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| -rw-r--r-- | sql/handler.h | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/sql/handler.h b/sql/handler.h index a4bedc2f075..c53fe86504b 100644 --- a/sql/handler.h +++ b/sql/handler.h @@ -249,14 +249,66 @@ typedef struct xid_t XID; #define MIN_XID_LIST_SIZE 128 #define MAX_XID_LIST_SIZE (1024*128) +/* + handlerton is a singleton structure - one instance per storage engine - + to provide access to storage engine functionality that works on + "global" level (unlike handler class that works on per-table basis) + + usually handlerton instance is defined statically in ha_xxx.cc as + + static handlerton { ... } xxx_hton; + + savepoint_*, prepare, recover, and *_by_xid pointers can be 0. +*/ typedef struct { + /* + each storage engine has it's own memory area (actually a pointer) + in the thd, for storing per-connection information. + It is accessed as + + thd->ha_data[xxx_hton.slot] + + slot number is initialized by MySQL after xxx_init() is called. + */ uint slot; + /* + to store per-savepoint data storage engine is provided with an area + of a requested size (0 is ok here). + savepoint_offset must be initialized statically to the size of + the needed memory to store per-savepoint information. + After xxx_init it is changed to be an offset to savepoint storage + area and need not be used by storage engine. + see binlog_hton and binlog_savepoint_set/rollback for an example. + */ uint savepoint_offset; + /* + handlerton methods: + + close_connection is only called if + thd->ha_data[xxx_hton.slot] is non-zero, so even if you don't need + this storage area - set it to something, so that MySQL would know + this storage engine was accessed in this connection + */ int (*close_connection)(THD *thd); + /* + sv points to an uninitialized storage area of requested size + (see savepoint_offset description) + */ int (*savepoint_set)(THD *thd, void *sv); + /* + sv points to a storage area, that was earlier passed + to the savepoint_set call + */ int (*savepoint_rollback)(THD *thd, void *sv); int (*savepoint_release)(THD *thd, void *sv); + /* + 'all' is true if it's a real commit, that makes persistent changes + 'all' is false if it's not in fact a commit but an end of the + statement that is part of the transaction. + NOTE 'all' is also false in auto-commit mode where 'end of statement' + and 'real commit' mean the same event. + */ int (*commit)(THD *thd, bool all); int (*rollback)(THD *thd, bool all); int (*prepare)(THD *thd, bool all); |