chore[btrblocks]: more precise FoR expected_compression_ratio#6301
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joseph-isaacs wants to merge 2 commits intodevelopfrom
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chore[btrblocks]: more precise FoR expected_compression_ratio#6301joseph-isaacs wants to merge 2 commits intodevelopfrom
FoR expected_compression_ratio#6301joseph-isaacs wants to merge 2 commits intodevelopfrom
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Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>
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Benchmarks: FineWeb NVMeSummary
Detailed Results Table
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Benchmarks: TPC-H SF=1 on NVMESummary
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Benchmarks: TPC-H SF=1 on S3Summary
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Benchmarks: TPC-DS SF=1 on NVMESummary
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Benchmarks: FineWeb S3Summary
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Benchmarks: TPC-H SF=10 on NVMESummary
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Benchmarks: Statistical and Population GeneticsSummary
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Benchmarks: TPC-H SF=10 on S3Summary
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Benchmarks: Clickbench on NVMESummary
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Benchmarks: Random AccessSummary
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a10y
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Feb 4, 2026
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Benchmarks: CompressionSummary
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Merging this PR will degrade performance by 33.73%
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robert3005
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Feb 6, 2026
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⏺ Here's the full picture:
Encoding Tree Diff Summary
The change eliminates 2,170 FoR wrappers where FoR doesn't reduce bit width
(e.g., l_partkey min=2 still needs 18 bits, l_suppkey min=1 still needs 14
bits). That part is correct.
But it introduces 185 new patches. The key example is the RunEnd ends column:
patches=None) — subtracting min=6 makes max=131066 fit in 17 bits
needs 18 bits, so value 131072 becomes a patch
The FoR estimation now considers these cases not worth it, but removing FoR
forces the bitpacked encoding to use patches for edge-case values. Patch
handling during decompression is the likely cause of the +46% decompress
regression.
The fix would be to make the FoR estimator account for cases where subtracting
the minimum reduces the bit width (i.e., where (max - min).ilog2() <
max.ilog2()). Those cases should still strongly prefer FoR.