15.16.2 Enabling InnoDB Monitors

When InnoDB monitors are enabled for periodic output, InnoDB writes the output to mysqld server standard error output (stderr) every 15 seconds, approximately.

InnoDB sends the monitor 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 Error Logging on Windows.

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

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.

InnoDB monitor output 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.

The innodb_status_output and innodb_status_output_locks system variables are used to enable the standard InnoDB Monitor and InnoDB Lock Monitor.

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

Enabling the Standard InnoDB Monitor

Enable the standard InnoDB Monitor by setting the innodb_status_output system variable to ON.

To disable the standard InnoDB Monitor, set innodb_status_output to OFF.

When you shut down the server, the innodb_status_output variable is set to the default OFF value.

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Enabling the InnoDB Lock Monitor

InnoDB Lock Monitor data is printed with the InnoDB Standard Monitor output. Both the InnoDB Standard Monitor and InnoDB Lock Monitor must be enabled to have InnoDB Lock Monitor data printed periodically.

To enable the InnoDB Lock Monitor, set the innodb_status_output_locks system variable to ON. Both the InnoDB standard Monitor and InnoDB Lock Monitor must be enabled to have InnoDB Lock Monitor data printed periodically:

To disable the InnoDB Lock Monitor, set innodb_status_output_locks to OFF. Set innodb_status_output to OFF to also disable the InnoDB Standard Monitor.

When you shut down the server, the innodb_status_output and innodb_status_output_locks variables are set to the default OFF value.

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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.

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Directing Standard InnoDB Monitor Output to a Status File

Standard InnoDB Monitor output can be enabled and directed to a status file by specifying the --innodb-status-file option at startup. When this option is used, InnoDB creates a file named innodb_status.pid in the data directory and writes output to it every 15 seconds, approximately.

InnoDB removes the status file when the server is shut down normally. If an abnormal shutdown occurs, the status file may have to be removed manually.

The --innodb-status-file option is intended for temporary use, as output generation can affect performance, and the innodb_status.pid file can become quite large over time.