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MySQL 5.5 Reference Manual  /  ...  /  Enabling InnoDB Monitors

14.20.2 Enabling InnoDB Monitors

When InnoDB monitors are enabled for periodic output, InnoDB writes the output to the mysqld server standard error output (stderr). InnoDB sends diagnostic output to stderr rather than to stdout or fixed-size memory buffers to avoid potential buffer overflows.

On Windows, stderr is directed to the default log file unless configured otherwise. If you want to direct the output to the console window rather than to the error log, start the server from a command prompt in a console window with the --console option. For more information, see Section, “Error Logging on Windows”.

On Unix and Unix-like systems, stderr is typically directed to the terminal unless configured otherwise. For more information, see Section, “Error Logging on Unix and Unix-Like Systems”.

When enabled, InnoDB monitors print data about every 15 seconds. This data is useful in performance tuning. As a side effect, the output of SHOW ENGINE INNODB STATUS is written to a status file in the MySQL data directory every fifteen seconds. The name of the file is, where pid is the server process ID. InnoDB removes the file when the server is shut down normally. If abnormal shutdowns have occurred, instances of these status files may be present and must be removed manually. Before removing the files, examine them to see if they contain useful information about the cause of abnormal shutdowns. An file is only created if the innodb-status-file configuration option is enabled. It is disabled by default.

InnoDB monitors should only be enabled when you actually want to see monitor information because output generation causes some performance decrement. Also, if monitor output is directed to the error log, the log may become quite large if you forget to disable the monitor later by dropping the monitor table.


To assist with troubleshooting, InnoDB temporarily enables standard InnoDB Monitor output under certain conditions. For more information, see Section 14.23, “InnoDB Troubleshooting”.

Each monitor begins with a header containing a timestamp and the monitor name. For example:


The header for the standard InnoDB Monitor (INNODB MONITOR OUTPUT) is also used for the Lock Monitor because the latter produces the same output with the addition of extra lock information.

Enabling an InnoDB monitor for periodic output involves using a CREATE TABLE statement to create a specially named InnoDB table that is associated with the monitor. For example, to enable the standard InnoDB Monitor, you would create an InnoDB table named innodb_monitor.

Using CREATE TABLE syntax is just a way to pass a command to the InnoDB engine through MySQL's SQL parser. The only things that matter are the table name and that it be an InnoDB table. The structure of the table and the database where the table is created are not relevant. If you shut down the server, the monitor does not restart automatically when you restart the server. Drop the monitor table and issue a new CREATE TABLE statement to start the monitor.

The PROCESS privilege is required to enable or disable InnoDB Monitors.

Enabling the Standard InnoDB Monitor

To enable the standard InnoDB Monitor for periodic output, create the innodb_monitor table:


To disable the standard InnoDB Monitor, drop the table:

DROP TABLE innodb_monitor;

Obtaining Standard InnoDB Monitor Output On Demand

As an alternative to enabling the standard InnoDB Monitor for periodic output, you can obtain standard InnoDB Monitor output on demand using the SHOW ENGINE INNODB STATUS SQL statement, which fetches the output to your client program. If you are using the mysql interactive client, the output is more readable if you replace the usual semicolon statement terminator with \G:


SHOW ENGINE INNODB STATUS output also includes InnoDB Lock Monitor data if the InnoDB Lock Monitor is enabled.

Enabling the InnoDB Lock Monitor

To enable the InnoDB Lock Monitor for periodic output, create the innodb_lock_monitor table:

CREATE TABLE innodb_lock_monitor (a INT) ENGINE=INNODB;

To disable the InnoDB Lock Monitor, drop the table:

DROP TABLE innodb_lock_monitor;

Enabling the InnoDB Tablespace Monitor

To enable the InnoDB Tablespace Monitor for periodic output, create the innodb_tablespace_monitor table:

CREATE TABLE innodb_tablespace_monitor (a INT) ENGINE=INNODB;

To disable the standard InnoDB Tablespace Monitor, drop the table:

DROP TABLE innodb_tablespace_monitor;

Enabling the InnoDB Table Monitor

To enable the InnoDB Table Monitor for periodic output, create the innodb_table_monitor table:

CREATE TABLE innodb_table_monitor (a INT) ENGINE=INNODB;

To disable the InnoDB Table Monitor, drop the table:

DROP TABLE innodb_table_monitor;

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