The following section describes the benefits of shared queuing, which are:
A shared transmission queue can be serviced by an outbound channel running on any channel initiator in the queue-sharing group. Load-balanced channel start determines where a start channel command is targeted. An appropriate channel initiator is chosen that has access to the necessary communications subsystem. For example, a channel defined with TRPTYPE(LU6.2) will not be started on a channel initiator that only has access to a TCP/IP subsystem.
The choice of channel initiator is dependant on the channel load and the headroom of the channel initiator. The channel load is the number of active channels as a percentage of the maximum number of active channels allowed as defined in the channel initiator parameters. The headroom is the difference between the number of active channels and the maximum number allowed.
Inbound shared channels can be load-balanced across the queue-sharing group by use of a generic address, as described in Listeners.
The following table shows the types of shared-channel failure and how each type is handled.
| Type of failure: | What happens: |
| Channel initiator communications subsystem failure | The channels dependent on the communications subsystem enter channel retry, and are restarted on an appropriate queue-sharing group channel initiator by a load-balanced start command. |
| Channel initiator failure | The channel initiator fails, but the associated queue manager remains active. The queue manager monitors the failure and initiates recovery processing. |
| Queue manager failure | The queue manager fails (failing the associated channel initiator). Other queue managers in the queue-sharing group monitor the event and initiate peer recovery. |
| Shared status failure | Channel state information is stored in DB2, so a loss of connectivity to DB2 becomes a failure when a channel state change occurs. Running channels can carry on running without access to these resources. On a failed access to DB2, the channel enters retry. |
Client connection channels can benefit from the high availability of messages in queue-sharing groups that are connected to the generic interface instead of being connected to a specific queue manger. (For more information about this, see the WebSphere MQ Clients manual.)