The Binary Log

• The binary log contains all statements that update data or potentially could have updated it.
  • Statements are stored in the form of "events" that describe the modifications.
  • It also contains information about how long each statement took that updated data.
  • It is not used for statements such as SELECT or SHOW that do not modify data.

• The primary purpose of the binary log is to be able to update databases during a restore operation as fully as possible, because it contains all updates done after a backup was made.

• The binary log is also used on master replication servers as a record of the statements to be sent to slave servers.
  • If using the binary log for replication do not remove binary logs until their contents have been processed by all slaves.

• To enable the binary log, start mysqld with the --log-bin[=name].
  • If no name value is given, mysqld uses the hostname followed by -bin and writes the file in the data directory.

• Running the server with the binary log enabled makes performance about 1% slower.
  • The benefits of the binary log for restore operations and setting up replication outweigh this minor performance decrement.

What is the maximum size of binary logs?

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© 2007 John Michael Pierobon

Notes