MQ Log Files and its Importance

What are transaction logs?

    Provide the write ahead logging for WebSphere® MQ

    Transaction logs consist of two components

    Three or more files of log data

• S0000000.LOG – S9999999.LOG

Log control file

• amqhlctl.lfh

Default location of logs

UNIX: /var/mqm/log/<qmname>

Windows: C:\Program Files\IBM\WebSphere MQ\log\<qm name

MQ transaction logs contain

a   Transaction activity(Units of Work) and persistent messages

      Internal data about queue manager objects

c    Persistent channel status

Logging parameters

      There are several WMQ parameters which control operation of logging

      Logging parameters can have a significant effect on performance characteristics

      Some logging parameters can only be set at queue manager creation

      Parameters changeable after creation require a queuemanager restart

Log type

      Linear or circular logging must be selected at queue manager creation time  –lc option  for circular logging (default) and –ll option for linear logging

Primary log files

     Specifies the initial, minimum number of log files

     Primary log files specified by the –lp parameter of the crtmqm command

1   Default 3 ; Minimum 2 ; Maximum 510 Unix; Maximum 254 Windows

    Can be altered after queue manager creation

Secondary log files

    Specifies the additional log files which can be created should primary logs become full

    Secondary log files specified by the –ls parameter of the crtmqm command

1  Default 2 ;  Minimum 1 ; Maximum 509 Unix ; Maximum 253 Windows

   Can be altered after queue manager creation

Log file size

        Size of log file is specified as a number of 4KB pages

        Log file size may not be altered after queue manager creation

        Log file size specified by the –lf parameter of the crtmqm command

Default logging configuration

UNIX : /var/mqm/mqs.ini

When and how are transaction logs created?

Transaction logs are created at the same time as the queue manager

crtmqm contains flags that dictate which logging configuration to create

Flags:

• -lc , -ll , -ld , -lf , -lp , -ls .

Side-by-side comparisons

The following slides compare circular and linear logging in action, illustrating:

1       Primary and secondary log files

2       Active log files – those required for restart recovery

3       Inactive log files – log files no longer needed for restart recovery

Linear Logging inactive files

What about log file 0 and 1 in the example?

Although not required for restart they may be required for recovery

AMQ7467: The oldest log file required to start queue manager MYQMGR is S0000002.LOG.

AMQ7468: The oldest log file required to perform media recovery of queue manager MYQMGR is S0000000.LOG.

Log Management linear logging

1   Physical file management 

     Space management:  Moving/removing unnecessary files

2   Recording object images: Using rcdmqimg command

Log Management Circular: No log management required by the user

Log Recovery Scenarios

1    Power loss/Reboot/Queue Manager Failure : Restart Queue manager

      Queues are restored to their committed state at the time of the failure

      Persistent data is NOT lost

• Non-persistent messages will be discarded

Disk Failures:

Circular logging

• Restore queue manager and log files from latest back up [or]  Rebuild queue manager using SupportPac MS03

Linear logging

• Recover damaged objects with rcrmqobj  [ or ]  Restore queue manager from latest back up

Recovery of damaged objects :

Circular:  No object recovery is available

Linear:  Media recovery function

 rcdmqimg to record media image and  rcrmqobj to recover/recreate object from media image.