Optimize delta binary decoder in the case where bitwidth=0#9477
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etseidl wants to merge 12 commits intoapache:mainfrom
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Optimize delta binary decoder in the case where bitwidth=0#9477etseidl wants to merge 12 commits intoapache:mainfrom
etseidl wants to merge 12 commits intoapache:mainfrom
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Not seeing the huge improvement from arrow-cpp, but still a nice speedup, and it doesn't seem to be impacting cases where the optimization can't be used. New benchmarks on my workstation (x86 i7-12700K) comparing main (no_opt) to this branch (opt) And the rest of the binary packed benches Details |
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Currently unknown what impact this optimization will have on the other delta encodings. There could be a good speedup for situations like constant length strings + DELTA_LENGTH_BYTE_ARRAY (think UUIDs or hashes), as well as long runs of the same prefix or long runs of strings with no shared prefix with DELTA_BYTE_ARRAY. |
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Pull request overview
This PR optimizes DELTA_BINARY_PACKED decoding for the common case where a miniblock has bit_width == 0, aiming to match speedups observed in Arrow C++ and address issue #9476.
Changes:
- Add a fast-path in the delta binary packed decoder for
bit_width == 0miniblocks (including constant-value and arithmetic-progression cases). - Add larger regression tests covering constant, increasing, and mixed patterns for
Int32/Int64. - Add new benchmark cases targeting constant and monotonically increasing delta-encoded pages.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
parquet/src/encodings/decoding.rs |
Adds bit_width == 0 decoding fast-path and new large tests for delta decoding correctness. |
parquet/benches/arrow_reader.rs |
Adds a page generator and benchmark cases for delta binary packed constant/increasing patterns. |
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Dandandan
reviewed
Feb 28, 2026
parquet/src/encodings/decoding.rs
Outdated
| if bit_width == 0 { | ||
| let min_delta = self.min_delta.as_i64()?; | ||
| if min_delta == 0 { | ||
| for v in &mut buffer[read..read + batch_read] { |
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this can use .fill() (if not faster, at least looks nice)
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I had done that, but on my laptop it was actually slower for some reason...I'll check again on a more modern processor. I do agree it would look nicer.
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Ok, on my workstation fill is a bit faster. On my laptop it's a bit slower. I'll go with the workstation results 😁
Dandandan
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Feb 28, 2026
| // Kudos to @pitrou for the idea https://github.com/apache/arrow/pull/49296 | ||
| if bit_width == 0 { | ||
| let min_delta = self.min_delta.as_i64()?; | ||
| if min_delta == 0 { |
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Can we repeat the min_delta==0 optimization below as well for bit_width > 0 ?
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I can try. The theory, however, is that the speed up is from not having to use the previous value to calculate the current. I'll see if there's any speedup from avoiding the additional wrapping_add.
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Done. It's good for 5-10% on my laptop.
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I think the code looks good! Lefr 2 comments |
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run benchmark arrow_reader |
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🤖 |
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🤖: Benchmark completed Details
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Dandandan
reviewed
Mar 2, 2026
| assert_eq!(count, EXPECTED_VALUE_COUNT); | ||
| }); | ||
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| // binary packed same value |
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Can you submit a PR for just these benchmarks, so we can run the benchmarks on this PR?
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I do have a separate branch for the benches (and will submit separately), but combined them in this draft. I'd like to do some tests with the other delta encodings to see if the optimization here has an impact.
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Sampling from the latest bench against #9500. The 'stepped' benches trigger the optimization suggested by @Dandandan (#9477 (comment)). The |
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Which issue does this PR close?
Rationale for this change
Explore if we can achieve the speedups seen in arrow-cpp (apache/arrow#49296).
What changes are included in this PR?
Adds special cases to the delta binary packed decoder when bitwidth for a miniblock is 0. The optimization avoids relying on previous values to decode current ones.
Are these changes tested?
Yes, tests have been added, as well as new benchmarks.
Are there any user-facing changes?
No