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https://issues.apache.org/jira/browse/CASSANDRA-1358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895421#action_12895421
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Jonathan Ellis commented on CASSANDRA-1358:
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(getting rid of MDP would also slightly reduce the object allocations on the
network path, since we're not wrapping the work in a separate Task object and
involving the extra executor queue. So I would expect a minor performance
benefit as well.)
> Message deserializer pool will never grow beyond a single thread.
> -----------------------------------------------------------------
>
> Key: CASSANDRA-1358
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1358
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.5
> Environment: All.
> Reporter: Mike Malone
> Priority: Minor
> Fix For: 0.6.5
>
>
> The message deserialization process can become a bottleneck that prevents
> efficient resource utilization because the executor that manages the
> deserialization process will never grow beyond a single thread. The message
> deserializer executor is instantiated in the MessagingService constructor as
> a JMXEnableThreadPoolExecutor, which extends
> java.util.concurrent.ThreadPoolExecutor. The thread pool is instantiated with
> a corePoolSize of 1 and a maximumPoolSize of
> Runtime.getRuntime().availableProcessors(). But, according to the
> ThreadPoolExecutor documentation "using an unbounded queue (for example a
> LinkedBlockingQueue without a predefined capacity) will cause new tasks to be
> queued in cases where all corePoolSize threads are busy. Thus, no more than
> corePoolSize threads will ever be created. (And the value of the
> maximumPoolSize therefore doesn't have any effect.)"
> The message deserializer pool uses a LinkedBlockingQueue, so there will never
> be more than one deserialization thread. This issue became a problem in our
> production cluster when the MESSAGE-DESERIALIZER-POOL began to back up on a
> node that was only lightly loaded. We increased the core pool size to 4 and
> the situation improved, but the deserializer pool was still backing up while
> the machine was not fully utilized (less than 100% CPU utilization). This
> leads me to think that the deserializer thread is blocking on some sort of
> I/O, which seems like it shouldn't happen.
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