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CASSANDRA-21390 trunk TrieMemtable MemtableReclaimMemory AssertionError: Negative released in MemtablePool$SubPool#4878

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CASSANDRA-21390 trunk TrieMemtable MemtableReclaimMemory AssertionError: Negative released in MemtablePool$SubPool#4878
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patch by <Authors>; reviewed by <Reviewers> for CASSANDRA-#####

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Co-authored-by: Name2 <email2>

The Cassandra Jira

smiklosovic and others added 2 commits June 12, 2026 10:20
…by an existing row deletion

When BTreeRow.merge reconciles an update into a row whose existing deletion
shadows the update's cells, it filtered the update (incoming) side of the merge
with Reconciler.retain, which records the removal via
PostReconciliationFunction.delete. On the memtable write path that subtracts the
shadowed cells' on-heap size from the allocator's ownership even though that
incoming data was never allocated to the memtable. Under overwrite/delete churn
that re-applies cells already covered by a newer row/partition deletion (e.g.
repair re-streaming), the allocator's "owns" counter drifts negative and the next
flush trips "AssertionError: Negative released" in MemtablePool$SubPool.released
via MemtableAllocator$SubAllocator.releaseAll during discard.

Filter the update (incoming) side with a non-recording variant,
Reconciler.retainWithoutRecordingRemoval, and keep retain() for the existing side,
whose data the memtable already owns. The filtered result is identical; only the
erroneous accounting notification is dropped. This mirrors the already-correct
complex-column path in ColumnData.merge.

patch by Stefan Miklosovic; reviewed by TBD for CASSANDRA-21390

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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