koo created CASSANDRA-21528:
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Summary: 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
Reporter: koo
*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
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