Redpaper - IBM Redbooks
Redpaper - IBM Redbooks
Redpaper - IBM Redbooks
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2.4 Message Broker flow design<br />
2.4.1 Affinities<br />
Advantages Disadvantages<br />
Messages are pulled from the queue,<br />
rather than pushed onto another queue<br />
managers clustered queue. Thus, if a<br />
Message Broker becomes inoperative,<br />
messages do not build up on the queue<br />
manager serving the broker. Instead, the<br />
messages remain on the shared queue to<br />
be picked up by a functional broker.<br />
The ability to fully utilize the available<br />
resources as shared queues allows<br />
messages to be shared across available<br />
LPARS.<br />
Ability to take advantage of cloned<br />
applications and identically configured<br />
brokers by allowing less busy applications<br />
and brokers to retrieve messages from the<br />
shared queue at there own pace, thus<br />
reducing the risk of bottlenecks.<br />
Ability to take advantage of the<br />
serialization mechanism to ensure backed<br />
out units of work are completed in the<br />
correct order.<br />
Limitation of the coupling facility storage<br />
that no more than eight million messages<br />
can be stored on a queue.<br />
Non-persistent messages which could<br />
survive queue manager restarts can be an<br />
issue for the application. If an application<br />
depends on non-persistent messages not<br />
surviving a queue manager restart, it is<br />
possible you will need to add functionality<br />
to deal with this issue.<br />
Depending on how the coupling facility is<br />
being used, the storage taken up by<br />
shared queues could well be relatively<br />
expensive.<br />
There are a number of points to keep in mind with HA in the design of message<br />
flows.<br />
Message affinities can arise when multiple messages are required to make up a<br />
single business transaction or when messages must be processed in a specific<br />
order. This situation is also true when a Message Broker is forced to keep state,<br />
as is the case when using the aggregation node. This type of situation can often<br />
mean that a particular queue manager or Message Broker is required to process<br />
these messages. In terms of HA, this affinity can lead to vulnerabilities. If a<br />
particular queue manager or Message Broker is required to process a long string<br />
Chapter 2. Design decisions that affect high availability 17
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