perf: stack-allocate decode buffers in tp_decompress_block#253
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perf: stack-allocate decode buffers in tp_decompress_block#253
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Replace palloc/pfree of two temporary uint32 arrays (doc_deltas, frequencies) with fixed-size stack arrays of TP_BLOCK_SIZE (128) elements. These 512-byte arrays (1 KiB total) are allocated on every block decompression call, and since TP_BLOCK_SIZE is a compile-time constant, they are safe VLA-free stack allocations. Eliminates allocator overhead on the hot path where profiling shows tp_decompress_block at 6.5% of CPU.
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Benchmark Results — MS-MARCO v2 (138M passages, 691 queries, LIMIT 10)Back-to-back runs on the same machine (16 cores, 123 GB RAM, PG17), identical query set. Per-Bucket Latency (p50 ms)
Summary
Modest end-to-end improvement as expected — |
tjgreen42
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Mar 3, 2026
## Summary - Update comparison page with results from benchmark run [22642807624](https://github.com/timescale/pg_textsearch/actions/runs/22642807624) - Overall throughput improved from 2.8x to 3.2x faster than System X - Build time gap narrowed from 2.0x to 1.6x (270s → 234s) - Key improvements since Feb 9: SIMD bitpack decoding (#250), stack-allocated decode buffers (#253), BMW term state pointer indirection (#249), arena allocator rewrite (#231), leader-only merge (#244) ## Testing - Numbers extracted from benchmark run on commit 1b09cc9 - gh-pages branch also needs updating (will push after merge)
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Summary
palloc/pfreeof two temporaryuint32arrays (doc_deltas,frequencies) intp_decompress_blockwith fixed-size stack arrays ofTP_BLOCK_SIZE(128) elementsTP_BLOCK_SIZEis a#defineconstant, so these are NOT VLAsTest plan
make clean && makecompiles with zero new warningsmake installcheck)make format-checkpasses