[jira] [Updated] (CASSANDRA-21459) Eliminate per-row enum array allocation in cursor compaction clustering deserialization

["Jon Haddad (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-21459?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jon Haddad updated CASSANDRA-21459:
-----------------------------------
    Resolution: Duplicate
        Status: Resolved  (was: Triage Needed)

> Eliminate per-row enum array allocation in cursor compaction clustering deserialization
> ---------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-21459
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-21459
>             Project: Apache Cassandra
>          Issue Type: Sub-task
>          Components: Local/Compaction
>            Reporter: Jon Haddad
>            Assignee: Jon Haddad
>            Priority: Normal
>
> {{ClusteringPrefix.Kind.values()}} is called once per row read ({{ClusteringDescriptor.loadClustering}}, both call sites) and once per range tombstone marker written ({{SSTableCursorWriter.writeRangeTombstone}}). Java clones the enum constants array on every {{values()}} call, so the cursor compaction path — which is intended to be allocation-free per row — allocates a fresh ~40-byte {{Kind[]}} for every row read from every source sstable and for every range tombstone marker written.
> The fix caches the array once in a {{static final}} field ({{Kind.ALL_KINDS}}) and indexes into the shared copy at the three cursor hot-path sites.
> Found via JFR allocation profiling ({{jdk.ObjectAllocationInNewTLAB}}/{{OutsideTLAB}} with stack traces) during cursor compaction: with the patch, the {{ClusteringPrefix$Kind[]}} allocation site disappears from the profile entirely. In an allocation-scaling measurement comparing a 1,200-row compaction against a 12,000-row compaction, allocation growth drops from 1,487,448 to 449,488 bytes; the remainder is attributable to test-environment {{Ref}} debug tracking and chunk-cache machinery rather than cursor code.
> The same {{values()}} pattern exists on the iterator deserialization path ({{ClusteringPrefix.serializer}}, three sites). Those are left unchanged here to keep this patch minimal and scoped to the cursor path; they can be addressed separately if desired.



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