5.2. MySQL Server Logs

MySQL Server has several different logs that can help you find out what activity is taking place.

Log TypeInformation Written to Log
Error logProblems encountered starting, running, or stopping mysqld
General query logEstablished client connections and statements received from clients
Binary logAll statements that change data (also used for replication)
Relay logData changes received from a replication master server
Slow query logAll queries that took more than long_query_time seconds to execute or did not use indexes

By default, all log files are created in the data directory. You can force the server to close and reopen the log files (or in some cases switch to a new log file) 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.

The relay log is used only on slave replication servers, to hold data changes from the master server that must also be made on the slave. For discussion of relay log contents and configuration, see Section 17.2.2.1, “The Slave Relay Log”.

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”.

For information about log maintenance operations such as expiration of old log files, see Section 5.2.6, “Server Log Maintenance”.

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

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