MySQL 8.4.2
Source Code Documentation
Binlog Event

The events contain the actual data that should be shipped from the master to the slave.

Depending on the use, different events are sent.

Binlog Management

The first event is either a START_EVENT_V3 or a FORMAT_DESCRIPTION_EVENT while the last event is either a STOP_EVENT or ROTATE_EVENT.

START_EVENT_V3

Binlog::START_EVENT_V3:
TypeNameDescription
int<2> binlog-version Version of the binlog format. See Binlog Version
string[50] mysql-server version version of the MySQL Server that created the binlog. The string is evaluated to apply workarounds on the slave.
int<4> create-timestamp seconds since Unix epoch when the binlog was created

FORMAT_DESCRIPTION_EVENT

A format description event is the first event of a binlog for binlog Version 4. It described how the other events are laid out.

Note
Added in MySQL 5.0.0 as a replacement for START_EVENT_V3.
Payload
TypeNameDescription
int<2> binlog-version Version of the binlog format. See Binlog Version
string[50] mysql-server version version of the MySQL Server that created the binlog. The string is evaluated to apply workarounds on the slave.
int<4> create-timestamp seconds since Unix epoch when the binlog was created

int<1>

event-header-length

Length of the Binlog Event Header of next events. Should always be 19.

string<EOF>

event type header lengths

a array indexed by binlog-event-type - 1 to extract the length of the event specific header

Example
$ hexdump -v -s 4 -C relay-bin.000001
00000004 82 2d c2 4b 0f 02 00 00 00 67 00 00 00 6b 00 00 |.-.K.....g...k..|
00000014 00 00 00 04 00 35 2e 35 2e 32 2d 6d 32 00 00 00 |.....5.5.2-m2...|
00000024 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000034 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000044 00 00 00 00 00 00 00 82 2d c2 4b 13 38 0d 00 08 |........-.K.8...|
00000054 00 12 00 04 04 04 04 12 00 00 54 00 04 1a 08 00 |..........T.....|
00000064 00 00 08 08 08 02 00 |........ |
hexdump
void hexdump(void *p, long length)

For mysql-5.5.2-m2 the event specific header lengths are:

Event NameHeader Length
v4v3v1
Binlog Event Header 1913
START_EVENT_V3 56
QUERY_EVENT 1311
STOP_EVENT 0
ROTATE_EVENT 80
INTVAR_EVENT 0
LOAD_EVENT 18
SLAVE_EVENT 0
CREATE_FILE_EVENT 4
APPEND_BLOCK_EVENT 4
EXEC_LOAD_EVENT 4
DELETE_FILE_EVENT 4
NEW_LOAD_EVENT 18
RAND_EVENT 0
USER_VAR_EVENT 0
FORMAT_DESCRIPTION_EVENT 84—
XID_EVENT 0—
BEGIN_LOAD_QUERY_EVENT 4—
EXECUTE_LOAD_QUERY_EVENT 26—
TABLE_MAP_EVENT 8—
DELETE_ROWS_EVENTv0 0—
UPDATE_ROWS_EVENTv0 0—
WRITE_ROWS_EVENTv0 0—
INCIDENT_EVENT 2—
HEARTBEAT_EVENT 0—
DELETE_ROWS_EVENTv2 10—
UPDATE_ROWS_EVENTv2 10—
WRITE_ROWS_EVENTv2 10—

The event-size of 0x67 (103) minus the event-header length of 0x13 (19) should match the event type header length of the FORMAT_DESCRIPTION_EVENT 0x54 (84).

The number of events understood by the master may differ from what the slave supports. It is calculated by:

event_size - event_header_length - 2 - 50 - 4 - 1

For mysql-5.5.2-m2 it is 0x1b (27).

STOP_EVENT

A STOP_EVENT has not payload or post-header

ROTATE_EVENT

The rotate event is added to the binlog as last event to tell the reader what binlog to request next.

Post-header
TypeNameDescription
if binlog-version > 1 {
int<8> position
}
Payload
TypeNameDescription
string<EOF> binlog name of the next binlog

SLAVE_EVENT

Note
Ignored !

INCIDENT_EVENT

Payload
TypeNameDescription
int<2> type
HexName
0x0000INCIDENT_NONE
0x0001INCIDENT_LOST_EVENTS
int<1> message_length Length of message
binary<var> message Incident message with length message_length

HEARTBEAT_EVENT

An artificial event generated by the master. It isn't written to the relay logs.

It is added by the master after the replication connection was idle for x seconds to update the slave's Seconds_behind_source timestamp in the SHOW REPLICA STATUS output.

It has no payload nor post-header.

Statement Based Replication Events

Statement Based Replication or SBR sends the SQL queries a client sent to the master AS IS to the slave. It needs extra events to mimic the client connection's state on the slave side.

QUERY_EVENT

The query event is used to send text queries through the binlod

Post-header
TypeNameDescription
int<4> slave_proxy_id
int<4> execution time
int<1> schema length
int<2> error code
if binlog-version >= 4 {
int<2> status_vars length Number of bytes in the following sequence of status_vars
}
Payload
TypeNameDescription
binary<var> status-vars

A sequence of status key/value pairs. The key is 1-byte, while the value is dependent on the key

HexFlagValue Length
0x00Q_FLAGS2_CODE 4
0x01Q_SQL_MODE_CODE 8
0x02Q_AUTO_INCREMENT 1 + n + 1
0x03Q_CATALOG 2 + 2
0x04Q_CHARSET_CODE 2 + 2 + 2
0x05Q_TIME_ZONE_CODE 1 + 1
0x06Q_CATALOG_NZ_CODE 1 + n
0x07Q_LC_TIME_NAMES_CODE 2
0x08Q_CHARSET_DATABASE_CODE 2
0x09Q_TABLE_MAP_FOR_UPDATE_CODE 8
0x0aQ_SOURCE_DATA_WRITTEN_CODE 4
0x0bQ_INVOKERS 1 + n + 1 + n
0x0cQ_UPDATED_DB_NAMES 1 + n*nul-term-string
0x0dQ_MICROSECONDS 3

The value of the different status vars are:

Q_FLAGS2_CODE

Bitmask of flags that are usually set with the SET command:

SQL_AUTO_IS_NULL FOREIGN_KEY_CHECKS UNIQUE_CHECKS AUTOCOMMIT

HexFlag
0x00004000OPTION_AUTO_IS_NULL
0x00080000OPTION_NOT_AUTOCOMMIT
0x04000000OPTION_NO_FOREIGN_KEY_CHECKS
0x08000000OPTION_RELAXED_UNIQUE_CHECKS

Q_SQL_MODE_CODE

Bitmask of flags that are usually set with SET sql_mode:

HexFlag
0x00000001MODE_REAL_AS_FLOAT
0x00000002MODE_PIPES_AS_CONCAT
0x00000004MODE_ANSI_QUOTES
0x00000008MODE_IGNORE_SPACE
0x00000010MODE_NOT_USED
0x00000020MODE_ONLY_FULL_GROUP_BY
0x00000040MODE_NO_UNSIGNED_SUBTRACTION
0x00000080MODE_NO_DIR_IN_CREATE
0x00000100MODE_POSTGRESQL
0x00000200MODE_ORACLE
0x00000400MODE_MSSQL
0x00000800MODE_DB2
0x00001000MODE_MAXDB
0x00002000MODE_NO_KEY_OPTIONS
0x00004000MODE_NO_TABLE_OPTIONS
0x00008000MODE_NO_FIELD_OPTIONS
0x00010000MODE_MYSQL323
0x00020000MODE_MYSQL40
0x00040000MODE_ANSI
0x00080000MODE_NO_AUTO_VALUE_ON_ZERO
0x00100000MODE_NO_BACKSLASH_ESCAPES
0x00200000MODE_STRICT_TRANS_TABLES
0x00400000MODE_STRICT_ALL_TABLES
0x00800000MODE_NO_ZERO_IN_DATE
0x01000000MODE_NO_ZERO_DATE
0x02000000MODE_INVALID_DATES
0x04000000MODE_ERROR_FOR_DIVISION_BY_ZERO
0x08000000MODE_TRADITIONAL
0x10000000MODE_NO_AUTO_CREATE_USER
0x20000000MODE_HIGH_NOT_PRECEDENCE
0x40000000MODE_NO_ENGINE_SUBSTITUTION
0x80000000MODE_PAD_CHAR_TO_FULL_LENGTH

Q_AUTO_INCREMENT

2 byte autoincrement-increment and 2 byte autoincrement-offset

Note
Only written if the -increment is > 1

Q_CATALOG

1 byte length + <length> chars of the cataiog + ‘0‘-char

Note
Only written if length > 0

Q_CHARSET_CODE

2 bytes character_set_client + 2 bytes collation_connection + 2 bytes collation_server

See Character Set

Q_TIME_ZONE_CODE

1 byte length + <length> chars of the timezone.

Timezone the master is in.

Note
only written when length > 0

Q_CATALOG_NZ_CODE

1 byte length + <length> chars of the catalog.

Note
only written when length > 0

Q_LC_TIME_NAMES_CODE

LC_TIME of the server. Defines how to parse week-, month and day-names in timestamps

Note
only written when length > 0

Q_CHARSET_DATABASE_CODE

character set and collation of the schema

Q_TABLE_MAP_FOR_UPDATE_CODE

a 64bit field ... should only be used in Row Based Replication Events and multi-table updates

Q_MASTER_DATA_WRITTEN_CODE

4 byte ...

Q_INVOKERS

1 byte length + <length> bytes username and 1 byte length + <length> bytes hostname

Q_UPDATED_DB_NAMES

1 byte count + <count> \0 terminated string

Q_MICROSECONDS

3 byte microseconds

binary<var> schema
binary<eof> query text of the query

INTVAR_EVENT

RAND_EVENT

USER_VAR_EVENT

XID_EVENT

Row Based Replication Events

In Row Based replication the changed rows are sent to the slave which removes side-effects and makes it more reliable. Now all statements can be sent with RBR though. Most of the time you will see RBR and SBR side by side.

TABLE_MAP_EVENT

DELETE_ROWS_EVENTv0

UPDATE_ROWS_EVENTv0

WRITE_ROWS_EVENTv0

DELETE_ROWS_EVENTv2

UPDATE_ROWS_EVENTv2

WRITE_ROWS_EVENTv2

LOAD INFILE replication

LOAD DATA|XML INFILE is a special SQL statement as it has to ship the files over to the slave too to execute the statement.

LOAD_EVENT

CREATE_FILE_EVENT

APPEND_BLOCK_EVENT

EXEC_LOAD_EVENT

DELETE_FILE_EVENT

NEW_LOAD_EVENT

BEGIN_LOAD_QUERY_EVENT

EXECUTE_LOAD_QUERY_EVENT

A binlog event starts with Binlog Event Header and is followed by a event specific part.

Binlog Event Header

The binlog event header starts each event and is either 13 or 19 bytes long, depending on the Binlog Version

Binlog::EventHeader:
TypeNameDescription
int<4> timestamp seconds since unix epoch
int<1> event_type See mysql::binlog::event::Log_event_type
int<4> server-id server-id of the originating mysql-server. Used to filter out events in circular replication
int<4> event-size size of the event (header, post-header, body)
if binlog-version > 1 {
int<4> log-pos position of the next event
int<2> flags See Binlog Event Header Flags