Modifying IBM MQ queue files

From IBM® MQ 9.2.0, you can control the size of queue files using an attribute on local and model queues. You can display the current size of a queue file, and the maximum size it is currently able to grow to (based on the block size currently in use in that file), using two queue status attributes.

Attribute used to modify queue files

The attribute on local and model queues is:

MAXFSIZE: Denotes the maximum size of the queue file used by the queue, in megabytes.; See MAXFSIZE and Changing the size of an IBM MQ queue file for further information.; The PCF attribute for this attribute is MQIA_MAX_Q_FILE_SIZE; see Change, Copy, and Create Queue.

The two attributes on queue status are:

CURFSIZE: Displays the current size of the queue file in megabytes, rounded up to the nearest megabyte.; See CURFSIZE for more information.; The PCF attribute for this attribute is MQIA_CUR_Q_FILE_SIZE.
CURMAXFS: Indicates the current maximum size the queue file can grow to, rounded up to the nearest megabyte, given the current block size in use on a queue.; See CURMAXFS for more information.; The PCF attribute for this attribute is MQIA_CUR_MAX_FILE_SIZE.

See Inquire Queue and Inquire Queue (response) for further information on these two PCF attributes.

You can set and display these attributes using MQSC commands, IBM MQ Explorer, and the administrative REST API.

Note: You can only display the value of MAXFSIZE in the IBM MQ Console; you cannot configure the value.

Block size and granularity

Queue files are divided into segments called blocks. To increase the maximum size of a queue file, the block size or granularity of the queue might need to be changed by the queue manager.

If a newly defined queue is created with a large MAXFSIZE value, the queue is created with a suitable block size. However if an existing queue has its MAXFSIZE value increased, for example by using the ALTER QLOCAL command, it might be necessary to allow the queue to be emptied in order for the queue manager to reconfigure the queue.

See Calculating how much data an IBM MQ queue file can store for more information.

Attention: Some file systems and operating systems have limits on the size of the entire file system, or the size of an individual file. You should check the limits on the systems your enterprise uses.