weaselbot
321a23f1dc
For point writes and point reads (end.len == 0), end.p is not part of the API contract and callers may leave it uninitialized -- both the C and C++ API smoke tests and the fuzz test driver do so. However, insertPointWritesOrSorted and check::Job::init unconditionally built a TrivialSpan from end.p, reading the uninitialized pointer even though it is never used for point operations. Move the end span construction into the range-write/range-read branches so end.p is only read when end.len > 0. This is semantically identical but removes the uninitialized reads that MemorySanitizer reports.
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 20.0.0 (++20241120082228+86734c857724-1~exp1~20241120202359.554)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-20/bin
Microbenchmark
Skip list
| ns/op | op/s | err% | ins/op | cyc/op | IPC | bra/op | miss% | total | benchmark |
|---|---|---|---|---|---|---|---|---|---|
| 161.29 | 6,200,056.17 | 0.1% | 3,014.03 | 831.04 | 3.627 | 504.59 | 0.0% | 1.93 | point reads |
| 158.32 | 6,316,160.64 | 0.1% | 2,954.16 | 815.80 | 3.621 | 490.17 | 0.0% | 1.89 | prefix reads |
| 237.39 | 4,212,409.50 | 0.2% | 3,592.41 | 1,233.96 | 2.911 | 629.31 | 0.0% | 2.84 | range reads |
| 442.11 | 2,261,878.94 | 0.0% | 4,450.57 | 2,314.25 | 1.923 | 707.92 | 2.1% | 5.28 | point writes |
| 439.89 | 2,273,308.53 | 0.1% | 4,410.22 | 2,302.29 | 1.916 | 694.74 | 2.1% | 5.25 | prefix writes |
| 290.96 | 3,436,936.78 | 0.0% | 2,315.38 | 1,528.68 | 1.515 | 396.69 | 3.3% | 3.49 | range writes |
| 476.93 | 2,096,762.02 | 0.6% | 6,999.33 | 2,484.94 | 2.817 | 1,251.73 | 1.3% | 0.06 | monotonic increasing point writes |
| 131,736.57 | 7,590.91 | 1.1% | 807,444.50 | 704,941.71 | 1.145 | 144,584.60 | 0.9% | 0.01 | worst case for radix tree |
| 45.50 | 21,978,369.95 | 1.1% | 902.00 | 232.36 | 3.882 | 132.00 | 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 |
|---|---|---|---|---|---|---|---|---|---|
| 12.36 | 80,885,626.43 | 0.2% | 243.56 | 63.62 | 3.828 | 31.07 | 0.6% | 0.15 | point reads |
| 14.18 | 70,502,196.81 | 0.1% | 297.72 | 73.13 | 4.071 | 40.31 | 0.5% | 0.17 | prefix reads |
| 33.44 | 29,901,623.04 | 0.1% | 767.90 | 172.42 | 4.454 | 101.32 | 0.2% | 0.40 | range reads |
| 19.48 | 51,342,564.70 | 0.3% | 374.45 | 100.43 | 3.728 | 48.92 | 0.5% | 0.23 | point writes |
| 37.46 | 26,694,471.44 | 0.1% | 672.00 | 193.14 | 3.479 | 101.28 | 0.3% | 0.45 | prefix writes |
| 38.78 | 25,784,784.34 | 0.0% | 738.26 | 199.93 | 3.693 | 111.59 | 0.1% | 0.47 | range writes |
| 76.05 | 13,148,995.74 | 0.7% | 1,450.77 | 397.16 | 3.653 | 275.72 | 0.0% | 0.01 | monotonic increasing point writes |
| 286,920.33 | 3,485.29 | 0.4% | 4,117,948.00 | 1,521,352.00 | 2.707 | 714,833.00 | 0.1% | 0.01 | worst case for radix tree |
| 95.66 | 10,453,798.72 | 0.5% | 1,986.00 | 495.04 | 4.012 | 315.00 | 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: 4.53508 seconds, 371.81 MB/s, Add: 3.81222 seconds, 150.919 MB/s, Gc ratio: 33.66%, Peak idle memory: 5.61007e+06
radix tree
Check: 0.957735 seconds, 1760.6 MB/s, Add: 1.19942 seconds, 479.678 MB/s, Gc ratio: 38.6069%, Peak idle memory: 2.05667e+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: 0.804598 seconds, 2095.69 MB/s, Add: 0.671221 seconds, 857.147 MB/s, Gc ratio: 35.0034%, Peak idle memory: 0