Message store

Local queues require a message store to store their messages. Each queue can specify what type of store to use, and where it is located. Use the queue characteristic Queue_FileDesc to specify the type of message store and to provide parameters for it. The field type is ascii and the value must be a file descriptor of the form:

adapter class:adapter parameters
or
adapter alias:adapter parameters

For example:
MsgLog:d:\QueueManager\ServerQM12\Queues

MQe Version 2.1 provides two adapters, one for writing messages to disk and one for storing them in memory. By creating an appropriate adapter, messages can be stored in any suitable place or medium (such as DB2® database or writable CDs).

The choice of adapter determines the persistence and resilience of messages. For instance if a memory adapter is used then the messages are only as resilient as the memory. Memory may be a much faster medium than disk but is highly volatile compared to disk. Hence the choice of adapter is an important one.

If you do not provide message store information when creating a queue, it defaults to the message store that was specified when the queue manager was created.

Take the following into consideration when setting the Queue_FileDesc field:
  • Ensure that the correct syntax is used for the system that the queue resides on. For instance, on a Windows® system use "\" as a file separator. On UNIX® systems use "/" as a file separator. In some cases it may be possible to use either but this is dependent on the support provided by the JVM (Java™ Virtual Machine) that the queue manager runs in. As well as file separator differences, some systems use drive letters (like Windows NT®) whereas others (like UNIX) do not.
  • On some systems it is possible to specify relative directories (" .\"), whilst on others it is not. Even on those where relative directories can be specified, they should be used with great caution as the current directory can be changed during the lifetime of the JVM. Such a change causes problems when interacting with queues using relative directories.

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