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https://issues.apache.org/jira/browse/CASSANDRA-13756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16136625#comment-16136625
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Hannu Kröger commented on CASSANDRA-13756:
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Created a branch in https://issues.apache.org/jira/browse/CASSANDRA-13752 for
serialization fix.
> StreamingHistogram is not thread safe
> -------------------------------------
>
> Key: CASSANDRA-13756
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13756
> Project: Cassandra
> Issue Type: Bug
> Reporter: xiangzhou xia
> Assignee: Jeff Jirsa
> Fix For: 3.0.x, 3.11.x
>
>
> When we test C*3 in shadow cluster, we notice after a period of time, several
> data node suddenly run into 100% cpu and stop process query anymore.
> After investigation, we found that threads are stuck on the sum() in
> streaminghistogram class. Those are jmx threads that working on expose
> getTombStoneRatio metrics (since jmx is kicked off every 3 seconds, there is
> a chance that multiple jmx thread is access streaminghistogram at the same
> time).
> After further investigation, we find that the optimization in CASSANDRA-13038
> led to a spool flush every time when we call sum(). Since TreeMap is not
> thread safe, threads will be stuck when multiple threads visit sum() at the
> same time.
> There are two approaches to solve this issue.
> The first one is to add a lock to the flush in sum() which will introduce
> some extra overhead to streaminghistogram.
> The second one is to avoid streaminghistogram to be access by multiple
> threads. For our specific case, is to remove the metrics we added.
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