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From "Christian Esken (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13265) Expiration in OutboundTcpConnection can block the reader Thread
Date Tue, 11 Apr 2017 15:29:41 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15964522#comment-15964522
] 

Christian Esken commented on CASSANDRA-13265:
---------------------------------------------

Done.  2 organizational topics left:

I will add the required line to the commit message. Looks OK?!?
 bq. patch by Christian Esken; reviewed by Ariel Weisberg  and Jason Brown for CASSANDRA-13265
My proposals for the CHANGES.txt would be the following text. Can you do that, Ariel? I do
not know in which versions to add that, as they are upcoming versions.
 bq. Expire OutboundTcpConnection messages by a single Thread 

Here are the branches.The cassandra-3.0 is already squashed. If that branch is OK, I will
also squash the other 3 branches.

https://github.com/christian-esken/cassandra/commits/cassandra-3.0
https://github.com/christian-esken/cassandra/commits/cassandra-3.11
https://github.com/christian-esken/cassandra/commits/trunk
https://github.com/christian-esken/cassandra/commits/cassandra-2.2

> Expiration in OutboundTcpConnection can block the reader Thread
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-13265
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13265
>             Project: Cassandra
>          Issue Type: Bug
>         Environment: Cassandra 3.0.9
> Java HotSpot(TM) 64-Bit Server VM version 25.112-b15 (Java version 1.8.0_112-b15)
> Linux 3.16
>            Reporter: Christian Esken
>            Assignee: Christian Esken
>             Fix For: 3.0.x
>
>         Attachments: cassandra.pb-cache4-dus.2017-02-17-19-36-26.chist.xz, cassandra.pb-cache4-dus.2017-02-17-19-36-26.td.xz
>
>
> I observed that sometimes a single node in a Cassandra cluster fails to communicate to
the other nodes. This can happen at any time, during peak load or low load. Restarting that
single node from the cluster fixes the issue.
> Before going in to details, I want to state that I have analyzed the situation and am
already developing a possible fix. Here is the analysis so far:
> - A Threaddump in this situation showed  324 Threads in the OutboundTcpConnection class
that want to lock the backlog queue for doing expiration.
> - A class histogram shows 262508 instances of OutboundTcpConnection$QueuedMessage.
> What is the effect of it? As soon as the Cassandra node has reached a certain amount
of queued messages, it starts thrashing itself to death. Each of the Thread fully locks the
Queue for reading and writing by calling iterator.next(), making the situation worse and worse.
> - Writing: Only after 262508 locking operation it can progress with actually writing
to the Queue.
> - Reading: Is also blocked, as 324 Threads try to do iterator.next(), and fully lock
the Queue
> This means: Writing blocks the Queue for reading, and readers might even be starved which
makes the situation even worse.
> -----
> The setup is:
>  - 3-node cluster
>  - replication factor 2
>  - Consistency LOCAL_ONE
>  - No remote DC's
>  - high write throughput (100000 INSERT statements per second and more during peak times).
>  



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