perf: use stdlib bisect and attrgetter in tablets.py (100's of ns, 1.5-5.6x speedup)#757
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According to our README, we support Python 3.10-3.14 right now, so it should be fine to drop the pure-python impl and use the builtin one instead. |
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- Use bisect.bisect_left from stdlib unconditionally (C implementation); drop the bundled pure-Python fallback since we only support Python 3.10+ - Replace per-call lambda closures with module-level operator.attrgetter for first_token/last_token extraction - Add unit tests for get_tablet_for_key Benchmark results (get_tablet_for_key hit): 10 tablets: 517 ns -> 365 ns (1.42x) 100 tablets: 616 ns -> 351 ns (1.75x) 1000 tablets: 1008 ns -> 529 ns (1.91x) 10000 tablets: 1339 ns -> 610 ns (2.20x)
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Maintain parallel _first_tokens and _last_tokens dicts alongside _tablets, each mapping (keyspace, table) to a plain list[int]. This lets bisect_left run entirely in C on native ints instead of calling an attrgetter callback on every comparison during binary search. Follow-up to PR scylladb#757 which identified the opportunity: its own benchmarks showed bisect_left without key= is 2.7-5.7x faster than with key=attrgetter. Results (best-of-5, Python 3.14): get_tablet_for_key (hit): Tablets Before After Saved Speedup 10 293ns 216ns 78ns 1.36x 100 351ns 233ns 118ns 1.51x 1,000 448ns 267ns 181ns 1.68x 10,000 537ns 282ns 255ns 1.90x All three dicts are kept in sync by add_tablet, drop_tablets, and drop_tablets_by_host_id. The attrgetter imports are no longer needed and have been removed.
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Maintain parallel _first_tokens and _last_tokens dicts alongside _tablets, each mapping (keyspace, table) to a plain list[int]. This lets bisect_left run entirely in C on native ints instead of calling an attrgetter callback on every comparison during binary search. Follow-up to PR scylladb#757 which identified the opportunity: its own benchmarks showed bisect_left without key= is 2.7-5.7x faster than with key=attrgetter. Results (best-of-5, Python 3.14): get_tablet_for_key (hit): Tablets Before After Saved Speedup 10 293ns 216ns 78ns 1.36x 100 351ns 233ns 118ns 1.51x 1,000 448ns 267ns 181ns 1.68x 10,000 537ns 282ns 255ns 1.90x All three dicts are kept in sync by add_tablet, drop_tablets, and drop_tablets_by_host_id. The attrgetter imports are no longer needed and have been removed.
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Summary
bisect.bisect_leftunconditionally (C implementation). Since we only support Python 3.10-3.14, drop the bundled pure-Python fallback entirely.operator.attrgetterforfirst_token/last_tokenextraction, avoiding repeated function-object allocation.get_tablet_for_key(3 tests).Benchmark Results
Measured on Intel i7-1270P, Python 3.14.3, CPU-pinned, 200k iterations.
get_tablet_for_key(hit — the primary hot path)bisect_leftwithkey=(isolated)bisect_leftwithoutkey=(plain ints)