[CASSANDRA-19986] Prepared statements cache computation improvements

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 4.0.15, 4.1.8, 5.0.3, 5.1
• Component/s: Legacy/CQL
• Change Category: Performance
• Complexity: Normal
• Platform: All

Source Control Link

https://github.com/apache/cassandra/commit/ff54fd5ffd03846326862951e2a6de9b52de01f6

Test and Documentation Plan

See PR

• Assignee: Berenguer Blasi
• Reporter: Berenguer Blasi

Authors

Berenguer Blasi

Reviewers

Maxwell Guo, Stefan Miklosovic

• Created: 08/Oct/24 11:40
• Updated: 12/Nov/24 07:37
• Resolved: 04/Nov/24 09:07

Description

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

Issue Links

• causes: CASSANDRA-20055 Flaky PstmtPersistenceTest
• links to: CASSANDRA-19986 PR 4.0
• links to: CASSANDRA-19986 PR 4.1
• links to: CASSANDRA-19986 PR 5.0
• links to: CASSANDRA-19986 PR trunk