perf: Optimize ExternalSorter with chunked sort pipeline and radix sort kernel#21600
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mbutrovich wants to merge 26 commits intoapache:mainfrom
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perf: Optimize ExternalSorter with chunked sort pipeline and radix sort kernel#21600mbutrovich wants to merge 26 commits intoapache:mainfrom
mbutrovich wants to merge 26 commits intoapache:mainfrom
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…to choose between sort implementations.
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| } else if self.sorted_runs_memory > reservation_size { | ||
| self.reservation | ||
| .grow(self.sorted_runs_memory - reservation_size); | ||
| } |
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The comment says it would only exceed the limit by a small amount, but wouldn't this compound across partitions if it's a high amount of them?
Maybe we could still use a try grow here and remedy the failure, or at least cap the grow amount?
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I updated the comments to explain the scenario a bit more, but let me know if you still think we should do something more strict.
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| let use_radix_for_this_batch = | ||
| self.use_radix && batch.num_rows() > self.batch_size; | ||
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nit: since there is already a gate in sort_batch that handles radix vs lexsort maybe we could change the name of this variable for readability to something like use_chunked_radix?
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also just realizing, the "graceful degradation" section says the pipeline falls back to lexsort below batch_size rows, but wouldn't the else branch here still take the radix path? When use_radix_for_this_batch is false, this calls sort_batch, and sort_batch independently checks use_radix_sort when fetch.is_none()
for radix-eligible schemas it takes the radix path regardless of row count. Wouldn't that be slower?
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Thanks for the feedback @gratus00! I addressed both of these. Checking per-batch is wasteful too. I created an inner function that we can call directly because sort_batch is a public API and I don't want to change it.
- Always coalesce to `sort_coalesce_target_rows` regardless of schema (removed conditional that fell back to `batch_size` for non-radix) - Both radix and lexsort paths now go through `sort_batch_chunked` (both chunk output to `batch_size`) - Per-batch radix decision uses `sort_coalesce_target_rows` as threshold instead of `batch_size` - Added `radix_sorted_batches` and `lexsort_sorted_batches` counters to `ExternalSorterMetrics` - Added `sort_coalesce_target_rows` and `sort_use_radix` config fields to `ExternalSorter` - New `sort_use_radix` parameter gates the `use_radix_sort()` schema check ## `datafusion/common/src/config.rs` - New config: `sort_use_radix: bool, default = true` - Updated `sort_coalesce_target_rows` doc ## `datafusion/execution/src/config.rs` - New builder method: `with_sort_use_radix()` ## `datafusion/core/tests/fuzz_cases/sort_fuzz.rs` - `(20000, false)` → `(50000, true)` to fix flaky test ## `datafusion/sqllogictest/test_files/information_schema.slt` + `docs/source/user-guide/configs.md` - Added `sort_use_radix` entry, updated `sort_coalesce_target_rows` description
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So this is showing the improvement afforded by both the ExternalSorter rewrite (which helps lexsort by reducing fan-in) and radix sorting. I will push a commit that defaults radix sort off, run the benchmarks again to get a baseline understanding of the ExternalSorter changes. |
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So it seems like the big win here is the ExternalSorter refactor reducing merge fan-in, considering this run has radix sort off and the speedup is still pretty strong. This PR is mostly for experimenting anyway, but maybe this is motivation to structure the future work as:
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…erge fan-in. Subset of changes from apache#21600.
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Draft for benchmarking, builds on #21525.
Which issue does this PR close?
Partially addresses #21543.
Rationale for this change
ExternalSorter's merge path sorts each incoming batch individually (typically 8192 rows), then k-way merges all of them. This creates two problems:
lexsort_to_indicesat 32K+ rows for multi-column sorts, but at 8K rows theRowConverterencoding cost dominates. TPC-H SF10 benchmarks on perf: Bring over apache/arrow-rs/9683 radix sort, integrate into ExternalSorter #21525 confirmed this: naively swapping in radix sort made 12/22 queries slower (up to 1.20x).What changes are included in this PR?
Chunked sort pipeline
Replaces ExternalSorter's buffer-then-sort architecture with a coalesce-then-sort pipeline:
BatchCoalesceruntilsort_coalesce_target_rows(default 32768) is reachedbatch_sizeStreamingMergeBuilderUniform coalescing, per-batch algorithm selection
All schemas coalesce to
sort_coalesce_target_rows. This reduces merge fan-in for all queries, including single-column sorts like sort-merge join keys.Per batch, radix sort is used when the schema is eligible (multi-column, primitives/strings) and the batch reached
sort_coalesce_target_rows. Otherwise lexsort is used. Asort_use_radixconfig (defaulttrue) allows disabling radix entirely to isolate the pipeline's contribution.Metrics
New
radix_sorted_batchesandlexsort_sorted_batchescounters inExternalSorterMetrics, visible inEXPLAIN ANALYZE.Dead code removal
Sorted runs no longer require an in-memory merge before spilling. Removes
in_mem_sort_stream,sort_batch_stream,consume_and_spill_append,spill_finish,organize_stringview_arrays, andin_progress_spill_file.Config changes
sort_coalesce_target_rows(default 32768)sort_use_radix(default true)sort_in_place_threshold_bytes(no longer read,warnattribute per API health policy)Are these changes tested?
information_schema.sltupdated for new configsAre there any user-facing changes?
sort_coalesce_target_rows(default 32768) controls coalesce targetsort_use_radix(default true) enables/disables radix sortradix_sorted_batchesandlexsort_sorted_batchesinEXPLAIN ANALYZEsort_in_place_threshold_bytesis deprecated