHE Cache 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
@ -49,19 +63,20 @@
ha_example::rnd_next ha_example::rnd_next
ha_example::rnd_next ha_example::rnd_next
ha_example::extra ha_example::extra
ENUM HA_EXTRA_NO_CACHE End cacheing of records (def) ENUM HA_EXTRA_NO_CACHE End caching of records (def)
ha_example::external_lock ha_example::external_lock
ha_example::extra ha_example::extra
ENUM HA_EXTRA_RESET Reset database to after open ENUM HA_EXTRA_RESET Reset database to after open
@endcode
In the above example has 9 row called before rnd_next signalled that it was Here you see that the example storage engine has 9 rows called before rnd_next
at the end of its data. In the above example the table was already opened signals that it has reached the end of its data. Also note that the table in
(or you would have seen a call to ha_example::open(). Calls to question was already opened; had it not been open, a call to ha_example::open()
ha_example::extra() are hints as to what will be occuring to the request. would also have been necessary. Calls to ha_example::extra() are hints as to
what will be occuring to the request.
Happy coding! Happy coding!<br>
-Brian -Brian
*/ */
#ifdef USE_PRAGMA_IMPLEMENTATION #ifdef USE_PRAGMA_IMPLEMENTATION
@ -71,7 +86,6 @@
#define MYSQL_SERVER 1 #define MYSQL_SERVER 1
#include "mysql_priv.h" #include "mysql_priv.h"
#include "ha_example.h" #include "ha_example.h"
#include <mysql/plugin.h> #include <mysql/plugin.h>
static handler *example_create_handler(handlerton *hton, static handler *example_create_handler(handlerton *hton,
@ -82,12 +96,11 @@ static int example_init_func();
handlerton *example_hton; handlerton *example_hton;
/* Variables for example share methods */ /* Variables for example share methods */
static HASH example_open_tables; // Hash used to track open tables static HASH example_open_tables; ///< Hash used to track the number of open tables; variable for example share methods
pthread_mutex_t example_mutex; // This is the mutex we use to init the hash pthread_mutex_t example_mutex; ///< This is the mutex used to init the hash; variable for example share methods
static int example_init= 0; // Variable for checking the init state of hash static int example_init= 0; ///< This variable is used to check the init state of hash; variable for example share methods
/** @brief
/*
Function we use in the creation of our hash to get key. Function we use in the creation of our hash to get key.
*/ */
static byte* example_get_key(EXAMPLE_SHARE *share,uint *length, static byte* example_get_key(EXAMPLE_SHARE *share,uint *length,
@ -127,8 +140,8 @@ static int example_done_func(void *p)
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/* /** @brief
Example of simple lock controls. The "share" it creates is structure we will Example of simple lock controls. The "share" it creates is a structure we will
pass to each example handler. Do you have to have one of these? Well, you have 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. pieces that are used for locking, and they are needed to function.
*/ */
@ -176,10 +189,9 @@ error:
return NULL; return NULL;
} }
/** @brief
/*
Free lock controls. We call this whenever we close a table. If the table had 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. the last reference to the share, then we free memory associated with it.
*/ */
static int free_share(EXAMPLE_SHARE *share) static int free_share(EXAMPLE_SHARE *share)
{ {
@ -196,7 +208,6 @@ static int free_share(EXAMPLE_SHARE *share)
return 0; return 0;
} }
static handler* example_create_handler(handlerton *hton, static handler* example_create_handler(handlerton *hton,
TABLE_SHARE *table, TABLE_SHARE *table,
MEM_ROOT *mem_root) MEM_ROOT *mem_root)
@ -204,15 +215,18 @@ static handler* example_create_handler(handlerton *hton,
return new (mem_root) ha_example(hton, table); return new (mem_root) ha_example(hton, table);
} }
ha_example::ha_example(handlerton *hton, TABLE_SHARE *table_arg) ha_example::ha_example(handlerton *hton, TABLE_SHARE *table_arg)
:handler(hton, table_arg) :handler(hton, table_arg)
{} {}
/* /** @brief
If frm_error() is called then we will use this to to find out what file extentions If frm_error() is called then we will use this to determine the file extensions
exist for the storage engine. This is also used by the default rename_table and that exist for the storage engine. This is also used by the default rename_table
delete_table method in handler.cc. and delete_table method in handler.cc.
@see
rename_table method in handler.cc and
delete_table method in handler.cc
*/ */
static const char *ha_example_exts[] = { static const char *ha_example_exts[] = {
NullS NullS
@ -223,15 +237,19 @@ const char **ha_example::bas_ext() const
return ha_example_exts; return ha_example_exts;
} }
/** @brief
/*
Used for opening tables. The name will be the name of the file. 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 @details
open and closed for each request, they are cached). A table is opened when it needs to be opened; e.g. 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 Called from handler.cc by handler::ha_open(). The server opens all tables by
calling ha_open() which then calls the handler specific open(). calling ha_open() which then calls the handler specific open().
@see
handler::ha_open() in handler.cc
*/ */
int ha_example::open(const char *name, int mode, uint test_if_locked) int ha_example::open(const char *name, int mode, uint test_if_locked)
{ {
@ -244,16 +262,19 @@ int ha_example::open(const char *name, int mode, uint test_if_locked)
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/** @brief
/*
Closes a table. We call the free_share() function to free any resources Closes a table. We call the free_share() function to free any resources
that we have allocated in the "shared" structure. that we have allocated in the "shared" structure.
Called from sql_base.cc, sql_select.cc, and table.cc. @details
In sql_select.cc it is only used to close up temporary tables or during Called from sql_base.cc, sql_select.cc, and table.cc. In sql_select.cc it is
the process where a temporary table is converted over to being a only used to close up temporary tables or during the process where a temporary
myisam table. table is converted over to being a myisam table.
For sql_base.cc look at close_data_tables(). For sql_base.cc look at close_data_tables().
@see
sql_base.cc, sql_select.cc and table.cc
*/ */
int ha_example::close(void) int ha_example::close(void)
{ {
@ -261,26 +282,33 @@ int ha_example::close(void)
DBUG_RETURN(free_share(share)); DBUG_RETURN(free_share(share));
} }
/** @brief
/*
write_row() inserts a row. No extra() hint is given currently if a bulk load 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 is happening. buf() is a byte array of data. You can use the field
information to extract the data from the native byte array type. information to extract the data from the native byte array type.
@details
Example of this would be: Example of this would be:
@code
for (Field **field=table->field ; *field ; field++) for (Field **field=table->field ; *field ; field++)
{ {
... ...
} }
@endcode
See ha_tina.cc for an example of extracting all of the data as strings. 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 ha_berekly.cc has an example of how to store it intact by "packing" it
for ha_berkeley's own native storage type. for ha_berkeley's own native storage type.
See the note for update_row() on auto_increments and timestamps. This See the note for update_row() on auto_increments and timestamps. This
case also applied to write_row(). case also applies to write_row().
Called from item_sum.cc, item_sum.cc, sql_acl.cc, sql_insert.cc, 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. sql_insert.cc, sql_select.cc, sql_table.cc, sql_udf.cc, and sql_update.cc.
@see
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) int ha_example::write_row(byte * buf)
{ {
@ -288,21 +316,26 @@ int ha_example::write_row(byte * buf)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
Yes, update_row() does what you expect, it updates a row. old_data will have 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 the previous row record in it, while new_data will have the newest data in it.
it.
Keep in mind that the server can do updates based on ordering if an ORDER BY Keep in mind that the server can do updates based on ordering if an ORDER BY
clause was used. Consecutive ordering is not guarenteed. clause was used. Consecutive ordering is not guaranteed.
@details
Currently new_data will not have an updated auto_increament record, or 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: and updated timestamp field. You can do these for example by doing:
@code
if (table->timestamp_field_type & TIMESTAMP_AUTO_SET_ON_UPDATE) if (table->timestamp_field_type & TIMESTAMP_AUTO_SET_ON_UPDATE)
table->timestamp_field->set_time(); table->timestamp_field->set_time();
if (table->next_number_field && record == table->record[0]) if (table->next_number_field && record == table->record[0])
update_auto_increment(); update_auto_increment();
@endcode
Called from sql_select.cc, sql_acl.cc, sql_update.cc, and sql_insert.cc. Called from sql_select.cc, sql_acl.cc, sql_update.cc, and sql_insert.cc.
@see
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) int ha_example::update_row(const byte * old_data, byte * new_data)
{ {
@ -311,19 +344,22 @@ int ha_example::update_row(const byte * old_data, byte * new_data)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
This will delete a row. buf will contain a copy of the row to be deleted. 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 The server will call this right after the current row has been called (from
either a previous rnd_nexT() or index call). either a previous rnd_nexT() or index call).
@details
If you keep a pointer to the last row or can access a primary key it will 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. make doing the deletion quite a bit easier. Keep in mind that the server does
Keep in mind that the server does no guarentee consecutive deletions. ORDER BY not guarantee consecutive deletions. ORDER BY clauses can be used.
clauses can be used.
Called in sql_acl.cc and sql_udf.cc to manage internal table information. 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 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. used for removing duplicates while in insert it is used for REPLACE calls.
@see
sql_acl.cc, sql_udf.cc, sql_delete.cc, sql_insert.cc and sql_select.cc
*/ */
int ha_example::delete_row(const byte * buf) int ha_example::delete_row(const byte * buf)
{ {
@ -331,8 +367,7 @@ int ha_example::delete_row(const byte * buf)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
Positions an index cursor to the index specified in the handle. Fetches the 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 row if available. If the key value is null, begin at the first key of the
index. index.
@ -346,8 +381,7 @@ int ha_example::index_read(byte * buf, const byte * key,
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
Used to read forward through the index. Used to read forward through the index.
*/ */
int ha_example::index_next(byte * buf) int ha_example::index_next(byte * buf)
@ -356,8 +390,7 @@ int ha_example::index_next(byte * buf)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
Used to read backwards through the index. Used to read backwards through the index.
*/ */
int ha_example::index_prev(byte * buf) int ha_example::index_prev(byte * buf)
@ -366,12 +399,14 @@ int ha_example::index_prev(byte * buf)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
index_first() asks for the first key in the index. index_first() asks for the first key in the index.
Called from opt_range.cc, opt_sum.cc, sql_handler.cc, @details
and sql_select.cc. Called from opt_range.cc, opt_sum.cc, sql_handler.cc, and sql_select.cc.
@see
opt_range.cc, opt_sum.cc, sql_handler.cc and sql_select.cc
*/ */
int ha_example::index_first(byte * buf) int ha_example::index_first(byte * buf)
{ {
@ -379,12 +414,14 @@ int ha_example::index_first(byte * buf)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
index_last() asks for the last key in the index. index_last() asks for the last key in the index.
Called from opt_range.cc, opt_sum.cc, sql_handler.cc, @details
and sql_select.cc. Called from opt_range.cc, opt_sum.cc, sql_handler.cc, and sql_select.cc.
@see
opt_range.cc, opt_sum.cc, sql_handler.cc and sql_select.cc
*/ */
int ha_example::index_last(byte * buf) int ha_example::index_last(byte * buf)
{ {
@ -392,15 +429,17 @@ int ha_example::index_last(byte * buf)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
rnd_init() is called when the system wants the storage engine to do a table rnd_init() is called when the system wants the storage engine to do a table
scan. scan. See the example in the introduction at the top of this file to see when
See the example in the introduction at the top of this file to see when
rnd_init() is called. rnd_init() is called.
@details
Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc, Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc,
and sql_update.cc. and sql_update.cc.
@see
filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc and sql_update.cc
*/ */
int ha_example::rnd_init(bool scan) int ha_example::rnd_init(bool scan)
{ {
@ -414,14 +453,18 @@ int ha_example::rnd_end()
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/* /** @brief
This is called for each row of the table scan. When you run out of records 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. 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 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. in a manner that will allow the server to understand it.
@details
Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc, Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc,
and sql_update.cc. and sql_update.cc.
@see
filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc and sql_update.cc
*/ */
int ha_example::rnd_next(byte *buf) int ha_example::rnd_next(byte *buf)
{ {
@ -429,20 +472,25 @@ int ha_example::rnd_next(byte *buf)
DBUG_RETURN(HA_ERR_END_OF_FILE); DBUG_RETURN(HA_ERR_END_OF_FILE);
} }
/** @brief
/*
position() is called after each call to rnd_next() if the data needs 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 to be ordered. You can do something like the following to store
the position: the position:
@code
my_store_ptr(ref, ref_length, current_position); my_store_ptr(ref, ref_length, current_position);
@endcode
@details
The server uses ref to store data. ref_length in the above case is 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 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 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 current_position should be the offset. If it is a primary key like in
BDB, then it needs to be a primary key. BDB, then it needs to be a primary key.
Called from filesort.cc, sql_select.cc, sql_delete.cc and sql_update.cc. Called from filesort.cc, sql_select.cc, sql_delete.cc, and sql_update.cc.
@see
filesort.cc, sql_select.cc, sql_delete.cc and sql_update.cc
*/ */
void ha_example::position(const byte *record) void ha_example::position(const byte *record)
{ {
@ -450,13 +498,17 @@ void ha_example::position(const byte *record)
DBUG_VOID_RETURN; DBUG_VOID_RETURN;
} }
/** @brief
/*
This is like rnd_next, but you are given a position to use 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 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 ref. You can use ha_get_ptr(pos,ref_length) to retrieve whatever key
or position you saved when position() was called. or position you saved when position() was called.
Called from filesort.cc records.cc sql_insert.cc sql_select.cc sql_update.cc.
@details
Called from filesort.cc, records.cc, sql_insert.cc, sql_select.cc, and sql_update.cc.
@see
filesort.cc, records.cc, sql_insert.cc, sql_select.cc and sql_update.cc
*/ */
int ha_example::rnd_pos(byte * buf, byte *pos) int ha_example::rnd_pos(byte * buf, byte *pos)
{ {
@ -464,22 +516,24 @@ int ha_example::rnd_pos(byte * buf, byte *pos)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
::info() is used to return information to the optimizer. See my_base.h for
the complete description.
/* @details
::info() is used to return information to the optimizer. Currently this table handler doesn't implement most of the fields really needed.
see my_base.h for the complete description SHOW also makes use of this data.
Currently this table handler doesn't implement most of the fields You will probably want to have the following in your code:
really needed. SHOW also makes use of this data @code
Another note, you will probably want to have the following in your
code:
if (records < 2) if (records < 2)
records = 2; records = 2;
@endcode
The reason is that the server will optimize for cases of only a single 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 record. If, in a table scan, you don't know the number of records, it
it will probably be better to set records to two so you can return will probably be better to set records to two so you can return as many
as many records as you need. records as you need. Along with records, a few more variables you may wish
Along with records a few more variables you may wish to set are: to set are:
records records
deleted deleted
data_file_length data_file_length
@ -488,27 +542,16 @@ int ha_example::rnd_pos(byte * buf, byte *pos)
check_time check_time
Take a look at the public variables in handler.h for more information. Take a look at the public variables in handler.h for more information.
Called in: Called in filesort.cc, ha_heap.cc, item_sum.cc, opt_sum.cc, sql_delete.cc,
filesort.cc sql_delete.cc, sql_derived.cc, sql_select.cc, sql_select.cc, sql_select.cc,
ha_heap.cc sql_select.cc, sql_select.cc, sql_show.cc, sql_show.cc, sql_show.cc, sql_show.cc,
item_sum.cc sql_table.cc, sql_union.cc, and sql_update.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
@see
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 and sql_update.cc
*/ */
int ha_example::info(uint flag) int ha_example::info(uint flag)
{ {
@ -516,11 +559,13 @@ int ha_example::info(uint flag)
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/** @brief
/*
extra() is called whenever the server wishes to send a hint to extra() is called whenever the server wishes to send a hint to
the storage engine. The myisam engine implements the most hints. the storage engine. The myisam engine implements the most hints.
ha_innodb.cc has the most exhaustive list of these hints. ha_innodb.cc has the most exhaustive list of these hints.
@see
ha_innodb.cc
*/ */
int ha_example::extra(enum ha_extra_function operation) int ha_example::extra(enum ha_extra_function operation)
{ {
@ -528,17 +573,23 @@ int ha_example::extra(enum ha_extra_function operation)
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/** @brief
Used to delete all rows in a table, including cases of truncate and cases where
the optimizer realizes that all rows will be removed as a result of an SQL statement.
/* @details
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(), Called from item_sum.cc by Item_func_group_concat::clear(),
Item_sum_count_distinct::clear(), and 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_delete.cc by mysql_delete().
Called from sql_select.cc by JOIN::reinit(). Called from sql_select.cc by JOIN::reinit().
Called from sql_union.cc by st_select_lex_unit::exec(). Called from sql_union.cc by st_select_lex_unit::exec().
@see
Item_func_group_concat::clear(), Item_sum_count_distinct::clear() and
Item_func_group_concat::clear() in item_sum.cc;
mysql_delete() in sql_delete.cc;
JOIN::reinit() in sql_select.cc and
st_select_lex_unit::exec() in sql_union.cc.
*/ */
int ha_example::delete_all_rows() int ha_example::delete_all_rows()
{ {
@ -546,17 +597,21 @@ int ha_example::delete_all_rows()
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/** @brief
/*
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 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 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() want to go about doing this. Otherwise you should consider calling flock()
here. here. Hint: Read the section "locking functions for mysql" in lock.cc to understand
this.
@details
Called from lock.cc by lock_external() and unlock_external(). Also called Called from lock.cc by lock_external() and unlock_external(). Also called
from sql_table.cc by copy_data_between_tables(). from sql_table.cc by copy_data_between_tables().
@see
lock.cc by lock_external() and unlock_external() in lock.cc;
the section "locking functions for mysql" in lock.cc;
copy_data_between_tables() in sql_table.cc.
*/ */
int ha_example::external_lock(THD *thd, int lock_type) int ha_example::external_lock(THD *thd, int lock_type)
{ {
@ -564,25 +619,23 @@ int ha_example::external_lock(THD *thd, int lock_type)
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/** @brief
The idea with handler::store_lock() is: The statement decides which locks
should be needed for the table. For updates/deletes/inserts we get WRITE
locks, for SELECT... we get read locks.
/* @details
The idea with handler::store_lock() is the following: 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
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 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 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). 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 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 (which signals that we are doing WRITES, but are still allowing other
reader's and writer's. readers and writers).
When releasing locks, store_lock() are also called. In this case one When releasing locks, store_lock() is also called. In this case one
usually doesn't have to do anything. usually doesn't have to do anything.
In some exceptional cases MySQL may send a request for a TL_IGNORE; In some exceptional cases MySQL may send a request for a TL_IGNORE;
@ -590,9 +643,12 @@ int ha_example::external_lock(THD *thd, int lock_type)
should also be ignored. (This may happen when someone does a flush 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 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 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. time). In the future we will probably try to remove this.
Called from lock.cc by get_lock_data(). Called from lock.cc by get_lock_data().
@see
get_lock_data() in lock.cc
*/ */
THR_LOCK_DATA **ha_example::store_lock(THD *thd, THR_LOCK_DATA **ha_example::store_lock(THD *thd,
THR_LOCK_DATA **to, THR_LOCK_DATA **to,
@ -604,19 +660,23 @@ THR_LOCK_DATA **ha_example::store_lock(THD *thd,
return to; return to;
} }
/* /** @brief
Used to delete a table. By the time delete_table() has been called all 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 opened references to this table will have been closed (and your globally
shared references released. The variable name will just be the name of 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. the table. You will need to remove any files you have created at this point.
@details
If you do not implement this, the default delete_table() is called from 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 handler.cc and it will delete all files with the file extensions returned
by bas_ext(). by bas_ext().
Called from handler.cc by delete_table and ha_create_table(). Only used 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 during create if the table_flag HA_DROP_BEFORE_CREATE was specified for
the storage engine. the storage engine.
@see
delete_table and ha_create_table() in handler.cc
*/ */
int ha_example::delete_table(const char *name) int ha_example::delete_table(const char *name)
{ {
@ -625,14 +685,18 @@ int ha_example::delete_table(const char *name)
DBUG_RETURN(0); DBUG_RETURN(0);
} }
/* /** @brief
Renames a table from one name to another from alter table call. Renames a table from one name to another via an alter table call.
@details
If you do not implement this, the default rename_table() is called from 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 handler.cc and it will delete all files with the file extensions returned
by bas_ext(). by bas_ext().
Called from sql_table.cc by mysql_rename_table(). Called from sql_table.cc by mysql_rename_table().
@see
mysql_rename_table() in sql_table.cc
*/ */
int ha_example::rename_table(const char * from, const char * to) int ha_example::rename_table(const char * from, const char * to)
{ {
@ -640,12 +704,17 @@ int ha_example::rename_table(const char * from, const char * to)
DBUG_RETURN(HA_ERR_WRONG_COMMAND); DBUG_RETURN(HA_ERR_WRONG_COMMAND);
} }
/* /** @brief
Given a starting key, and an ending key estimate the number of rows that 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 will exist between the two keys.
if start_key matches any rows.
@details
end_key may be empty, in which case determine if start_key matches any rows.
Called from opt_range.cc by check_quick_keys(). Called from opt_range.cc by check_quick_keys().
@see
check_quick_keys() in opt_range.cc
*/ */
ha_rows ha_example::records_in_range(uint inx, key_range *min_key, ha_rows ha_example::records_in_range(uint inx, key_range *min_key,
key_range *max_key) key_range *max_key)
@ -654,16 +723,20 @@ ha_rows ha_example::records_in_range(uint inx, key_range *min_key,
DBUG_RETURN(10); // low number to force index usage DBUG_RETURN(10); // low number to force index usage
} }
/** @brief
/*
create() is called to create a database. The variable name will have the name 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 of the table.
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 @details
point if you wish to change the table definition, but there are no methods When create() is called you do not need to worry about opening the table. Also,
currently provided for doing that. the .frm file will have already been created so adjusting create_info is not
necessary. 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 so.
Called from handle.cc by ha_create_table(). Called from handle.cc by ha_create_table().
@see
ha_create_table() in handle.cc
*/ */
int ha_example::create(const char *name, TABLE *table_arg, int ha_example::create(const char *name, TABLE *table_arg,
HA_CREATE_INFO *create_info) HA_CREATE_INFO *create_info)
@ -676,7 +749,6 @@ int ha_example::create(const char *name, TABLE *table_arg,
struct st_mysql_storage_engine example_storage_engine= struct st_mysql_storage_engine example_storage_engine=
{ MYSQL_HANDLERTON_INTERFACE_VERSION }; { MYSQL_HANDLERTON_INTERFACE_VERSION };
mysql_declare_plugin(example) mysql_declare_plugin(example)
{ {
MYSQL_STORAGE_ENGINE_PLUGIN, MYSQL_STORAGE_ENGINE_PLUGIN,
@ -693,4 +765,3 @@ mysql_declare_plugin(example)
NULL /* config options */ NULL /* config options */
} }
mysql_declare_plugin_end; mysql_declare_plugin_end;