Dandandan opened a new pull request, #23202: URL: https://github.com/apache/datafusion/pull/23202
## Rationale for this change When a sort exceeds `sort_in_place_threshold_bytes`, `ExternalSorter` sorts each buffered batch individually and merges them all. With many small input batches this gives a very high merge fan-in (hundreds/thousands of one-batch runs). For single-column sorts the per-stream cursor/merge overhead dominates, making this much slower than sorting a few larger runs. ## What changes are included in this PR? For **single-column** sorts, coalesce the buffered batches into a small number of larger runs (each bounded by `sort_in_place_threshold_bytes`, the same limit the in-place concat path already uses) before sorting and merging. Multi-column keys are left unchanged — their row-format merge of many small sorted runs beats a few large lexicographic sorts. Coalescing is disabled on the (memory-constrained) spill path. `benches/sort.rs`: single-column cases **1.4×–2.4× faster** (i64/f64 ~2×, utf8/utf8view ~1.6–1.9×, dictionary up to 2.4×) at 100k and 1M rows; multi-column cases unchanged. ## Are these changes tested? Yes — existing `sorts::` tests pass, plus a new `test_in_mem_sort_coalesced_runs` verifying the coalesced multi-run merge produces a correct total order (incl. NULLs). ## Are there any user-facing changes? No (internal performance change only). -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
