What logs look like

Logs consist of primary and secondary files, and a control file. You define the number and size of log files and where they are stored in the file system.

An IBM® MQ log consists of two components:
  1. One or more files of log data.
  2. A log control file
A file of log data is also known as a log extent.

There are a number of log extents that contain the data being recorded. You can define the number and size (as explained in Log defaults for IBM MQ), or take the system default of three primary and two secondary extents.

Each of the three primary and two secondary extents defaults to 16 MB.

When you create a queue manager, the number of log extents pre-allocated is the number of primary log extents allocated. If you do not specify a number, the default value is used.

IBM MQ uses two types of logging:
  • Circular
  • Linear

    The number of log extents used with linear logging can be very large, depending on the frequency of your media image recording.

See Types of logging for more information.

In IBM MQ for Windows, if you have not changed the log path, log extents are created under the directory: 

C:\ProgramData\IBM\MQ\log\<QMgrName>
In IBM MQ for UNIX and Linux® systems, if you have not changed the log path, log extents are created under the directory: 

/var/mqm/log/<QMgrName>

IBM MQ starts with these primary log extents, but if the primary log space is not sufficient, it allocates secondary log extents. It does this dynamically and removes them when the demand for log space reduces. By default, up to two secondary log extents can be allocated. You can change this default allocation, as described in Changing IBM MQ and queue manager configuration information.