MySQL Reference Manual

The MySQL Log Files

MySQL has several different log files that can help you find out what’s going on inside mysqld:

Log file	Description
The error log	Problems encountered when starting, running, or stopping mysqld.
The isam log	Logs all changes to the ISAM tables. Used only for debugging the isam code.
The query log	Established connections and executed queries.
The update log	Deprecated: stores all statements that change data.
The binary log	Stores all statements that change something. Used also for replication.
The slow log	Stores all queries that took more than long_query_time to execute or didn’t use indexes.

All logs can be found in the mysqld data directory. You can force mysqld to reopen the log files (or in some cases switch to a new log) by executing FLUSH LOGS. See Section 4.5.3.

The Error Log

mysqld writes all errors to the stderr, which the safe_mysqld script redirects to a file called 'hostname'.err. (On Windows, mysqld writes this directly to \mysql\data\mysql.err.)

This contains information indicating when mysqld was started and stopped and also any critical errors found when running. If mysqld dies unexpectedly and safe_mysqld needs to restart mysqld, safe_mysqld will write a restarted mysqld row in this file. This log also holds a warning if mysqld notices a table that needs to be automatically checked or repaired.

On some operating systems, the error log will contain a stack trace that can be used to find out where mysqld died. See Section D.1.4.

The General ...