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https://issues.apache.org/jira/browse/CASSANDRA-21528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18103693#comment-18103693
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koo commented on CASSANDRA-21528:
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As you mentioned, this change alone may not make a big difference.
However, I also saw some small, low-risk patches included in 6.0. I thought
that, when combined with this patch, they could lead to meaningful results.
I have jfr file, but I cannot share them because company policy does not allow
any files to be sent outside the company. :(
Thank you, as always.
> Cache Enum.values() in ClusteringPrefix.Kind deserialization to avoid
> per-read array allocation
> -----------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-21528
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21528
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Legacy/Core
> Reporter: koo
> Assignee: koo
> Priority: Normal
> Fix For: 6.0-alpha2, 7.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> *description*
> When deserializing clusterings and range/slice bounds, the kind is resolved
> via Kind.values()[in.readByte()]:
> - ClusteringPrefix.java:616 — ClusteringPrefix.Deserializer (streaming
> path) // 5.0.7
>
> Enum.values() creates a new copy of its array every time it is called. So
> each time we read a clustering or a bound, a new Kind[] array is created just
> to look up one value by index, and then thrown away. This runs on the hot
> deserialization path, so it creates a lot of short-lived garbage for no real
> benefit.
>
> Impact (measured, JFR allocation profiling on a read/Paxos-LWT-heavy
> workload):
> - Total heap allocation observed: ~170 GB (120s)
> - ClusteringPrefix$Kind[]: ~5.22 GB (≈3.1%) of that total
> This garbage is short-lived, so GC pause impact under a modern collector is
> minimal and CPU cost is negligible; this is purely an allocation-pressure /
> GC-throughput improvement.
>
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