optimize(parquet): Nested list batching child.write calls - #10085
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mapleFU
commented
Jun 6, 2026
| /// counting child-element starts to find and stamp slot boundaries. | ||
| /// | ||
| /// Scan backward because we don't know start offset before writing. | ||
| fn write_list_scan<O: OffsetSizeTrait>( |
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I previously want to remove the branch for write non-nested childs, however benchmark shows that adding a more branch will hurt the performance. So I split it to two functions.
| for rep in rep_levels.iter_mut().rev() { | ||
| // This can uses `==`, since list write is recursive and the child is written | ||
| // before the parent. | ||
| if *rep <= ctx.rep_level { |
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I still use <= because benchmark shows no performance enhancement between <= and ==, so just uses <=
| // before the parent. | ||
| if *rep <= ctx.rep_level { | ||
| seen += 1; | ||
| if seen == next_stamp_at { |
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Maybe we can SIMD this in the future, this is not cirtical in this branch. Or we can "batching" if list offsets is large. E.g. checking not one-by-one, and just batch by batch
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Pull request overview
This PR optimizes Parquet level generation for nested Arrow List types by batching child.write(...) calls and applying repetition-level backfilling in larger chunks, reducing recursive write-call overhead for deeply nested list structures.
Changes:
- Split list writing into two specialized hot paths: an offsets-based “direct” backfill for last-level list children and a backward-scan backfill for nested repetition cases
- Extracted a shared run-classification loop (
write_list_impl) to batch null/empty/non-empty runs while keeping monomorphized backfill strategies
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mapleFU
commented
Jun 6, 2026
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run benchmark arrow_writer |
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🤖 Arrow criterion benchmark running (GKE) | trigger CPU Details (lscpu)Comparing nested-list-optimize-write (0d16db7) to c3e0684 (merge-base) diff File an issue against this benchmark runner |
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🤖 Arrow criterion benchmark completed (GKE) | trigger Instance: CPU Details (lscpu)Details
Resource Usagebase (merge-base)
branch
File an issue against this benchmark runner |
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run benchmark arrow_writer |
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Hi @mapleFU, thanks for the request (#10085 (comment)). Only whitelisted users can trigger benchmarks. Allowed users: Dandandan, Fokko, Jefffrey, Omega359, Rachelint, adriangb, alamb, asubiotto, brunal, buraksenn, cetra3, codephage2020, coderfender, comphead, erenavsarogullari, etseidl, friendlymatthew, gabotechs, geoffreyclaude, grtlr, haohuaijin, jonathanc-n, kevinjqliu, klion26, kosiew, kumarUjjawal, kunalsinghdadhwal, liamzwbao, mbutrovich, mkleen, mzabaluev, neilconway, rluvaton, sdf-jkl, timsaucer, xudong963, zhuqi-lucas. File an issue against this benchmark runner |
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@alamb Can we retrigger the benchmarking? I cannot reproducing the regression on my local MacOS machine =_= |
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run benchmark arrow_writer |
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I think the benchmark has been somewhat sensitive recently (I think we have it going so fast it is now very sensitive to subtle changes in environment) |
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@HippoBaro do you have time to help review this PR? |
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🤖 Arrow criterion benchmark running (GKE) | trigger CPU Details (lscpu)Comparing nested-list-optimize-write (09c2b84) to 6035e28 (merge-base) diff File an issue against this benchmark runner |
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🤖 Arrow criterion benchmark completed (GKE) | trigger Instance: CPU Details (lscpu)Details
Resource Usagebase (merge-base)
branch
File an issue against this benchmark runner |
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Thank you @mapleFU for the PR 🙇 I'll review this tomorrow! |
HippoBaro
approved these changes
Jul 8, 2026
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| // `==` would also work here: the child is written before the | ||
| // parent, so no entry within the batch has rep < ctx.rep_level. | ||
| // Benchmarks show no difference, so keep the more defensive `<=`. |
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I think the invariant holds, but let's have
debug_assert!(*rep >= ctx.rep_level)here for good measure?
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Sorry for late reply, I'm so busy in these weeks, I've addressed the comments now |
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@alamb should we move this forward or this is blocked? |
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I don't think it is blocked, it just needs a review. I will try and find to do so |
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Oh, actually I see now that @HippoBaro already did. Awesome |
alamb
approved these changes
Jul 20, 2026
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I took another look and I think it also looks good to me -- thank you @HippoBaro and @mapleFU
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Which issue does this PR close?
Rationale for this change
Optimize nested list call recursive write counts.
What changes are included in this PR?
Separate list write function to direct-by-offsets and by backward scan
Are these changes tested?
Covered by existing
Are there any user-facing changes?
No