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strinc() in ConflictSet.cpp used std::string_view::size() (size_t) and subtracted 1 without first checking for an empty string. For the root node, getSearchPath() returns the empty string, so every debug correctness check underflowed size_t and relied on implementation-defined conversion to signed int. prefixRange() in Bench.cpp had the same loop shape. Although TrivialSpan::size() returns int, on an empty (or all-0xff) key the function then asserted and continued executing, allocating a zero-length buffer and writing before its start. Changes: - In strinc(), initialize index as signed int(str.size()) - 1 so the loop is skipped for empty input, and return ok=false cleanly. - In prefixRange(), initialize index the same way and call std::abort() after the assert so invalid input cannot fall through to an out-of-bounds write. - Replace C-style uint8_t casts with explicit static_casts. Closes #59
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