BingLogEvent
每个LogEvent分为Header、Post-Header、Body、EventFooter四部分, Header和Footer每个event都相同格式，但PostHeader和Body，不同EventType不一样。
@anchor Binary_log_event_format
Any @c Binary_log_event saved on disk consists of the following four
components.
- Common-Header
- Post-Header
- Body
- Footer
Common header has the same format and length in a given MySQL version. It is
documented @ref Table_common_header "here".
The Body may be of different format and length even for different events of
the same type. The binary formats of Post-Header and Body are documented
separately in each subclass.
Footer is common to all the events in a given MySQL version. It is documented
@ref Table_common_footer "here".
EventHeader
EventHeader为固定长度19字节，主要记录了event的创建时间、类型、大小、在日志中的偏移量等信息.
各字段详细说明参考： Log_event_header
EventType
/**
Enumeration type for the different types of log events.
*/
enum Log_event_type {
/**
Every time you add a type, you have to
- Assign it a number explicitly. Otherwise it will cause trouble
if a event type before is deprecated and removed directly from
the enum.
- Fix Format_description_event::Format_description_event().
*/
UNKNOWN_EVENT = 0,
/*
Deprecated since mysql 8.0.2. It is just a placeholder,
should not be used anywhere else.
*/
START_EVENT_V3 = 1,
QUERY_EVENT = 2,
STOP_EVENT = 3,
ROTATE_EVENT = 4,
INTVAR_EVENT = 5,
SLAVE_EVENT = 7,
APPEND_BLOCK_EVENT = 9,
DELETE_FILE_EVENT = 11,
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,
/**
The V1 event numbers are used from 5.1.16 until mysql-5.6.
*/
WRITE_ROWS_EVENT_V1 = 23,
UPDATE_ROWS_EVENT_V1 = 24,
DELETE_ROWS_EVENT_V1 = 25,
/**
Something out of the ordinary happened on the master
*/
INCIDENT_EVENT = 26,
/**
Heartbeat event to be send by master at its idle time
to ensure master's online status to slave
*/
HEARTBEAT_LOG_EVENT = 27,
/**
In some situations, it is necessary to send over ignorable
data to the slave: data that a slave can handle in case there
is code for handling it, but which can be ignored if it is not
recognized.
*/
IGNORABLE_LOG_EVENT = 28,
ROWS_QUERY_LOG_EVENT = 29,
/** Version 2 of the Row events */
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,
TRANSACTION_CONTEXT_EVENT = 36,
VIEW_CHANGE_EVENT = 37,
/* Prepared XA transaction terminal event similar to Xid */
XA_PREPARE_LOG_EVENT = 38,
/**
Extension of UPDATE_ROWS_EVENT, allowing partial values according
to binlog_row_value_options.
*/
PARTIAL_UPDATE_ROWS_EVENT = 39,
TRANSACTION_PAYLOAD_EVENT = 40,
HEARTBEAT_LOG_EVENT_V2 = 41,
/**
Add new events here - right above this comment!
Existing events (except ENUM_END_EVENT) should never change their numbers
*/
ENUM_END_EVENT /* end marker */
};
目前总共的事件类型有41种，部分是老版本使用的。最常见的有TABLE_MAP_EVENT、QUERY_EVENT、WRITE_ROWS_EVENT、UPDATE_ROWS_EVENT和DELETE_ROWS_EVENT等。
EventFooter
EventFooter主要是描述checksum算法，校验算法主要是CRC32
/**
Enumeration spcifying checksum algorithm used to encode a binary log event
*/
enum enum_binlog_checksum_alg {
/**
Events are without checksum though its generator is checksum-capable
New Master (NM).
*/
BINLOG_CHECKSUM_ALG_OFF = 0,
/** CRC32 of zlib algorithm */
BINLOG_CHECKSUM_ALG_CRC32 = 1,
/** the cut line: valid alg range is [1, 0x7f] */
BINLOG_CHECKSUM_ALG_ENUM_END,
/**
Special value to tag undetermined yet checksum or events from
checksum-unaware servers
*/
BINLOG_CHECKSUM_ALG_UNDEF = 255
};
Events
TableMapEvent
mysql对一行数据做修改时，会产生两个Event: TableMapEvent和RowsEvent(Write_rows_event/Update_rows_event/Delete_rows_event)。TABLE_MAP_EVENT描述了表的结构信息。
In row-based mode, every row operation event is preceded by a Table_map_event which maps a table definition to a number.
The table definition consists of database name, table name, and column definitions.
Post-Header部分包括两部分: table_id和flags，flags目前属于保留位。table_id是递增的，每次修改表结构都会产生Table_map_event，并分配新的table_id。
Body部分包括了库名、表名、列数、列字段类型以及每列的详细信息。其中metadata根据列的类型不同而不同，有些类型没有的。
RowsEvent
RowsEvent是row模式下，insert/update/delete事件的基类，其Post-Header主要是包含table_id信息。
而body部分，则根据操作不同，决定是否包含更新前后的数据columns_before_image/columns_after_image。
