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https://issues.apache.org/jira/browse/CASSANDRA-13265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15923915#comment-15923915
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Christian Esken commented on CASSANDRA-13265:
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bq. This is not quite correct you can't count drainCount as dropped because
some of the drained messages may have been sent during iteration.
I looked in more detail, and I think this a flaw in the original code
"suggested" me to do this: {{drainedMessages.clear()}} is called twice, and
one time would be enough. IMO it would be better to only keep the one at the
end of the method and also do the drop-counting for the drained messages there.
This would also cover a rather exotic case of the {{catch (Exception e)}} in
the {{run()}} method. If an Exception is thrown, then there is a danger of
nothing being counted.
bq. Using a boxed integer
bq. You shouldn't need the check for null?
>From a brief check, this refers to a similar point. I saw many configuration
>options to allow null and followed that route. I am absolutely happy to make
>it non-boxed.
bq. The right way to do it is create a branch for all the versions where this
is going to be fixed. Start at 2.2, merge to 3.0, merge to 3.11, then merge to
trunk.
At Github? I can do so. But no PR, right? I saw it mentioned that one should
not open PR's for Cassandra on Github as they cannot be handled (it's just a
mirror).
> 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: 2.2.x, 3.0.x, 3.11.x, 4.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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