The Slow Query Log

• The slow query log consists of all SQL statements that took more than long_query_time seconds to execute.
  • The time to acquire the initial table locks is not counted as execution time.
  • mysqld writes a statement to the slow query log after it has been executed and after all locks have been released.
    • Log order might be different from execution order.
  • The minimum and default values of long_query_time are 1 and 10, respectively.

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

• The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization.
  • Examining a long slow query log can become a difficult task.
  • To make this easier, use the mysqldumpslow command to summarize the queries that appear in the log.
  • Use mysqldumpslow --help to see the options this command supports.

How do I perform server log maintenance?

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© 2007 John Michael Pierobon

Notes