Toru Maesaka

Yesterday I merged the BlitzDB tree with Drizzle‘s trunk for the first time in a long time (yeah…) and discovered some interesting changes made to the storage subsystem while I was away.

Previously all functions that caused an action to the storage engine was a member of the handler class but various things like table creation and transaction related functions have now moved to the StorageEngine class. These changes are somewhat drastic but makes good sense for Drizzle to grow further since it makes the subsystem easier to understand and frees Drizzle from the interface design that was strongly affected by MyISAM. For those that are interested, the StorageEngine class is located in “drizzled/plugin/storage_engine.h”.

For me it was pretty easy to update BlitzDB to work with the new subsystem since I don’t have anything special in the engine that required me to use my brain. I only had to move bas_ext(), table creation and rename functions over to the StorageEngine class and adjust it to the new interface:

int createTableImpl(Session *session, const char *table_name, 
                    Table *table_arg, HA_CREATE_INFO *ha_create_info); 
 
int renameTableImpl(Session *session, const char *from, const char *to);

For a real example, I recommend comparing the old InnobaseEngine class declaration with the updated one. As for where this redesign is going, this is the answer I got on the Drizzle channel from Stewart who did the actual work for all this.

stewart: tmaesaka: the basic idea is that handler becomes a cursor. the StorageEngine is for actions on the engine.
stewart: tmaesaka: and handler is a cursor on a table.

Something to keep in mind if you’re thinking about creating or porting a storage engine to Drizzle :)

Toru Maesaka drizzle, oss drizzle, mysql, storage