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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.
To assist with troubleshooting, InnoDB
temporarily enables standard InnoDB
Monitor
output under certain conditions. For more information, see
Section 15.20, “InnoDB Troubleshooting”.
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.
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.
To enable the InnoDB
Lock Monitor for
SHOW ENGINE INNODB
STATUS
output, you are only required to enable
innodb_status_output_locks
.
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.
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.
in the data directory and writes output to it every 15 seconds,
approximately.
pid
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.
file can become quite large over time.
pid
Document created the 26/06/2006, last modified the 26/10/2018
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