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https://issues.apache.org/jira/browse/CASSANDRA-15006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16768374#comment-16768374
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Benedict commented on CASSANDRA-15006:
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Hi [~jborgstrom],
The {{DirectByteBufferR}} simply means it is a read only byte buffer. This
might be mapped. Unfortunately, given conflation of terms around
{{BufferPool}} it is hard to understand what your graphs mean. Could you
explicitly define them for me? What does each graph title directly map to; how
is it being produced?
I would not bother truncating any table. Ideally, we would get a heap dump
posted somewhere privately for us to download and analyse.
> Possible java.nio.DirectByteBuffer leak
> ---------------------------------------
>
> Key: CASSANDRA-15006
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15006
> Project: Cassandra
> Issue Type: Bug
> Environment: cassandra: 3.11.3
> jre: openjdk version "1.8.0_181"
> heap size: 2GB
> memory limit: 3GB (cgroup)
> I started one of the nodes with "-Djdk.nio.maxCachedBufferSize=262144" but
> that did not seem to make any difference.
> Reporter: Jonas Borgström
> Priority: Major
> Attachments: CASSANDRA-15006-reference-chains.png,
> Screenshot_2019-02-04 Grafana - Cassandra.png, Screenshot_2019-02-14 Grafana
> - Cassandra(1).png, Screenshot_2019-02-14 Grafana - Cassandra.png
>
>
> While testing a 3 node 3.11.3 cluster I noticed that the nodes were suddenly
> killed by the Linux OOM killer after running without issues for 4-5 weeks.
> After enabling more metrics and leaving the nodes running for 12 days it sure
> looks like the
> "java.nio:type=BufferPool,name=direct" Mbean shows a very linear growth
> (approx 15MiB/24h, see attached screenshot). Is this expected to keep growing
> linearly after 12 days with a constant load?
>
> In my setup the growth/leak is about 15MiB/day so I guess in most setups it
> would take quite a few days until it becomes noticeable. I'm able to see the
> same type of slow growth in other production clusters even though the graph
> data is more noisy.
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