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https://issues.apache.org/jira/browse/CASSANDRA-1358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895439#action_12895439
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Jonathan Ellis commented on CASSANDRA-1358:
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Yes, unbounding those would also be required in the get-rid-of-MDP scenario.
In short, the bound never makes things better and can make things worse.
(But, if you are running into that 4096 bound -- as I predicted earlier :) --
your node is already _severely_ overwhelmed and the only thing we are
discussing is how to mitigate the effects, this is not going to stop it from
timing out a ton of requests under those conditions.)
> Clogged RRS/RMS stages can hold up processing of gossip messages and request
> acks
> ---------------------------------------------------------------------------------
>
> 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
> 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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