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5.2.1 Selecting General Query and Slow Query Log Output Destinations »
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5.2. MySQL Server Logs

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5.2.1. Selecting General Query and Slow Query Log Output Destinations
5.2.2. The Error Log
5.2.3. The General Query Log
5.2.4. The Binary Log
5.2.5. The Slow Query Log
5.2.6. Server Log Maintenance

MySQL has several different logs that can help you find out what is going on inside mysqld.

Log Type Information Written to Log
The error log Problems encountered starting, running, or stopping mysqld
The general query log Established client connections and statements received from clients
The binary log All statements that change data (also used for replication)
The slow query log All queries that took more than long_query_time seconds to execute or didn't use indexes

By default, all log files are created in the mysqld data directory. You can force mysqld to close and reopen the log files (or in some cases switch to a new log) by flushing the logs. Log flushing occurs when you issue a FLUSH LOGS statement or execute a mysqladmin flush-logs, mysqladmin refresh, mysqldump --flush-logs, or mysqldump --master-data command. See Section 12.4.6.3, “FLUSH Syntax”, Section 4.5.2, “mysqladmin — Client for Administering a MySQL Server”, and Section 4.5.4, “mysqldump — A Database Backup Program”. In addition, the binary log is flushed when its size reaches the value of the max_binlog_size system variable.

If you are using MySQL replication capabilities, slave replication servers maintain additional log files called relay logs. Chapter 16, Replication, discusses relay log contents and configuration.

The server can write general query and slow query entries to log tables, log files, or both. For details, see Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”.

You can also control during runtime the general query and slow query logs. You can enable or disable logging, or change the name of the log file. See Section 5.2.3, “The General Query Log”, and Section 5.2.5, “The Slow Query Log”.

See Section 5.3.2.1, “Administrator Guidelines for Password Security”, for information about keeping logs secure.

MySQL Enterprise.  The MySQL Enterprise Monitor provides a number of advisors specifically related to the various log files. For more information, see http://www.mysql.com/products/enterprise/advisors.html.