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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1358) Clogged RRS/RMS stages can hold up processing of gossip messages and request acks
Date Wed, 04 Aug 2010 21:58:16 GMT


Jonathan Ellis commented on CASSANDRA-1358:

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:
>             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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