perf: cache serialized query plans to avoid per-partition serialization #3246
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Replace ByteArrayOutputStream with direct CodedOutputStream serialization to eliminate unnecessary allocations during query plan serialization. This optimization: - Pre-allocates exact buffer size using getSerializedSize() - Eliminates ByteArrayOutputStream's internal buffer resizing - Removes defensive array copying from toByteArray() - Applies to 5 hot paths called per-partition during query execution For a query with 1000 partitions, this eliminates 5000+ unnecessary allocations and array copies, significantly reducing GC pressure. Changes: - operators.scala: getCometIterator() and convertBlock() - CometNativeWriteExec.scala: serializedPlanOpt() and doExecute() - ParquetFilters.scala: createNativeFilters()
Add caching for serialized protobuf query plans to avoid serializing the same plan repeatedly for every partition in CometExecIterator. Changes: - Add serializeNativePlan() helper method in CometExec - Add getCometIterator() overload accepting pre-serialized bytes - Update CometExecUtils.getNativeLimitRDD to serialize once - Update CometTakeOrderedAndProjectExec to serialize plans once For a query with N partitions, this eliminates N-1 redundant protobuf serializations per affected code path, reducing CPU overhead and GC pressure during query execution. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #3246 +/- ##
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+ Coverage 56.12% 60.11% +3.98%
- Complexity 976 1428 +452
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Files 119 170 +51
Lines 11743 15799 +4056
Branches 2251 2604 +353
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+ Hits 6591 9497 +2906
- Misses 4012 4983 +971
- Partials 1140 1319 +179 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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hsiang-c
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Jan 23, 2026
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Moving serialization out of mapPartitionsWithIndexInternal LGTM
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Which issue does this PR close?
N/A - Performance optimization
Rationale for this change
The
CometExec.getCometIterator()method serializes the protobuf query plan to bytes every time it's called. Since this method is called insidemapPartitions*for each partition, the same plan was being serialized N times for a query with N partitions. This causes unnecessary CPU overhead and GC pressure.What changes are included in this PR?
operators.scala - Added caching infrastructure:
serializeNativePlan(nativePlan: Operator): Array[Byte]- helper to serialize a plan oncegetCometIteratoroverload accepting pre-serializedArray[Byte]instead ofOperatorCometExecUtils.scala - Updated
getNativeLimitRDD:mapPartitionsWithIndexInternalCometTakeOrderedAndProjectExec.scala - Updated
doExecuteColumnar():How are these changes tested?
Existing tests pass:
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