refactor: Share left-side spill file across partitions on OOM fallback#21699
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viirya merged 1 commit intoapache:mainfrom Apr 19, 2026
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refactor: Share left-side spill file across partitions on OOM fallback#21699viirya merged 1 commit intoapache:mainfrom
viirya merged 1 commit intoapache:mainfrom
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| 01)ProjectionExec: expr=[count(Int64(1))@0 as count(*)], metrics=[<slt:ignore>] | ||
| 02)--AggregateExec: mode=Single, gby=[], aggr=[count(Int64(1))], metrics=[<slt:ignore>] | ||
| 03)----NestedLoopJoinExec: join_type=Inner, filter=v1@0 + v2@1 > 0, projection=[], metrics=[output_rows=100.0 K, <slt:ignore> spill_count=1, <slt:ignore>] | ||
| 03)----NestedLoopJoinExec: join_type=Inner, filter=v1@0 + v2@1 > 0, projection=[], metrics=[output_rows=100.0 K, <slt:ignore> spill_count=2, <slt:ignore>] |
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Now the left side spills during OOM, so spill_count increases from 1 to 2.
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LGTM, thank you!
One potential improvement is to let all partitions share the same buffered left-side chunk. This would allow us to process more left-side data per right-side probe pass under the same memory budget, reducing the number of probe passes.
This likely requires replacing the existing OnceAsync with a different coordination mechanism.
That said, the current solution is a good starting point, since spill encoding and decoding are relatively lightweight, we can iterate on this in the future.
Previously when OnceFut failed with OOM, each partition independently re-executed the left child to get its own stream. This was redundant since all partitions need the same left data. Now the first partition to initiate fallback spills the entire left side to disk via a shared OnceAsync<LeftSpillData>. Other partitions wait on the same future and read from the shared spill file, avoiding redundant re-execution of the left child. Co-authored-by: Claude Code
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apache#21699) ## Which issue does this PR close? <!-- We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. For example `Closes apache#123` indicates that this PR will close issue apache#123. --> - Closes #. ## Rationale for this change To reduce the redundant re-execution of the left side during OOM fallback. ## What changes are included in this PR? Previously when OnceFut failed with OOM, each partition independently re-executed the left child to get its own stream. This was redundant since all partitions need the same left data. Now the first partition to initiate fallback spills the entire left side to disk via a shared OnceAsync<LeftSpillData>. Other partitions wait on the same future and read from the shared spill file, avoiding redundant re-execution of the left child. Co-authored-by: Claude Code ## Are these changes tested? <!-- We typically require tests for all PRs in order to: 1. Prevent the code from being accidentally broken by subsequent changes 2. Serve as another way to document the expected behavior of the code If tests are not included in your PR, please explain why (for example, are they covered by existing tests)? --> Unit test ## Are there any user-facing changes? No <!-- If there are user-facing changes then we may require documentation to be updated before approving the PR. --> <!-- If there are any breaking changes to public APIs, please add the `api change` label. -->
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Which issue does this PR close?
Rationale for this change
To reduce the redundant re-execution of the left side during OOM fallback.
What changes are included in this PR?
Previously when OnceFut failed with OOM, each partition independently re-executed the left child to get its own stream. This was redundant since all partitions need the same left data.
Now the first partition to initiate fallback spills the entire left side to disk via a shared OnceAsync. Other partitions wait on the same future and read from the shared spill file, avoiding redundant re-execution of the left child.
Co-authored-by: Claude Code
Are these changes tested?
Unit test
Are there any user-facing changes?
No