20.5.1 Event Class Archaeological Notes

Despite the "V3" in the type code name, START_EVENT_V3 currently is used as the type code not only for v3 start events, but also for v1 start events. The original symbol for type code 1 was START_EVENT in the format now known as v1. Later, when v3 was developed, type code 1 was reused and the symbol associated with it was renamed from START_EVENT to START_EVENT_V3. The start events for both v1 and v3 therefore have a type code of 1, although the event structures differ and must be distinguished by examining their contents.

Up to MySQL 5.1.17, event type codes from 20 to 22 were associated with symbols and classes as follows:

Value	Type Code	Class
20	WRITE_ROWS_EVENT	Write_rows_log_event
21	UPDATE_ROWS_EVENT	Update_rows_log_event
22	DELETE_ROWS_EVENT	Delete_rows_log_event

In 5.1.18, the symbols and classes were renamed:

Value	Type Code	Class
20	PRE_GA_WRITE_ROWS_EVENT	Write_rows_log_event_old
21	PRE_GA_UPDATE_ROWS_EVENT	Update_rows_log_event_old
22	PRE_GA_DELETE_ROWS_EVENT	Delete_rows_log_event_old

Also in 5.1.18, the original symbols were reused with different values and new implementations of the classes that used the original names:

Value	Type Code	Class
23	WRITE_ROWS_EVENT	Write_rows_log_event
24	UPDATE_ROWS_EVENT	Update_rows_log_event
25	DELETE_ROWS_EVENT	Delete_rows_log_event

Events with type codes 20 to 22 are obsolete now and appear only in binary logs created by servers from MySQL 5.1.5 to 5.1.17.