20.5 Event Classes and Types

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20.5.1 Event Class Archaeological Notes

Internally, the server uses C++ classes to represent binary log events. Prototypes are in log_event.h. Code for methods of these classes is in log_event.cc.

Log_event is the base class. Other more specific event subclasses are derived from it. Type codes are associated with subclasses because class instance contents are written to binary or relay logs or are sent over the network from master to slave. In those contexts, an event is just a sequence of bytes, not a class structure, so a type code is needed to allow recognition of the event type from the byte sequence.

An event byte sequence has a header part and a data part. The type code appears in the header part of each event.

The possible type codes for events are listed in the Log_event_type enumeration:

enum Log_event_type { 
  UNKNOWN_EVENT= 0, 
  START_EVENT_V3= 1, 
  QUERY_EVENT= 2, 
  STOP_EVENT= 3, 
  ROTATE_EVENT= 4, 
  INTVAR_EVENT= 5, 
  LOAD_EVENT= 6, 
  SLAVE_EVENT= 7, 
  CREATE_FILE_EVENT= 8, 
  APPEND_BLOCK_EVENT= 9, 
  EXEC_LOAD_EVENT= 10, 
  DELETE_FILE_EVENT= 11, 
  NEW_LOAD_EVENT= 12, 
  RAND_EVENT= 13, 
  USER_VAR_EVENT= 14, 
  FORMAT_DESCRIPTION_EVENT= 15, 
  XID_EVENT= 16, 
  BEGIN_LOAD_QUERY_EVENT= 17, 
  EXECUTE_LOAD_QUERY_EVENT= 18, 
  TABLE_MAP_EVENT = 19, 
  PRE_GA_WRITE_ROWS_EVENT = 20, 
  PRE_GA_UPDATE_ROWS_EVENT = 21, 
  PRE_GA_DELETE_ROWS_EVENT = 22, 
  WRITE_ROWS_EVENT = 23, 
  UPDATE_ROWS_EVENT = 24, 
  DELETE_ROWS_EVENT = 25, 
  INCIDENT_EVENT= 26, 
  HEARTBEAT_LOG_EVENT= 27, 
  IGNORABLE_LOG_EVENT= 28,
  ROWS_QUERY_LOG_EVENT= 29,
  WRITE_ROWS_EVENT = 30,
  UPDATE_ROWS_EVENT = 31,
  DELETE_ROWS_EVENT = 32,
  GTID_LOG_EVENT= 33,
  ANONYMOUS_GTID_LOG_EVENT= 34,
  PREVIOUS_GTIDS_LOG_EVENT= 35, 
  ENUM_END_EVENT 
  /* end marker */ 
};

The INTVAR_EVENT type has "subtypes," listed in the Int_event_type enumeration:

enum Int_event_type { 
  INVALID_INT_EVENT = LAST_INSERT_ID_EVENT = INSERT_ID_EVENT = 2 
};

The following table summarizes the relationship between event classes and type codes. Each class is derived from Log_event unless otherwise indicated. As can be seen, an event class is associated with a single type code in most cases, although there are some exceptions:

• Some classes are not associated with any type code because they are used only as a base class for which to derive subclasses or because they are never written to binary or relay logs or sent from master to slave. For example, Log_event has no type code because it is used only as a base class.

• A class may be associated with multiple type codes: Load_log_event may contain a type code of either LOAD_EVENT or NEW_LOAD_EVENT.

Value	Type Code	Class
		Log_event Base class for most other classes
		Muted_query_log_event Added in 5.0.23 Removed in 6.0.4
		Rows_log_event Added in 5.1.5 Base class for Write_rows_log_event, Update_rows_log_event, Delete_rows_log_event
		Old_rows_log_event Added in 5.1.22 Base class for Write_rows_log_event_old, Update_rows_log_event_old, Delete_rows_log_event_old
0	UNKNOWN_EVENT	Unknown_log_event
1	START_EVENT_V3	Start_log_event_v3 Renamed from START_EVENT/Start_log_event in 5.0.0 Base class for Format_description_log_event
2	QUERY_EVENT	Query_log_event Base class for Execute_load_query_log_event
3	STOP_EVENT	Stop_log_event
4	ROTATE_EVENT	Rotate_log_event
5	INTVAR_EVENT	Intvar_log_event
6	LOAD_EVENT	Load_log_event Base class for Create_file_log_event
7	SLAVE_EVENT	Slave_log_event Added in 4.0.0
8	CREATE_FILE_EVENT	Create_file_log_event Added in 4.0.0 Derived from Load_log_event
9	APPEND_BLOCK_EVENT	Append_block_log_event Added in 4.0.0 Base class for Begin_load_query_log_event
10	EXEC_LOAD_EVENT	Execute_load_log_event Added in 4.0.0
11	DELETE_FILE_EVENT	Delete_file_log_event Added in 4.0.0
12	NEW_LOAD_EVENT	Load_log_event Added in 4.0.0
13	RAND_EVENT	Rand_log_event Added in 4.0.5
14	USER_VAR_EVENT	User_var_log_event Added in 4.1.0
15	FORMAT_DESCRIPTION_EVENT	Format_description_log_event Added in 5.0.0 Derived from Start_log_event_v3
16	XID_EVENT	Xid_log_event Added in 5.0.3
17	BEGIN_LOAD_QUERY_EVENT	Begin_load_query_log_event Added in 5.0.3 Derived from Append_block_log_event
18	EXECUTE_LOAD_QUERY_EVENT	Execute_load_query_log_event Added in 5.0.3 Derived from Query_log_event
19	TABLE_MAP_EVENT	Table_map_log_event Added in 5.1.5
20	PRE_GA_WRITE_ROWS_EVENT	Write_rows_log_event_old Added in 5.1.5 as WRITE_ROWS_EVENT/Write_rows_log_event and derived from Rows_log_event Renamed in 5.1.18 to PRE_GA_WRITE_ROWS_EVENT/Write_rows_log_event_old and derived from Write_rows_log_event As of 5.1.22, derived from Old_rows_log_event
21	PRE_GA_UPDATE_ROWS_EVENT	Update_rows_log_event_old Added in 5.1.5 as UPDATE_ROWS_EVENT/Update_rows_log_event and derived from Rows_log_event Renamed in 5.1.18 to PRE_GA_UPDATE_ROWS_EVENT/Update_rows_log_event_old and derived from Update_rows_log_event As of 5.1.22, derived from Old_rows_log_event
22	PRE_GA_DELETE_ROWS_EVENT	Delete_rows_log_event_old Added in 5.1.5 as DELETE_ROWS_EVENT/Delete_rows_log_event and derived from Rows_log_event Renamed in 5.1.18 to PRE_GA_DELETE_ROWS_EVENT/Delete_rows_log_event_old and derived from Delete_rows_log_event As of 5.1.22, derived from Old_rows_log_event
23	WRITE_ROWS_EVENT	Write_rows_log_event Derived from Rows_log_event Renumbered in 5.1.18 from 20 to 23
24	UPDATE_ROWS_EVENT	Update_rows_log_event Derived from Rows_log_event Renumbered in 5.1.18 from 21 to 24
25	DELETE_ROWS_EVENT	Delete_rows_log_event Derived from Rows_log_event Renumbered in 5.1.18 from 22 to 25
26	INCIDENT_EVENT	Incident_log_event Added in 5.1.18
27	HEARTBEAT_LOG_EVENT	Heartbeat_log_event Added in 6.0.5