[jira] [Created] (CASSANDRA-20804) Optimize DataPlacement lookup by ReplicationParams

["Dmitry Konstantinov (Jira)" <ji...@apache.org>]

Dmitry Konstantinov created CASSANDRA-20804:
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             Summary: Optimize DataPlacement lookup by ReplicationParams
                 Key: CASSANDRA-20804
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-20804
             Project: Apache Cassandra
          Issue Type: Improvement
          Components: Consistency/Coordination, Transactional Cluster Metadata
            Reporter: Dmitry Konstantinov
            Assignee: Dmitry Konstantinov
         Attachments: image-2025-07-30-18-39-40-063.png

When we execute a plain write to identify replicas we do several lookups from ClusterMetadata.placements map using ReplicationParams.
Equals and hashcode for ReplicationParams objects are not very cheap, so there is a noticible overhead for this logic in CPU profile (0.77% of overall CPU usage for a plain write Cassandra stress test):
!image-2025-07-30-18-39-40-063.png|width=700!

To reduce it the following optimisations can be applied:
 # Avoid double lookup in of the same DataPlacement in forNonLocalStrategyTokenRead and forNonLocalStrategyTokenWrite
 # Memorize hashCode value
 # Deduplicate ReplicationParams to use the same objects in DataPlacements and KeyspaceMetadata to use the fast == path in the equals

The last two optimizations are safe because ReplicationParams is immutable.
Note: it is related to TCM logic, so it is trunk only issue.



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