Vasyl Protsiv
138286f3b1
The `SumTree::append` method is slow when appending large trees to small trees. The reason is this code here: https://github.com/zed-industries/zed/blob/f57f4cd3607e8298ef5f1b29929df2db0185d826/crates/sum_tree/src/sum_tree.rs#L628-L630 `append` is called recursively until `self` and `other` have the same height, effectively making this code `O(log^2 n)` in the number of leaves of `other` tree in the worst case. There are no algorithmic reasons why appending large trees must be this much slower. This PR proves it by providing implementation of `append` that works in logarithmic time regardless if `self` is smaller or larger than `other`. The helper method `append_large` has the symmetric logic to `push_tree_recursive` but moves the (unlikely) case of merging underflowing node in a separate helper function to reduce stack usage. I am a bit unsure about some implementation choices made in `push_tree_recursive` and would like to discuss some of these later, but at the moment I didn't change anything there and tried to follow the same logic in `append_large`. We might also consider adding `push_front`/`prepend` methods to `SumTree`. I did not find a good benchmark that covers this case so I added a new one to rope benchmarks. <details> <summary>cargo bench (compared to current main)</summary> ``` Running benches\rope_benchmark.rs (D:\zed\target\release\deps\rope_benchmark-59c669d2895cd2c4.exe) Gnuplot not found, using plotters backend push/4096 time: [195.67 µs 195.75 µs 195.86 µs] thrpt: [19.944 MiB/s 19.955 MiB/s 19.964 MiB/s] change: time: [+0.2162% +0.3040% +0.4057%] (p = 0.00 < 0.05) thrpt: [-0.4040% -0.3030% -0.2157%] Change within noise threshold. Found 14 outliers among 100 measurements (14.00%) 2 (2.00%) low mild 6 (6.00%) high mild 6 (6.00%) high severe Benchmarking push/65536: Warming up for 3.0000 s Warning: Unable to complete 100 samples in 5.0s. You may wish to increase target time to 7.8s, enable flat sampling, or reduce sample count to 50. push/65536 time: [1.4431 ms 1.4485 ms 1.4546 ms] thrpt: [42.966 MiB/s 43.147 MiB/s 43.310 MiB/s] change: time: [-3.2257% -1.2013% +0.6431%] (p = 0.27 > 0.05) thrpt: [-0.6390% +1.2159% +3.3332%] No change in performance detected. Found 11 outliers among 100 measurements (11.00%) 1 (1.00%) low mild 5 (5.00%) high mild 5 (5.00%) high severe append/4096 time: [15.107 µs 15.128 µs 15.149 µs] thrpt: [257.86 MiB/s 258.22 MiB/s 258.58 MiB/s] change: time: [+0.9650% +1.5256% +1.9057%] (p = 0.00 < 0.05) thrpt: [-1.8701% -1.5026% -0.9557%] Change within noise threshold. Found 2 outliers among 100 measurements (2.00%) 1 (1.00%) low mild 1 (1.00%) high severe append/65536 time: [1.2870 µs 1.4496 µs 1.6484 µs] thrpt: [37.028 GiB/s 42.106 GiB/s 47.425 GiB/s] change: time: [-28.699% -16.073% -0.3133%] (p = 0.04 < 0.05) thrpt: [+0.3142% +19.151% +40.250%] Change within noise threshold. Found 17 outliers among 100 measurements (17.00%) 1 (1.00%) high mild 16 (16.00%) high severe slice/4096 time: [30.580 µs 30.611 µs 30.639 µs] thrpt: [127.49 MiB/s 127.61 MiB/s 127.74 MiB/s] change: time: [-2.2958% -0.9674% -0.1835%] (p = 0.08 > 0.05) thrpt: [+0.1838% +0.9769% +2.3498%] No change in performance detected. slice/65536 time: [614.86 µs 795.04 µs 1.0293 ms] thrpt: [60.723 MiB/s 78.613 MiB/s 101.65 MiB/s] change: time: [-12.714% +7.2092% +30.676%] (p = 0.52 > 0.05) thrpt: [-23.475% -6.7244% +14.566%] No change in performance detected. Found 14 outliers among 100 measurements (14.00%) 14 (14.00%) high severe bytes_in_range/4096 time: [3.3298 µs 3.3416 µs 3.3563 µs] thrpt: [1.1366 GiB/s 1.1416 GiB/s 1.1456 GiB/s] change: time: [+2.0652% +3.0667% +4.3765%] (p = 0.00 < 0.05) thrpt: [-4.1930% -2.9754% -2.0234%] Performance has regressed. Found 2 outliers among 100 measurements (2.00%) 2 (2.00%) high severe bytes_in_range/65536 time: [80.640 µs 80.825 µs 81.024 µs] thrpt: [771.38 MiB/s 773.28 MiB/s 775.05 MiB/s] change: time: [-0.6566% +1.0994% +2.9691%] (p = 0.27 > 0.05) thrpt: [-2.8835% -1.0875% +0.6609%] No change in performance detected. Found 10 outliers among 100 measurements (10.00%) 2 (2.00%) high mild 8 (8.00%) high severe chars/4096 time: [763.17 ns 763.68 ns 764.36 ns] thrpt: [4.9907 GiB/s 4.9952 GiB/s 4.9985 GiB/s] change: time: [-2.1138% -0.7973% +0.1096%] (p = 0.18 > 0.05) thrpt: [-0.1095% +0.8037% +2.1595%] No change in performance detected. Found 10 outliers among 100 measurements (10.00%) 1 (1.00%) low severe 6 (6.00%) low mild 3 (3.00%) high severe chars/65536 time: [12.479 µs 12.503 µs 12.529 µs] thrpt: [4.8714 GiB/s 4.8817 GiB/s 4.8910 GiB/s] change: time: [-2.4451% -1.0638% +0.6633%] (p = 0.16 > 0.05) thrpt: [-0.6589% +1.0753% +2.5063%] No change in performance detected. Found 11 outliers among 100 measurements (11.00%) 4 (4.00%) high mild 7 (7.00%) high severe clip_point/4096 time: [63.148 µs 63.182 µs 63.229 µs] thrpt: [61.779 MiB/s 61.825 MiB/s 61.859 MiB/s] change: time: [+1.0107% +2.1329% +4.2849%] (p = 0.02 < 0.05) thrpt: [-4.1088% -2.0883% -1.0006%] Performance has regressed. Found 5 outliers among 100 measurements (5.00%) 4 (4.00%) high mild 1 (1.00%) high severe Benchmarking clip_point/65536: Warming up for 3.0000 s Warning: Unable to complete 100 samples in 5.0s. You may wish to increase target time to 7.8s, enable flat sampling, or reduce sample count to 50. clip_point/65536 time: [1.2578 ms 1.2593 ms 1.2608 ms] thrpt: [49.573 MiB/s 49.631 MiB/s 49.690 MiB/s] change: time: [+0.4881% +0.8942% +1.3488%] (p = 0.00 < 0.05) thrpt: [-1.3308% -0.8863% -0.4857%] Change within noise threshold. Found 15 outliers among 100 measurements (15.00%) 1 (1.00%) high mild 14 (14.00%) high severe point_to_offset/4096 time: [16.211 µs 16.235 µs 16.257 µs] thrpt: [240.28 MiB/s 240.61 MiB/s 240.97 MiB/s] change: time: [-1.4913% +0.1685% +2.2662%] (p = 0.89 > 0.05) thrpt: [-2.2159% -0.1682% +1.5139%] No change in performance detected. Found 2 outliers among 100 measurements (2.00%) 1 (1.00%) high mild 1 (1.00%) high severe point_to_offset/65536 time: [360.06 µs 360.58 µs 361.16 µs] thrpt: [173.05 MiB/s 173.33 MiB/s 173.58 MiB/s] change: time: [+0.0939% +0.8792% +1.8751%] (p = 0.06 > 0.05) thrpt: [-1.8406% -0.8715% -0.0938%] No change in performance detected. Found 10 outliers among 100 measurements (10.00%) 3 (3.00%) high mild 7 (7.00%) high severe cursor/4096 time: [19.266 µs 19.282 µs 19.302 µs] thrpt: [202.38 MiB/s 202.58 MiB/s 202.75 MiB/s] change: time: [+1.2457% +2.2477% +2.8702%] (p = 0.00 < 0.05) thrpt: [-2.7901% -2.1983% -1.2304%] Performance has regressed. Found 4 outliers among 100 measurements (4.00%) 2 (2.00%) high mild 2 (2.00%) high severe cursor/65536 time: [467.63 µs 468.36 µs 469.14 µs] thrpt: [133.22 MiB/s 133.44 MiB/s 133.65 MiB/s] change: time: [-0.2019% +1.3419% +2.8915%] (p = 0.10 > 0.05) thrpt: [-2.8103% -1.3241% +0.2023%] No change in performance detected. Found 12 outliers among 100 measurements (12.00%) 3 (3.00%) high mild 9 (9.00%) high severe append many/small to large time: [37.419 ms 37.656 ms 37.929 ms] thrpt: [321.84 MiB/s 324.17 MiB/s 326.22 MiB/s] change: time: [+0.8113% +1.7361% +2.6538%] (p = 0.00 < 0.05) thrpt: [-2.5852% -1.7065% -0.8047%] Change within noise threshold. Found 9 outliers among 100 measurements (9.00%) 9 (9.00%) high severe append many/large to small time: [51.289 ms 51.437 ms 51.614 ms] thrpt: [236.50 MiB/s 237.32 MiB/s 238.00 MiB/s] change: time: [-87.518% -87.479% -87.438%] (p = 0.00 < 0.05) thrpt: [+696.08% +698.66% +701.13%] Performance has improved. Found 13 outliers among 100 measurements (13.00%) 4 (4.00%) high mild 9 (9.00%) high severe ``` </details> Release Notes: - sum_tree: Make SumTree::append run in logarithmic time
Zed
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