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https://issues.apache.org/jira/browse/CASSANDRA-1358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895419#action_12895419
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Jonathan Ellis commented on CASSANDRA-1358:
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bq. So are the message deserializer threads blocking on a response from (or
pushing a task onto a queue for) a different thread pool then?
yes.
bq. If the intent is to have a single threaded executor, the second argument
should be 1
true, but possibly moot, because:
bq. it's unable to process gossip requests / responses in a timely manner
good point. we have a separate connection for gossip and acks so they won't be
blocked by a large request on the outbound path, but combining them both
through the same MDP on the inbound side defeats that to a large degree.
probably we should just get rid of MDP, and do the deserialize on the
IncomingTcpConnection thread. (This would require moving the flow control from
CASSANDRA-685 / CASSANDRA-1284 into RMVH / RVH.)
> 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: 0.6.3
> Environment: All.
> Reporter: Mike Malone
> Priority: Minor
>
> 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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