CASSANDRA-21072: Prevent TombstoneOverwhelmingException from being swallowed when tracking warnings

[arnav-chakraborty]

PR Description:

Prevent TombstoneOverwhelmingException from being swallowed when tracking warnings

Summary

In ReadCommandVerbHandler.doVerb(), when trackWarnings=true, all RejectException subclasses are caught and swallowed — an empty success response is sent with failure info in MessageParams. While the coordinator eventually
recognizes the failure via the side-channel params, TombstoneOverwhelmingException is a hard abort that should propagate as a proper failure response, not masquerade as a success.

The fix adds || e instanceof TombstoneOverwhelmingException to the catch block so it is always re-thrown. Other RejectException subclasses (LocalReadSizeTooLargeException, QueryReferencingTooManyIndexesException) continue
using the MessageParams path since they're designed for WarningContext aggregation.

Related datastax commit pr --> datastax@f1223ec

patch by Arnav Chakraborty; for CASSANDRA-21072

Co-authored-by: Arnav Chakraborty arnav251035@gmail.com

[Copilot]

Pull request overview

This PR ensures TombstoneOverwhelmingException is not swallowed when TRACK_WARNINGS is enabled in ReadCommandVerbHandler, so the exception propagates as a proper failure instead of being turned into an “empty success” response with side-channel MessageParams.

Changes:

• Update ReadCommandVerbHandler.doVerb() to rethrow TombstoneOverwhelmingException even when warning tracking is enabled.
• Add unit tests verifying TombstoneOverwhelmingException propagates both with and without TRACK_WARNINGS.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/java/org/apache/cassandra/db/ReadCommandVerbHandler.java	Prevents TombstoneOverwhelmingException from being swallowed in the warning-tracking RejectException handling path.
test/unit/org/apache/cassandra/db/ReadCommandVerbHandlerTest.java	Adds regression tests ensuring tombstone aborts propagate regardless of warning tracking.

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[Copilot]

The new special-casing for TombstoneOverwhelmingException is covered by tests, but there is still no unit test asserting the opposite branch: when TRACK_WARNINGS is enabled and a different RejectException (e.g., LocalReadSizeTooLargeException / QueryReferencingTooManyIndexesException) is thrown, doVerb should swallow it and send an empty success response with the corresponding MessageParams populated. Adding a test for this would protect against future regressions in the warning-tracking path.