Fix memory reservation starvation in sort-merge#20642
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xudong963 wants to merge 4 commits intoapache:mainfrom
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Fix memory reservation starvation in sort-merge#20642xudong963 wants to merge 4 commits intoapache:mainfrom
xudong963 wants to merge 4 commits intoapache:mainfrom
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Update: I added an end-to-end test which fails on main |
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| // Transfer the pre-reserved merge memory to the streaming merge | ||
| // using `take()` instead of `new_empty()`. This ensures the merge | ||
| // stream starts with `sort_spill_reservation_bytes` already | ||
| // allocated, preventing starvation when concurrent sort partitions | ||
| // compete for pool memory. `take()` moves the bytes atomically | ||
| // without releasing them back to the pool, so other partitions | ||
| // cannot race to consume the freed memory. |
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The pre reserved merge memory should be used as part of the sort merge stream.
I mean that if x pre reserved merge memory was reserved the sort merge stream should know about that so it wont think it starting from 0, otherwise this just reserve for unaccounted memory
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Thanks! Good point — just take() alone wouldn't be enough if the merge stream doesn't know about the pre-reserved bytes.
The PR does address this in the other changed files:
- In builder.rs: BatchBuilder now tracks batches_mem_used separately and only calls try_grow() when actual usage exceeds the current reservation size. It also records initial_reservation so
it never shrinks below that during build_output. This way the pre-reserved bytes are used as the initial budget rather than requesting from the pool on top of them. - In multi_level_merge.rs: get_sorted_spill_files_to_merge now tracks total_needed and only requests additional pool memory when total_needed > reservation.size(), so spill file buffers
covered by the pre-reserved bytes don't trigger extra pool allocations.
So the merge stream is aware of the pre-reserved bytes and uses them as its starting budget — it doesn't think it's starting from 0.
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DataFusion 52.1.0 has a TOCTOU race in ExternalSorter where merge reservations are freed and re-created empty, letting other partitions steal the memory (apache/datafusion#20642). Until the upstream fix lands, compute a data-aware sort_spill_reservation_bytes by sampling actual Arrow row sizes from the input, estimating spill file count, and reserving enough for the merge phase.
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* Sample-based sort spill reservation to mitigate merge OOM DataFusion 52.1.0 has a TOCTOU race in ExternalSorter where merge reservations are freed and re-created empty, letting other partitions steal the memory (apache/datafusion#20642). Until the upstream fix lands, compute a data-aware sort_spill_reservation_bytes by sampling actual Arrow row sizes from the input, estimating spill file count, and reserving enough for the merge phase. * Add more tests * formatting * Allow some truncation here * Handle when budgets are tight * Better estimate in-memory size using row count and avg row size * Remove dead code * Lint fix * linting * Fix low memory situations
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Which issue does this PR close?
Rationale for this change
This PR fixes memory reservation starvation in sort-merge when multiple sort partitions share a GreedyMemoryPool.
When multiple
ExternalSorterinstances run concurrently and share a single memory pool, the merge phase starves:What changes are included in this PR?
Are these changes tested?
I can't find a deterministic way to reproduce the bug, but it occurs in our production.Add an end-to-end test to verify the fixAre there any user-facing changes?