Components

What follows is a description of the components required to enable distributed queuing with queue-sharing groups.

Listeners

The group LU 6.2 and TCP/IP listeners listen on an address that is logically connected to the generic address.

For the LU 6.2 listener, the specified LUGROUP is mapped to the VTAM generic resource associated with the queue-sharing group. For an example of setting up this technology, see Table 32 .

For the TCP/IP listener, the specifed port has two mutually exclusive means of being connected to the generic address:

• In the case of a front-end router such as the IBM Network dispatcher (see Network Dispatcher User's Guide, GC31-8496-03), inbound connect requests are forwarded from the router to the members of the queue-sharing group.
• In the case of TCP/IP WLM/DNS, each listener registers as being part of the WLM group. This is a registration type model, similar to the VTAM generic resource for LU 6.2. For an example of setting up this technology, see Using WLM/DNS. WLM/DNS only maps hostname and does not map port numbers. This means that all the group listeners in a queue-sharing group must use the same port number. Use the WebSphere MQ command (MQSC) as shown in the following examples:
  • On queue manager QM1:

    START LSTR PORT(2424) INDISP(GROUP) +
    IPADDR(QM1.MACH.IBM.COM)
    

  • On queue manager QM2:

    START LSTR PORT(2424) INDISP(GROUP) +
    IPADDR(QM2.MACH.IBM.COM)
    

Transmission queues and triggering

A shared transmission queue is used to store messages before they are moved from the queue-sharing group to the destination. It is a shared queue and it is accessible to all queue managers in the queue-sharing group.

Triggering

A triggered shared queue can generate more than one trigger message for a satisfied trigger condition. There is one trigger message generated for each local initiation queue defined on a queue manager in the queue-sharing group associated with the triggered shared queue.

In the case of distributed queuing, each channel initiator receives a trigger message for a satisfied shared transmission queue trigger condition. However, only one channel initiator will actually process the triggered start, and the others will fail safely. The triggered channel is then started with a load balanced start (see Load-balanced channel start) that will be triggered to start channel QSG.TO.QM2. To create a shared transmission queue, use the WebSphere MQ commands (MQSC) as shown in the following example:

DEFINE QLOCAL(QM2) DESCR('Transmission queue to QM2') +
USAGE(XMITQ) QSGDISP(SHARED) +
CFSTRUCT(APPLICATION1) INITQ(SYSTEM.CHANNEL.INITQ) +
TRIGGER TRIGDATA(QSG.TO.QM2)

Message channel agents

A channel can only be started on a channel initiator if it has access to a channel definition for a channel with that name. A channel definition can be defined to be private to a queue manager or stored on the shared repository and available anywhere (a group definition). This means that a group defined channel is available on any channel initiator in the queue-sharing group.

Note:

The private copy of the group definition can be changed or deleted.

To create group channel definitions, use the WebSphere MQ commands (MQSC) as shown in the following examples:

DEFINE CHL(QSG.TO.QM2) CHLTYPE(SDR) +
TRPTYPE(TCP) CONNAME(QM2.MACH.IBM.COM) +
XMITQ(QM2) QSGDISP(GROUP)

DEFINE CHL(QM2.TO.QSG) CHLTYPE(RCVR) TRPTYPE(TCP) +
QSGDISP(GROUP)

There are two perspectives from which to look at the message channel agents used for distributed queuing with queue-sharing groups:

• Inbound
• Outbound

Inbound

An inbound channel is a shared channel if it is connected to the queue manager through the group listener. It is connected either through the generic interface to the queue-sharing group, then directed to a queue manager within the group, or targeted at a specific queue manager's group port or the luname used by the group listener.

Outbound

An outbound channel is a shared channel if it moves messages from a shared transmission queue. In the above example commands, sender channel QSG.TO.QM2 is a shared channel because its transmission queue, QM2 is defined with QSGDISP(SHARED).

Synchronization queue

Shared channels have their own shared synchronization queue called SYSTEM.QSG.CHANNEL.SYNCQ, which is accessible to any member of the queue-sharing group. (Private channels continue to use the private synchronization queue. See Synchronization queue) This means that the channel can be restarted on a different queue manager and channel initiator instance within the queue-sharing group in the event of failure of the communications subsystem, channel initiator or queue manager. (See Shared channel recovery for details.)

DQM with queue-sharing groups requires that a shared queue is available with the name SYSTEM.QSG.CHANNEL.SYNCQ. This queue must be available so that a group listener can successfully start.

If a group listener fails because the queue was not available, the queue can be defined and the listener can be restarted without recycling the channel initiator, and the non-shared channels are not affected.

Make sure that you define this queue using INDXTYPE(MSGID). This will improve the speed at which they can be accessed.