Log stanza of the qm.ini file

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 LogDefaults stanza of the mqs.ini file ). Change these settings only if we 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 we 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. We 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. We 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. Refer to the description of the LogType attribute in LogDefaults stanza of the mqs.ini file 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 Version 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 Windows.
    • /var/mqm/log in UNIX and Linux systems.

    We 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 we 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 we change the locations of these files, we 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 we can select DoubleWrite, but if you do so, the system interprets this as TripleWrite.

      SingleWrite
      We 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.

      See LogWriteIntegrity - using SingleWrite or TripleWrite for more information.

    LogManagement= Manual|Automatic | Archive
    The method used to manage log extents, either manually or by the queue manager.
    The attribute applies only when LogType is LINEAR.

    If we change the LogManagement value, the change does not take effect until the queue manager is restarted.

    If an unrecognized value for the attribute is found, the queue manager will not start until the value is corrected.

    The LogManagement property is not valid on IBM i.

      Manual
      You manage the log extents manually. Specifying this option means that the queue manager does not reuse or delete log extents, even when they are no longer required for recovery.

      Automatic
      Log extents are managed automatically by the queue manager. Specifying this option means that the queue manager is able to reuse or delete log extents as soon as they are no longer required for recovery. No allowance is made for archiving.

      Archive
      Log extents are managed by the queue manager, but we must notify the queue manager when archiving of each log extent is complete.

      Specify this option means that the queue manager is free to reuse or delete a log extent, as soon as the queue manager has been notified that an extent no longer required for recovery has been archived.

      You perform this notification using the RESET QMGR MQSC command or Reset Queue Manager PCF command.

  • LogWriteIntegrity - using SingleWrite or TripleWrite
    The setting of the LogWriteIntegrity option, in the Log stanza of the qm.ini file, determines the algorithm that is used by logger in IBM MQ to write out log records to the recovery log. The default setting is TripleWrite and this setting is both safe in almost every possible scenario

Parent topic: Attributes for changing queue manager configuration information