Queue manager logs

Use the Log queue manager properties page from the IBM® MQ Explorer, or the Log stanza in the qm.ini file, to specify information about logging on a queue manager.

By default, these settings are inherited from the settings specified for the default log settings for the queue manager (described in Log defaults for IBM MQ ). Change these settings only if you want to configure this queue manager in a different way.

For information about calculating log sizes, see Calculating the size of the log.

Note: The limits given in the following parameter list are set by IBM MQ. Operating system limits might reduce the maximum possible log size.

LogPrimaryFiles= 3 | 2-254 ( Windows )| 2-510 ( UNIX and Linux® systems)

The log files allocated when the queue manager is created.

The minimum number of primary log files you can have is 2 and the maximum is 254 on Windows, or 510 on UNIX and Linux systems. The default is 3.

The total number of primary and secondary log files must not exceed 255 on Windows, or 511 on UNIX and Linux systems, and must not be less than 3.

The value is examined when the queue manager is created or started. You can change it after the queue manager has been created. However, a change in the value is not effective until the queue manager is restarted, and the effect might not be immediate.

LogSecondaryFiles= 2 | 1-253 ( Windows )| 1-509 ( UNIX and Linux systems)

The log files allocated when the primary files are exhausted.

The minimum number of secondary log files is 1 and the maximum is 253 on Windows, or 509 on UNIX and Linux systems. The default number is 2.

The total number of primary and secondary log files must not exceed 255 on Windows, or 511 on UNIX and Linux systems, and must not be less than 3.

The value is examined when the queue manager is started. You can change this value, but changes do not become effective until the queue manager is restarted, and even then the effect might not be immediate.

LogFilePages= number

The log data is held in a series of files called log files. The log file size is specified in units of 4 KB pages.

The default number of log file pages is 4096, giving a log file size of 16 MB.

On UNIX and Linux systems the minimum number of log file pages is 64, and on Windows the minimum number of log file pages is 32; in both cases the maximum number is 65 535.

Note: The size of the log files specified during queue manager creation cannot be changed for a queue manager.

LogType= CIRCULAR |LINEAR

The type of logging to be used by the queue manager. You cannot change the type of logging to be used once the queue manager has been created. Refer to the description of the LogType attribute in Log defaults for IBM MQ for information about creating a queue manager with the type of logging you require.

CIRCULAR: Start restart recovery using the log to roll back transactions that were in progress when the system stopped.
See Types of logging for a fuller explanation of circular logging.
LINEAR: For both restart recovery and media or forward recovery (creating lost or damaged data by replaying the contents of the log).
See Types of logging for a fuller explanation of linear logging.

LogBufferPages= 0 | 0-4096

The amount of memory allocated to buffer records for writing, specifying the size of the buffers in units of 4 KB pages.

The minimum number of buffer pages is 18 and the maximum is 4096. Larger buffers lead to higher throughput, especially for larger messages.

If you specify 0 (the default), the queue manager selects the size. In IBM WebSphere® MQ 7.1 this is 512 (2048 KB).

If you specify a number in the range 1 through 17, the queue manager defaults to 18 (72 KB). If you specify a number in the range 18 through 4096, the queue manager uses the number specified to set the memory allocated.

The value is examined when the queue manager is started. The value can be increased or decreased within the limits stated. However, a change in the value is not effective until the next time the queue manager is started.

LogPath= directory_name

The directory in which the log files for a queue manager reside. This must exist on a local device to which the queue manager can write and, preferably, on a different drive from the message queues. Specifying a different drive gives added protection in case of system failure.

The default is:

C:\ProgramData\IBM\MQ\log in IBM MQ for Windows.
/var/mqm/log in IBM MQ for UNIX and Linux systems.

You can specify the name of a directory on the crtmqm command using the -ld flag. When a queue manager is created, a directory is also created under the queue manager directory, and this is used to hold the log files. The name of this directory is based on the queue manager name. This ensures that the log file path is unique, and also that it conforms to any limitations on directory name lengths.

If you do not specify -ld on the crtmqm command, the value of the LogDefaultPath attribute is used.

In IBM MQ for UNIX and Linux systems, user ID mqm and group mqm must have full authorities to the log files. If you change the locations of these files, you must give these authorities yourself. This is not required if the log files are in the default locations supplied with the product.

LogWriteIntegrity=SingleWrite|DoubleWrite| TripleWrite

The method the logger uses to reliably write log records.

TripleWrite: This is the default method.
Note, that you can select DoubleWrite, but if you do so, the system interprets this as TripleWrite.
SingleWrite: You should use SingleWrite, only if the file-system and device hosting the IBM MQ recovery log explicitly guarantees the atomicity of 4KB writes.
That is, when a write of a 4KB page fails for any reason, the only two possible states are either the before image, or the after image. No intermediate state should be possible.

Note: If there is sufficient concurrency in your persistent workload, there is minimal potential benefit in setting anything other than the default value, TripleWrite.