What logs look like

A WebSphere 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 files that contain the data being recorded. You can define the number and size (as explained in Configuring WebSphere MQ), or take the system default of three files.

In WebSphere MQ for Windows, each of the three files defaults to 1 MB. In WebSphere MQ for UNIX systems, each of the three files defaults to 4 MB.

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

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

C:\Program Files\IBM\WebSphere MQ\log\<QMgrName>

In WebSphere MQ for UNIX systems, if you have not changed the log path, log files are created under the directory:

/var/mqm/log/<QMgrName>

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

The log control file

The log control file contains the information needed to control the use of log files, such as their size and location, the name of the next available file, and so on.

Note:
Ensure that the logs created when you start a queue manager are large enough to accommodate the size and volume of messages that your applications will handle. You will probably need to change the default log numbers and sizes to meet your requirements. For more information, see Calculating the size of the log.