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Merge pull request #30 from hadashiA/optimize-key-digests
Add key digest arrays to BTree nodes (format 1.1)
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‎README.md‎

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@@ -7,7 +7,7 @@ DryDB is a read-only embedded B+Tree based key/value database, implemented pure
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<picture>
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<source media="(prefers-color-scheme: dark)" srcset="docs/benchmarks/point_lookup_dark.svg">
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<img alt="Point lookup benchmark: DryDB 25 ns, RocksDB 239 ns, SQLite (prepared + immutable) 709 ns, SQLite (default) 5,412 ns per query" src="docs/benchmarks/point_lookup_light.svg">
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<img alt="Point lookup benchmark: DryDB 18 ns, RocksDB 383 ns, SQLite (prepared + immutable) 761 ns, SQLite (default) 5,648 ns per query" src="docs/benchmarks/point_lookup_light.svg">
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See [Performance](#performance) for details.
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<picture>
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<source media="(prefers-color-scheme: dark)" srcset="docs/benchmarks/point_lookup_dark.svg">
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<img alt="Point lookup benchmark: DryDB 25 ns, RocksDB 239 ns, SQLite (prepared + immutable) 709 ns, SQLite (default) 5,412 ns per query" src="docs/benchmarks/point_lookup_light.svg">
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<img alt="Point lookup benchmark: DryDB 18 ns, RocksDB 383 ns, SQLite (prepared + immutable) 761 ns, SQLite (default) 5,648 ns per query" src="docs/benchmarks/point_lookup_light.svg">
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### Range scan
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<source media="(prefers-color-scheme: dark)" srcset="docs/benchmarks/range_scan_dark.svg">
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<img alt="Range scan benchmark (100 rows): DryDB 0.5 µs, SQLite (prepared + immutable) 6 µs, RocksDB 10.3 µs, SQLite (default) 10.5 µs per query" src="docs/benchmarks/range_scan_light.svg">
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<img alt="Range scan benchmark (100 rows): DryDB 0.7 µs, SQLite (prepared + immutable) 8 µs, RocksDB 13.1 µs, SQLite (default) 15 µs per query" src="docs/benchmarks/range_scan_light.svg">
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### Count by key range
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<details>
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<summary>Raw BenchmarkDotNet results</summary>
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1 op = 1000 queries for point lookup, 100 queries for range scan and count. The `Parallel` variants run 8 threads of 1000 queries each: `ParallelSpread` reads spread-out keys (the realistic shape), `Parallel` hammers a single key (worst case for page refcount contention). `RandomKeys` defeats the branch predictor with a pseudo-random key sequence. `OpenAndFirstRead` opens the database file and runs one query.
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| Type | Method | Mean | Error | StdDev | Allocated |
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|--------------- |------------------------------- |-------------:|-------------:|-----------:|-----------:|
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| ReadBenchmark | DryDB_FindByKey | 24.80 us | 2.017 us | 1.334 us | - |
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| ReadBenchmark | DryDB_FindByKeyAsync | 27.81 us | 0.591 us | 0.391 us | - |
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| ReadBenchmark | DryDB_FindByKey_RandomKeys | 43.37 us | 2.248 us | 1.176 us | - |
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| ReadBenchmark | DryDB_FindByKey_ParallelSpread | 213.66 us | 3.046 us | 1.812 us | 1550 B |
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| ReadBenchmark | DryDB_FindByKey_Parallel | 885.10 us | 20.434 us | 13.516 us | 1296 B |
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| ReadBenchmark | RocksDB_FindByKey | 239.35 us | 8.747 us | 5.205 us | 40032 B |
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| ReadBenchmark | CsSqlite_FindByKey_Fair | 708.89 us | 8.700 us | 4.550 us | 48000 B |
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| ReadBenchmark | CsSqlite_FindByKey | 5,412.34 us | 124.296 us | 73.967 us | 48000 B |
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| RangeBenchmark | DryDB_GetRange | 50.36 us | 3.490 us | 2.308 us | - |
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| RangeBenchmark | CsSqlite_GetRange_Fair | 597.25 us | 20.959 us | 13.863 us | 480000 B |
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| RangeBenchmark | RocksDB_GetRange | 1,026.97 us | 47.101 us | 28.029 us | 726432 B |
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| RangeBenchmark | CsSqlite_GetRange | 1,051.58 us | 35.486 us | 18.560 us | 480000 B |
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| CountBenchmark | DryDB_CountRange | 112.00 us | 2.285 us | 1.511 us | - |
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| CountBenchmark | CsSqlite_CountRange_Fair | 9,253.18 us | 352.778 us | 233.341 us | - |
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| CountBenchmark | CsSqlite_CountRange | 9,566.06 us | 204.066 us | 106.731 us | - |
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| CountBenchmark | RocksDB_CountRange | 63,871.91 us | 1,284.642 us | 849.711 us | 25606432 B |
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| OpenBenchmark | DryDB_OpenAndFirstRead | 133.34 us | 6.287 us | 3.741 us | 639292 B |
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Each benchmark class is measured in its own run. 1 op = 1000 queries for point lookup, 100 queries for range scan and count. The `Parallel` variants run 8 threads of 1000 queries each: `ParallelSpread` reads spread-out keys (the realistic shape), `Parallel` hammers a single key (worst case for page refcount contention). `RandomKeys` defeats the branch predictor with a pseudo-random key sequence. `OpenAndFirstRead` opens the database file and runs one query. The `1M` variants read a 1,000,000-row (~45 MB) table where the working set no longer fits in the CPU cache.
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| Type | Method | Mean | Error | StdDev | Allocated |
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|----------------- |------------------------------- |-------------:|-------------:|-------------:|-----------:|
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| ReadBenchmark | DryDB_FindByKey | 18.35 us | 0.155 us | 0.102 us | - |
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| ReadBenchmark | DryDB_FindByKeyAsync | 23.23 us | 0.181 us | 0.119 us | - |
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| ReadBenchmark | DryDB_FindByKey_RandomKeys | 33.75 us | 0.277 us | 0.165 us | - |
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| ReadBenchmark | DryDB_FindByKey_ParallelSpread | 231.72 us | 15.138 us | 10.013 us | 1549 B |
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| ReadBenchmark | DryDB_FindByKey_Parallel | 741.33 us | 13.685 us | 9.052 us | 1295 B |
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| ReadBenchmark | RocksDB_FindByKey | 382.77 us | 35.751 us | 23.647 us | 40032 B |
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| ReadBenchmark | CsSqlite_FindByKey_Fair | 761.17 us | 20.744 us | 10.850 us | 48000 B |
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| ReadBenchmark | CsSqlite_FindByKey | 5,648.13 us | 349.447 us | 231.138 us | 48000 B |
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| RangeBenchmark | DryDB_GetRange | 65.51 us | 8.840 us | 5.847 us | - |
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| RangeBenchmark | CsSqlite_GetRange_Fair | 801.38 us | 31.965 us | 16.719 us | 480000 B |
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| RangeBenchmark | RocksDB_GetRange | 1,308.55 us | 111.460 us | 73.724 us | 726432 B |
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| RangeBenchmark | CsSqlite_GetRange | 1,498.53 us | 105.935 us | 70.069 us | 480000 B |
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| CountBenchmark | DryDB_CountRange | 146.10 us | 11.450 us | 7.570 us | - |
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| CountBenchmark | CsSqlite_CountRange_Fair | 11,384.10 us | 170.490 us | 101.450 us | - |
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| CountBenchmark | CsSqlite_CountRange | 11,948.20 us | 382.170 us | 199.880 us | - |
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| CountBenchmark | RocksDB_CountRange | 79,329.60 us | 3,939.950 us | 2,606.030 us | 25606432 B |
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| OpenBenchmark | DryDB_OpenAndFirstRead | 178.00 us | 31.360 us | 20.740 us | 652769 B |
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| BigReadBenchmark | DryDB_FindByKey_1M | 53.91 us | 0.185 us | 0.122 us | - |
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| BigReadBenchmark | DryDB_FindByKey_1M_RandomKeys | 87.72 us | 1.339 us | 0.886 us | - |
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| BigReadBenchmark | DryDB_GetRange_1M | 47.78 us | 0.065 us | 0.039 us | - |
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</details>
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‎docs/benchmarks/count_range_dark.svg‎

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‎docs/benchmarks/count_range_light.svg‎

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‎docs/benchmarks/point_lookup_dark.svg‎

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‎docs/benchmarks/point_lookup_light.svg‎

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