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https://issues.apache.org/jira/browse/CASSANDRA-19986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17887872#comment-17887872
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Maxwell Guo commented on CASSANDRA-19986:
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Any test data or jstack information about the performance improvements before
and after the change, and the fact that this change has no impact on other
scenarios.
> Prepared statements cache computation improvements
> --------------------------------------------------
>
> Key: CASSANDRA-19986
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19986
> Project: Cassandra
> Issue Type: Improvement
> Components: Legacy/CQL
> Reporter: Berenguer Blasi
> Assignee: Berenguer Blasi
> Priority: Normal
> Fix For: 4.0.x, 4.1.x, 5.0.x, 5.1
>
>
> Currently prepared statements size are computed twice which is duplicate
> effort:
> -
> [https://github.com/apache/cassandra/blob/cassandra-4.0/src/java/org/apache/cassandra/cql3/QueryProcessor.java#L672]
> -
> [https://github.com/apache/cassandra/blob/cassandra-4.0/src/java/org/apache/cassandra/cql3/QueryProcessor.java#L802]
> But we also get the side effect of that 'slow' computation locking the
> underlying ConcurrentHashMap. We've had nodes becoming unresponsively slow
> for hours with hundreds of threads in jstack all queued up behind
> {{computeIfAbsent}} operations on cache insertion/eviction collisions.
> Computing size only once and pulling that value instead of recomputing it on
> cache insertion was the solution
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