5.2.3 The General Query Log

The general query log is a general record of what mysqld is doing. The server writes information to this log when clients connect or disconnect, and it logs each SQL statement received from clients. The general query log can be very useful when you suspect an error in a client and want to know exactly what the client sent to mysqld.

mysqld writes statements to the query log in the order that it receives them, which might differ from the order in which they are executed. This logging order is in contrast with that of the binary log, for which statements are written after they are executed but before any locks are released. In addition, the query log may contain statements that only select data while such statements are never written to the binary log.

When using statement-based binary logging on a replication master server, statements received by its slaves are written to the query log of each slave. Statements are written to the query log of the master server if a client reads events with the mysqlbinlog utility and passes them to the server.

However, when using row-based binary logging, updates are sent as row changes rather than SQL statements, and thus these statements are never written to the query log when binlog_format is ROW. A given update also might not be written to the query log when this variable is set to MIXED, depending on the statement used. See Section 16.1.2.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”, for more information.

Control the general query log at server startup as follows:

• Before 5.1.6, the general query log destination is always a file. To enable the log, start mysqld with the --log[=file_name] or -l [file_name] option.

• As of MySQL 5.1.6, the destination can be a file or a table, or both. Start mysqld with the --log[=file_name] or -l [file_name] option to enable the general query log, and optionally use --log-output to specify the log destination (as described in Section 5.2.1, “Selecting General Query and Slow Query Log Output Destinations”).

• As of MySQL 5.1.12, as an alternative to --log or -l, use --general_log[={0|1}] to specify the initial general query log state. In this case, the default general query log file name is used. With no argument or an argument of 1, --general_log enables the log. With an argument of 0, this option disables the log.

• As of MySQL 5.1.29, use --general_log[={0|1}] to enable or disable the general query log, and optionally --general_log_file=file_name to specify a log file name. The --log and -l options are deprecated.

If the general query log file is enabled but no name is specified, the default name is host_name.log and the server creates the file in the same directory where it creates the PID file. If a name is given, the server creates the file in the data directory unless an absolute path name is given to specify a different directory.

To disable or enable the general query log or change the log file name at runtime, use the global general_log and general_log_file system variables. Set general_log to 0 (or OFF) to disable the log or to 1 (or ON) to enable it. Set general_log_file to specify the name of the log file. If a log file already is open, it is closed and the new file is opened.

When the general query log is enabled, the server writes output to any destinations specified by the --log-output option or log_output system variable. If you enable the log, the server opens the log file and writes startup messages to it. However, further logging of queries to the file does not occur unless the FILE log destination is selected. If the destination is NONE, the server writes no queries even if the general log is enabled. Setting the log file name has no effect on logging if the log destination value does not contain FILE.

Server restarts and log flushing do not cause a new general query log file to be generated (although flushing closes and reopens it). On Unix, you can rename the file and create a new one by using the following commands:

shell> mv host_name.log host_name-old.log
shell> mysqladmin flush-logs
shell> mv host_name-old.log backup-directory

On Windows, you cannot rename the general query log file while the server has it open before MySQL 5.1.3. You must stop the server, rename the file, and then restart the server to create a new log file.

As of MySQL 5.1.12, you can rename the general query log file at runtime by disabling the log:

SET GLOBAL general_log = 'OFF';

With the log disabled, rename the log file externally; for example, from the command line. Then enable the log again:

SET GLOBAL general_log = 'ON';

This method works on any platform and does not require a server restart.

The session sql_log_off variable can be set to ON or OFF to disable or enable general query logging for the current connection.

The general query log should be protected because logged statements might contain passwords. See Section 6.1.2.3, “Passwords and Logging”.