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When USE_64_BIT=1, InternalVersionT stores an int64_t, but the aarch64 NEON fast paths in scan16 (both the indexed Node48 variant and the Node256 variant) and checkMaxBetweenExclusiveImpl(Node16) only copied the low 32 bits of each version into uint32x4_t lanes and compared against a truncated 32-bit readVersion. This produced wrong conflict/commit decisions once any version exceeded 2^32 - 1. Extract the per-version "greater than readVersion" computation into a shared conflictMask16 helper. For 64-bit versions it uses vcgtq_s64 on the full int64 values and narrows the resulting 16-byte mask into the same nibble-packed layout the callers already consume. The 32-bit path is preserved unchanged. Closes #69
A data structure for optimistic concurrency control on ranges of bitwise-lexicographically-ordered keys.
Intended as an alternative to FoundationDB's skip list.
Hardware for all benchmarks is an AMD Ryzen 9 7900 with (2x32GB) 5600MT/s CL28-34-34-89 1.35V RAM.
$ clang++ --version
Ubuntu clang version 21.1.8 (6ubuntu1)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-21/bin
Microbenchmark
Skip list
| ns/op | op/s | err% | ins/op | cyc/op | IPC | bra/op | miss% | total | benchmark |
|---|---|---|---|---|---|---|---|---|---|
| 164.29 | 6,086,873.38 | 0.0% | 3,107.03 | 604.19 | 5.142 | 558.59 | 0.0% | 1.96 | point reads |
| 161.05 | 6,209,395.38 | 0.1% | 3,036.76 | 592.21 | 5.128 | 539.35 | 0.0% | 1.93 | prefix reads |
| 239.55 | 4,174,539.38 | 0.1% | 3,722.71 | 880.68 | 4.227 | 692.00 | 0.0% | 2.86 | range reads |
| 354.75 | 2,818,919.14 | 0.7% | 4,523.64 | 1,304.75 | 3.467 | 720.22 | 2.0% | 4.23 | point writes |
| 345.32 | 2,895,878.47 | 0.1% | 4,484.57 | 1,270.31 | 3.530 | 705.00 | 1.8% | 4.12 | prefix writes |
| 193.48 | 5,168,547.42 | 0.1% | 2,224.10 | 711.72 | 3.125 | 377.17 | 3.3% | 2.32 | range writes |
| 404.89 | 2,469,777.50 | 2.4% | 6,855.96 | 1,489.70 | 4.602 | 1,227.82 | 1.3% | 0.05 | monotonic increasing point writes |
| 134,231.80 | 7,449.80 | 1.9% | 812,045.25 | 495,770.40 | 1.638 | 151,246.50 | 0.9% | 0.01 | worst case for radix tree |
| 37.80 | 26,454,311.17 | 0.4% | 701.00 | 139.14 | 5.038 | 102.00 | 0.0% | 0.01 | create and destroy |
Radix tree (this implementation)
| ns/op | op/s | err% | ins/op | cyc/op | IPC | bra/op | miss% | total | benchmark |
|---|---|---|---|---|---|---|---|---|---|
| 12.89 | 77,565,115.56 | 0.1% | 244.55 | 47.43 | 5.155 | 34.21 | 0.6% | 0.15 | point reads |
| 15.11 | 66,162,047.76 | 0.1% | 297.79 | 55.60 | 5.356 | 43.23 | 0.4% | 0.18 | prefix reads |
| 36.29 | 27,559,358.29 | 0.1% | 783.16 | 133.44 | 5.869 | 109.52 | 0.2% | 0.43 | range reads |
| 20.53 | 48,719,405.55 | 0.1% | 381.81 | 75.51 | 5.057 | 51.04 | 0.5% | 0.25 | point writes |
| 39.37 | 25,402,042.40 | 0.1% | 685.00 | 144.83 | 4.730 | 106.72 | 0.3% | 0.47 | prefix writes |
| 43.78 | 22,843,841.63 | 0.1% | 800.40 | 161.06 | 4.970 | 127.36 | 0.1% | 0.53 | range writes |
| 78.37 | 12,760,008.75 | 1.0% | 1,452.61 | 288.24 | 5.040 | 278.69 | 0.1% | 0.01 | monotonic increasing point writes |
| 322,885.50 | 3,097.07 | 1.5% | 4,362,382.00 | 1,183,852.00 | 3.685 | 765,301.00 | 0.1% | 0.01 | worst case for radix tree |
| 99.99 | 10,000,718.79 | 0.4% | 1,775.00 | 367.93 | 4.824 | 288.00 | 0.0% | 0.01 | create and destroy |
"Real data" test
Point queries only. Gc ratio is the ratio of time spent doing garbage collection to time spent adding writes or doing garbage collection. Lower is better.
skip list
Check: 4.62967 seconds, 352.195 MB/s, Add: 3.34177 seconds, 167.771 MB/s, Gc ratio: 37.9399%, Peak idle memory: 5.51852e+06
radix tree
Check: 1.00477 seconds, 1622.8 MB/s, Add: 1.21142 seconds, 462.808 MB/s, Gc ratio: 39.4716%, Peak idle memory: 2.0226e+06
hash table
(The hash table implementation doesn't work on range queries, and its purpose is to provide an idea of how fast point queries can be)
Check: 0.854254 seconds, 1908.74 MB/s, Add: 0.632626 seconds, 886.232 MB/s, Gc ratio: 41.0827%, Peak idle memory: 0