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MySQL 5.7 Reference Manual  /  ...  /  Enabling InnoDB Monitors

15.17.2 Enabling InnoDB Monitors

When you enable InnoDB monitors for periodic output, InnoDB writes their output to the mysqld server standard error output (stderr). In this case, no output is sent to clients. When switched on, InnoDB monitors print data about every 15 seconds. Server output usually is directed to the error log (see Section 6.4.2, “The Error Log”). This data is useful in performance tuning. On Windows, start the server from a command prompt in a console window with the --console option if you want to direct the output to the window rather than to the error log.

InnoDB sends diagnostic output to stderr or to files rather than to stdout or fixed-size memory buffers, to avoid potential buffer overflows. 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 innodb_status.pid, where pid is the server process ID. InnoDB removes the file for a normal shutdown. If abnormal shutdowns have occurred, instances of these status files may be present and must be removed manually. Before removing them, you might want to examine them to see whether they contain useful information about the cause of abnormal shutdowns. The innodb_status.pid file is created only if the configuration option innodb-status-file=1 is set.

InnoDB monitors should be enabled only when you actually want to see monitor information because output generation does result in some performance decrement. Also, if you enable monitor output, your error log may become quite large if you forget to disable it later.

Note

To assist with troubleshooting, InnoDB temporarily enables standard InnoDB Monitor output under certain conditions. For more information, see Section 15.21, “InnoDB Troubleshooting”.

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

=====================================
2014-10-16 18:37:29 0x7fc2a95c1700 INNODB MONITOR OUTPUT
=====================================

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 and disable InnoDB Monitors.

Enabling the Standard InnoDB Monitor

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

set GLOBAL innodb_status_output=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.

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:

mysql> SHOW ENGINE INNODB STATUS\G

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

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 InnoDBLock 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:

set GLOBAL innodb_status_output=ON;
set GLOBAL innodb_status_output_locks=ON;

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

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.

Note

To enable the InnoDB Lock Monitor for SHOW ENGINE INNODB STATUS output, you are only required to enable innodb_status_output_locks.


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