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https://issues.apache.org/jira/browse/CASSANDRA-13265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15888439#comment-15888439
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Christian Esken commented on CASSANDRA-13265:
---------------------------------------------
Here is one possibly very important observation. It looks like Coalescing is
doing an infinite loop while doing maybeSleep(). I checked 10 Thread dumps, and
in each of them the Thread was at the same location. Is it possible that
averageGap is 0? This would lead to infinite recursion.
{code}
private static boolean maybeSleep(int messages, long averageGap, long
maxCoalesceWindow, Parker parker)
{
// only sleep if we can expect to double the number of messages we're
sending in the time interval
long sleep = messages * averageGap; // TODO can averageGap be 0 ?
if (sleep > maxCoalesceWindow)
return false;
// assume we receive as many messages as we expect; apply the same
logic to the future batch:
// expect twice as many messages to consider sleeping for "another"
interval; this basically translates
// to doubling our sleep period until we exceed our max sleep window
while (sleep * 2 < maxCoalesceWindow)
sleep *= 2; // <<<<<<<<<<<<<<<< CoalescingStrategies:106
parker.park(sleep);
return true;
}
{code}
If sum is bigger than MEASURED_INTERVAL, then averageGap() returns 0. I am
aware that this is highly unlikely, but I cannot explain the likely hanging in
maybeSleep() line 106.
{code}
private long averageGap()
{
if (sum == 0)
return Integer.MAX_VALUE;
return MEASURED_INTERVAL / sum;
}
{code}
> Communication breakdown in OutboundTcpConnection
> ------------------------------------------------
>
> 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
> 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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