If you need to reserve a Sub-process pool for queued requests, you can define a test that will accept only queued requests by using the same Test Set as the Queue Manager. In the following example, the subprocess pool will not accept immediate requests, and its sub-processes will be dedicated to process queued transactions.

Then define a Test in a Sub-process pool Test Set, called test-queue:

If you need to reserve a Sub-process pool for immediate requests, see The maxConcurrentQueuedTransactions Attribute.