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https://issues.apache.org/jira/browse/CASSANDRA-20480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17938057#comment-17938057
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Matt Byrd commented on CASSANDRA-20480:
---------------------------------------
PR for trunk here:
https://github.com/apache/cassandra/pull/4007
> Avoid system keyspace truncation record access blocking on interval tree
> builds
> -------------------------------------------------------------------------------
>
> Key: CASSANDRA-20480
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20480
> Project: Apache Cassandra
> Issue Type: Improvement
> Reporter: Matt Byrd
> Assignee: Matt Byrd
> Priority: Normal
> Time Spent: 10m
> Remaining Estimate: 0h
>
> A call to SystemKeyspace::removeEndpoint may block for extended periods of
> time behind an interval tree build since it does a blocking flush, explained
> in a bit more detail here:
> https://issues.apache.org/jira/browse/CASSANDRA-19597
> This in turn takes the synchronized monitor lock on SystemKeyspace.class and
> blocks various other methods from executing, including in particular
> SystemKeyspace::getTruncationRecord, which is called on various hot paths to
> determine whether to drop/filter mutations, (Commitlog replay, Hints,
> Batchlog and also committing Paxos transactions)
> This can cause a continuous stream of timeouts while operations are on-going
> ( which are making calls to removeEndpoint).
> The vast majority of the time the truncation record would not have changed,
> since it's only updated when one truncates which is typically rare.
> If we factor out the synchronization of the truncation record to a monitor on
> a static field, we avoid this problem, whilst still preventing various
> concurrency problems when operating on the SystemKeyspace field
> truncationRecords.
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