Tuesday, June 29, 2010

ActiveMQ pooling: a pool by any other name would smell as sweet

Working with a FUSE customer today who voiced confusion at all the different ways you can do a pooled connection factory in ActiveMQ. With confusion comes fear, uncertainty and distrust. Should I be using Jencks? Or should I be using the Spring CachedConnectionFactory? Wasn't there something on the activemq-pool documentation that said it didn't actually pool consumers? Help!

I took this confusion directly to the source, and had an enlightening discussion with James Strachan and Gary Tully at FuseSourceabout this. As a nice drop off, we ended up updating the documentation on Camel ActiveMQ, ActiveMQ Spring Support, and the Javadoc for the org.apache.activemq.pool.PooledConnectionFactory.

The bottom line is this: while Jencks was recommended in the past, it's no longer necessary as you can just use the org.apache.activemq.pool.PooledConnectionFactory from activemq-pool project. Alternatively, you can of course use the Spring CachedConnectionFactory, as outlined in this great article.

Here's the real sneaky thing though: the JavaDoc documentation of org.apache.activemq.pool.PooledConnectionFactory suggested that this connection factory doesn't pool consumers. This is in fact not not a drawback or a failing: it simply doesn't make sense to 'pool' JMS consumers. Maintain a collection of them for concurrent consumption in parallel? Sure! But keep a 'pool' of consumers, whereby you return consumers into the pool for reuse later on when you're finished? Don't do it! It simply doesn't make much sense - and, at a technical level - could end up creating havoc as the 'idle' consumers would still get messages delivered to their internal 'prefetch' queues, where they'd dwell until the consumer is activated again. We updated the documentation to better explain what the PooledConnectionFactory does.

We realized that the confusion comes from a number of outdated resources on the web that mentioned a myriad combination of ways to do pooling. That, and, the fact that it's easy to confuse the different concepts of 'pooling' and simply maintaining a collection of resources: the former involves sharing and reuse, while the latter does not.

Bottom line: forget about Jencks. Use activemq-pool's PooledConnection or Springs CachedConnectionFactory to manage your connection, session and producer pools. And don't go talking about 'consumer pools' - it really doesn't make sense - talk about 'collections of consumers'.

1 comment:

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