MySQL Server has several different logs that can help you find out what activity is taking place.
| Log Type | Information Written to Log |
|---|---|
| Error log | Problems encountered starting, running, or stopping mysqld |
| General query log | Established client connections and statements received from clients |
| Binary log | All statements that change data (also used for replication) |
| Relay log | Data changes received from a replication master server |
| Slow query log | All 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”.