2-Binlog Event Header

All the binlog events stored in a binary log file have a common structure:

  • an event header
  • event data

Event Header Structure, 19 Bytes

Note: if CRC32 is in use, the Event Length is 4 bytes bigger in size.
The 4 bytes CRC32 are written at the end of the event (just after the last 'data' byte).

Event Type

Fake Events

These are generated on the fly, never written.

Event Flag

HexEvent flag description
0x0001LOG_EVENT_BINLOG_IN_USE_F

This flag only makes sense for Format_description_log_event. It is set
when the event is written, and *reset* when a binlog file is
closed (yes, it's the only case when MySQL modifies already written
part of binlog). Thus it is a reliable indicator that binlog was
closed correctly.
0x0002LOG_EVENT_FORCED_ROTATE_F

(unused)
0x0004LOG_EVENT_THREAD_SPECIFIC_F

If the query depends on the thread (for example: TEMPORARY TABLE)
0x0008LOG_EVENT_SUPPRESS_USE_F

Suppress the generation of 'USE' statements before the actual
statement. This flag should be set for any events that does not need
the current database set to function correctly. Most notable cases
are 'CREATE DATABASE' and 'DROP DATABASE'.
0x0010LOG_EVENT_UPDATE_TABLE_MAP_VERSION_F

(unused)
0x0020LOG_EVENT_ARTIFICIAL_F

Artificial events are created arbitarily and not written to binary log.
These events should not update the master log position when slave
SQL thread executes them.
0x0040LOG_EVENT_RELAY_LOG_F

Events with this flag set are created by slave IO thread and written to relay log
0x0080LOG_EVENT_IGNORABLE_F

For an event, 'e', carrying a type code, that a slave,
's', does not recognize, 's' will check 'e' for
LOG_EVENT_IGNORABLE_F, and if the flag is set, then 'e'
is ignored. Otherwise, 's' acknowledges that it has
found an unknown event in the relay log.
0x0100LOG_EVENT_NO_FILTER_F

(no description yet)
0x0200LOG_EVENT_MTS_ISOLATE_F

(no description yet)
0x8000LOG_EVENT_SKIP_REPLICATION_F

Flag set by application creating the event (with @@skip_replication);
the slave will skip replication of such events
if --replicate-events-marked-for-skip is not set to REPLICATE.
This is a MariaDB flag; we allocate it from the end of the available
values to reduce risk of conflict with new MySQL flags.

Event Header example of FORMAT_DESCRIPTION_EVENT

This is the first event in the binlog file at pos 4

a4 85 9e 59 0f 8c 27 00  00 f5 00 00 00 f9 00 00  ...Y..'.........
00 00 00 04 00 31 30 2e  31 2e 32 34 2d 4d 61 72  .....10.1.24-Mar
69 61 44 42 00 6c 6f 67  00 00 00 00 00 00 00 00  iaDB.log....
...
...

Interpretation of First 19 Bytes of the Event (the Event Header)

  • a4 85 9e 59 [4] Timestamp => 59 9e 85 a4 => 1503561124 = 2017-08-24 09:52:04
  • 0f [1] Event Type = 0x0f = FORMAT_DESCRIPTION_EVENT
  • 8c 27 00 00 [4] Server_id => 00 00 27 8c = 10124
  • f5 00 00 00 [4] Event length => 00 00 00 f5 => 245
  • f9 00 00 00 [4] Next Event pos => 00 00 00 f9 => 249 (pos 4 + event size)
  • 00 00 [2] Event flags = 0

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