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8266431: Dual-Pivot Quicksort improvements (Radix sort) #27411

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VladimirIaroslavski
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@VladimirIaroslavski VladimirIaroslavski commented Sep 21, 2025 •
edited by openjdk bot
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The goal of the PR is to improve both, sequential and parallel, sorting of primitives.

The main achievements

  • introduced Radix in parallel sorting which shows several times boost of performance and has linear complexity instead of n*ln(n)

  • improved mixed insertion sort (makes whole sorting faster)

  • improved merging sort for almost sorted data

  • optimized parallel sorting

  • improved step for pivot candidates and pivot partitioning

  • suggested better buffer allocation: if no memory, it is switched to in-place sorting with no OutOfMemoryError

  • minor javadoc and comment changes

  • extended existing tests

  • added tests for radix sort, heap sort, insertion sort

  • added benchmarking JMH tests

  • improved test coverage

The summary of benchmarking:

Sequential sorting (Arrays.sort)

byte: up to 50% faster
char: 4-7 times faster
short: 2-6 times faster
int: 1.2-5 times faster
long: 1.2-5 times faster
float: 1.2-5 times faster
double: 1.2-4 times faster

Parallel sorting (Arrays.parallelSort)

int: 1.2-9 times faster
long: 1.2-9 times faster
float: 1.2-4 times faster
double: 1.2-4 times faster

AVX512 support

Vamsi Parasa suggested faster sort routines by taking advantage of AVX512 instructions, see #14227, sources of sorting were modified. Therefore, I performed benchmarking of the final version (which includes optimizations by Vamsi Parasa and optimizations from my side) on a server with CPUs supported AVX512 instructions, no regression of performance was found, see detailed benchmarking results.

High-level chart showing how the actual sorting algorithm is selected
based on parallel/sequential and input size

int/long/float/double

if size < MAX_INSERTION_SORT_SIZE(=51) => [ mixed ] insertion sort
if array is almost sorted and size > MIN_MERGING_SORT_SIZE(=512) => merging sort
if recursion depth > MAX_RECURSION_DEPTH(=64) => heap sort
if random data => two pivots quicksort, else => one pivot quicksort

byte

if size < MAX_INSERTION_SORT_SIZE(=51) => insertion sort
else => counting sort

char/short

if size > MIN_COUNTING_SORT_SIZE(640) => counting sort
if size < MAX_INSERTION_SORT_SIZE(=51) => insertion sort
if recursion depth > MAX_RECURSION_DEPTH(=64) => counting sort
if random data => two pivots quicksort, else => one pivot quicksort

parallel sorting (int/long/float/double)

if size < MIN_PARALLEL_SORT_SIZE(3K) => sequential sort
invoke parallel merge sort, depth depends on parallelism level
then switch to parallel quicksort.

Progress

  • Change must be properly reviewed (1 review required, with at least 1 Reviewer)
  • Change must not contain extraneous whitespace
  • Commit message must refer to an issue

Issue

  • JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort) (Enhancement - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/27411/head:pull/27411
$ git checkout pull/27411

Update a local copy of the PR:
$ git checkout pull/27411
$ git pull https://git.openjdk.org/jdk.git pull/27411/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 27411

View PR using the GUI difftool:
$ git pr show -t 27411

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/27411.diff

Using Webrev

Link to Webrev Comment

@VladimirIaroslavski
JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort)
a040fa6 
The main achievements

- introduced Radix in parallel sorting which shows several times boost of performance and has linear complexity instead of n*ln(n)
- improved mixed insertion sort (makes whole sorting faster)
- improved merging sort for almost sorted data
- optimized parallel sorting
- improved step for pivot candidates and pivot partitioning
- suggested better buffer allocation: if no memory, it is switched to in-place sorting with no OutOfMemoryError
- minor javadoc and comment changes

- extended existing tests
- added tests for radix sort, heap sort, insertion sort
- added benchmarking JMH tests
- improved test coverage
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bridgekeeper bot commented Sep 21, 2025

👋 Welcome back VladimirIaroslavski! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

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openjdk bot commented Sep 21, 2025

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

@openjdk openjdk bot changed the title JDK-8266431: Dual-Pivot Quicksort improvements (Radix sort) 8266431: Dual-Pivot Quicksort improvements (Radix sort) Sep 21, 2025
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openjdk bot commented Sep 21, 2025 •
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@VladimirIaroslavski The following label will be automatically applied to this pull request:

  • core-libs

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@VladimirIaroslavski
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Sorting on a server with AVX512 instructions

OS name: Fedora Linux 38 (Workstation Edition)
Model name: Intel(R) Xeon(R) Gold 6338 CPU @ 2.00GHz
CPU family: 6
Model: 106
Thread(s) per core: 2
Core(s) per socket: 32
Socket(s): 2

OpenJDK version "24-beta" 2025-03-18
OpenJDK Runtime Environment Zulu24+53-CA (build 24-beta+22)
OpenJDK 64-Bit Server VM Zulu24+53-CA (build 24-beta+22, mixed mode, sharing)

Sequential sorting

Benchmark Data Type Array Size Baseline (us/op) New version (us/op) Speedup
byte RANDOM 600 1,105 1,096 1.01
byte RANDOM 3000 3,315 3,015 1.10
byte RANDOM 40000 41,283 36,735 1.12
byte RANDOM 800000 472,986 371,946 1.27
byte RANDOM 5000000 2958,884 2359,100 1.25
byte SHUFFLE 600 1,025 1,025 1.00
byte SHUFFLE 3000 3,110 2,995 1.04
byte SHUFFLE 40000 37,507 34,698 1.08
byte SHUFFLE 800000 440,601 353,063 1.25
byte SHUFFLE 5000000 2645,334 2220,906 1.19
byte STAGGER 600 0,682 0,696 0.98
byte STAGGER 3000 2,473 2,498 0.99
byte STAGGER 40000 16,892 17,167 0.98
byte STAGGER 800000 340,018 334,596 1.02
byte STAGGER 5000000 2171,872 2180,550 1.00
byte REPEATED 600 0,824 0,840 0.98
byte REPEATED 3000 2,435 2,448 0.99
byte REPEATED 40000 29,167 29,168 1.00
byte REPEATED 800000 592,413 592,667 1.00
byte REPEATED 5000000 3792,008 3791,389 1.00
--- --- --- --- --- ---
char RANDOM 600 8,076 5,811 1.39
char RANDOM 3000 127,738 18,471 6.92
char RANDOM 40000 466,992 464,783 1.00
char RANDOM 800000 1962,639 2007,212 0.98
char RANDOM 5000000 6608,751 6730,025 0.98
char SHUFFLE 600 4,713 3,574 1.32
char SHUFFLE 3000 86,595 10,962 7.90
char SHUFFLE 40000 116,087 103,458 1.12
char SHUFFLE 800000 802,059 747,908 1.07
char SHUFFLE 5000000 3527,583 3273,802 1.08
char STAGGER 600 9,146 5,651 1.62
char STAGGER 3000 88,480 9,888 8.95
char STAGGER 40000 140,569 129,855 1.08
char STAGGER 800000 694,116 701,170 0.99
char STAGGER 5000000 3685,380 3667,346 1.00
char REPEATED 600 1,775 1,745 1.02
char REPEATED 3000 87,272 17,176 5.08
char REPEATED 40000 116,472 88,054 1.32
char REPEATED 800000 789,963 660,936 1.20
char REPEATED 5000000 4373,931 3907,108 1.12
--- --- --- --- --- ---
short RANDOM 600 8,433 5,455 1.55
short RANDOM 3000 95,889 9,871 9.71
short RANDOM 40000 526,723 457,268 1.15
short RANDOM 800000 1991,657 2011,202 0.99
short RANDOM 5000000 6592,367 6745,836 0.98
short SHUFFLE 600 4,706 3,597 1.31
short SHUFFLE 3000 44,413 11,895 3.73
short SHUFFLE 40000 137,088 139,490 0.98
short SHUFFLE 800000 851,142 813,856 1.05
short SHUFFLE 5000000 3605,340 3642,393 0.99
short STAGGER 600 8,932 5,088 1.76
short STAGGER 3000 54,740 11,432 4.79
short STAGGER 40000 141,403 104,327 1.36
short STAGGER 800000 739,105 755,126 0.98
short STAGGER 5000000 3613,685 3649,485 0.99
short REPEATED 600 1,787 1,646 1.09
short REPEATED 3000 41,117 17,711 2.32
short REPEATED 40000 67,597 62,072 1.09
short REPEATED 800000 725,665 635,773 1.14
short REPEATED 5000000 3961,620 3910,409 1.01
--- --- --- --- --- ---
int RANDOM 600 10,062 6,263 1.61
int RANDOM 3000 106,288 81,867 1.30
int RANDOM 40000 2706,821 2409,536 1.12
int RANDOM 800000 70786,294 63018,686 1.12
int RANDOM 5000000 513654,721 448534,136 1.15
int SHUFFLE 600 5,554 3,832 1.45
int SHUFFLE 3000 34,681 23,799 1.46
int SHUFFLE 40000 810,646 675,154 1.20
int SHUFFLE 800000 17786,842 13394,929 1.33
int SHUFFLE 5000000 103972,483 89292,885 1.16
int STAGGER 600 10,912 1,919 5.69
int STAGGER 3000 16,805 8,743 1.92
int STAGGER 40000 221,680 119,119 1.86
int STAGGER 800000 4439,270 2646,225 1.68
int STAGGER 5000000 28206,856 18989,937 1.49
int REPEATED 600 1,600 1,401 1.14
int REPEATED 3000 8,333 8,166 1.02
int REPEATED 40000 366,056 338,253 1.08
int REPEATED 800000 8381,340 7163,611 1.17
int REPEATED 5000000 57009,039 49579,605 1.15
--- --- --- --- --- ---
long RANDOM 600 9,526 5,500 1.73
long RANDOM 3000 106,262 81,212 1.31
long RANDOM 40000 2642,178 2380,290 1.11
long RANDOM 800000 71082,533 60574,668 1.17
long RANDOM 5000000 497591,181 441894,477 1.13
long SHUFFLE 600 5,003 3,666 1.36
long SHUFFLE 3000 39,157 24,116 1.62
long SHUFFLE 40000 731,785 653,146 1.12
long SHUFFLE 800000 18055,584 14313,625 1.26
long SHUFFLE 5000000 122763,113 85477,515 1.44
long STAGGER 600 8,668 2,020 4.29
long STAGGER 3000 59,460 9,874 6.02
long STAGGER 40000 888,697 142,874 6.22
long STAGGER 800000 19205,162 3480,767 5.52
long STAGGER 5000000 123337,211 26088,945 4.73
long REPEATED 600 1,764 1,618 1.09
long REPEATED 3000 9,284 8,147 1.14
long REPEATED 40000 370,378 320,390 1.16
long REPEATED 800000 8546,204 7641,426 1.12
long REPEATED 5000000 57714,600 50890,207 1.13
--- --- --- --- --- ---
float RANDOM 600 9,229 6,824 1.35
float RANDOM 3000 98,336 94,386 1.04
float RANDOM 40000 2737,466 2626,643 1.04
float RANDOM 800000 71064,995 67788,935 1.05
float RANDOM 5000000 511617,741 483790,193 1.06
float SHUFFLE 600 5,356 4,482 1.20
float SHUFFLE 3000 32,069 27,485 1.17
float SHUFFLE 40000 803,721 786,535 1.02
float SHUFFLE 800000 17475,458 15571,843 1.12
float SHUFFLE 5000000 104055,032 103707,582 1.00
float STAGGER 600 9,823 2,259 4.35
float STAGGER 3000 21,148 10,721 1.97
float STAGGER 40000 280,128 145,725 1.92
float STAGGER 800000 5625,923 3227,219 1.74
float STAGGER 5000000 35646,533 22611,370 1.58
float REPEATED 600 2,489 2,273 1.10
float REPEATED 3000 14,390 11,444 1.26
float REPEATED 40000 537,690 456,280 1.18
float REPEATED 800000 11733,707 10678,972 1.10
float REPEATED 5000000 78247,675 58791,233 1.33
--- --- --- --- --- ---
double RANDOM 600 9,209 6,879 1.34
double RANDOM 3000 100,158 89,748 1.12
double RANDOM 40000 2744,205 2589,135 1.06
double RANDOM 800000 71450,447 67051,035 1.07
double RANDOM 5000000 518599,968 482903,685 1.07
double SHUFFLE 600 5,424 4,574 1.19
double SHUFFLE 3000 31,738 27,942 1.14
double SHUFFLE 40000 787,763 776,840 1.01
double SHUFFLE 800000 17492,549 16081,350 1.09
double SHUFFLE 5000000 107874,866 107086,811 1.01
double STAGGER 600 9,883 2,206 4.48
double STAGGER 3000 19,615 10,908 1.80
double STAGGER 40000 270,368 151,057 1.79
double STAGGER 800000 5504,383 3658,210 1.50
double STAGGER 5000000 37996,995 29044,386 1.31
double REPEATED 600 2,548 2,260 1.13
double REPEATED 3000 14,333 12,515 1.15
double REPEATED 40000 544,588 459,425 1.19
double REPEATED 800000 11791,047 10734,706 1.10
double REPEATED 5000000 79668,645 62098,296 1.28

Parallel sorting

Benchmark Data Type Array Size Baseline (us/op) New version (us/op) Speedup
int RANDOM 600 9,724 6,154 1.58
int RANDOM 3000 96,070 85,794 1.12
int RANDOM 40000 414,904 282,580 1.47
int RANDOM 800000 4743,790 1429,808 3.32
int RANDOM 5000000 23981,879 13549,869 1.77
int SHUFFLE 600 6,029 3,632 1.66
int SHUFFLE 3000 37,097 22,772 1.63
int SHUFFLE 40000 193,044 97,703 1.98
int SHUFFLE 800000 1769,768 900,230 1.97
int SHUFFLE 5000000 11040,155 7635,319 1.45
int STAGGER 600 10,948 2,366 4.63
int STAGGER 3000 15,728 11,559 1.36
int STAGGER 40000 76,648 65,278 1.17
int STAGGER 800000 912,780 532,419 1.71
int STAGGER 5000000 5528,946 2886,539 1.92
int REPEATED 600 2,000 1,588 1.26
int REPEATED 3000 10,518 8,022 1.31
int REPEATED 40000 153,249 101,689 1.51
int REPEATED 800000 2564,321 1102,722 2.33
int REPEATED 5000000 16141,658 6440,913 2.51
--- --- --- --- --- ---
long RANDOM 600 9,392 5,974 1.57
long RANDOM 3000 119,022 72,486 1.64
long RANDOM 40000 446,894 327,094 1.37
long RANDOM 800000 4618,046 2157,313 2.14
long RANDOM 5000000 26806,347 17064,431 1.57
long SHUFFLE 600 5,037 3,991 1.26
long SHUFFLE 3000 39,226 28,969 1.35
long SHUFFLE 40000 188,613 117,552 1.60
long SHUFFLE 800000 2203,806 1436,670 1.53
long SHUFFLE 5000000 15363,291 10869,309 1.41
long STAGGER 600 10,616 2,506 4.24
long STAGGER 3000 15,545 13,073 1.19
long STAGGER 40000 94,714 71,397 1.33
long STAGGER 800000 1263,737 933,039 1.35
long STAGGER 5000000 8534,961 5804,477 1.47
long REPEATED 600 1,726 1,640 1.05
long REPEATED 3000 10,035 7,876 1.27
long REPEATED 40000 168,700 110,725 1.52
long REPEATED 800000 2845,738 1504,553 1.89
long REPEATED 5000000 18759,763 9377,812 2.00
--- --- --- --- --- ---
float RANDOM 600 9,931 6,936 1.43
float RANDOM 3000 119,779 99,573 1.20
float RANDOM 40000 476,756 392,104 1.22
float RANDOM 800000 4930,482 2919,610 1.69
float RANDOM 5000000 29463,322 17644,605 1.67
float SHUFFLE 600 5,459 4,543 1.20
float SHUFFLE 3000 32,297 27,887 1.16
float SHUFFLE 40000 235,827 181,163 1.30
float SHUFFLE 800000 2428,839 1791,028 1.36
float SHUFFLE 5000000 15353,423 10433,192 1.47
float STAGGER 600 9,779 2,415 4.05
float STAGGER 3000 18,693 11,581 1.61
float STAGGER 40000 117,526 79,751 1.47
float STAGGER 800000 1744,397 1160,997 1.50
float STAGGER 5000000 10651,683 7002,571 1.52
float REPEATED 600 2,651 2,262 1.17
float REPEATED 3000 15,812 11,984 1.32
float REPEATED 40000 270,629 155,697 1.74
float REPEATED 800000 5450,441 1741,966 3.13
float REPEATED 5000000 34499,266 10705,402 3.22
--- --- --- --- --- ---
double RANDOM 600 9,183 6,965 1.32
double RANDOM 3000 97,578 94,393 1.03
double RANDOM 40000 468,966 410,451 1.14
double RANDOM 800000 5202,712 3569,054 1.46
double RANDOM 5000000 32081,048 22927,051 1.40
double SHUFFLE 600 5,462 4,438 1.23
double SHUFFLE 3000 31,924 27,371 1.17
double SHUFFLE 40000 263,423 199,992 1.32
double SHUFFLE 800000 2826,594 2387,148 1.18
double SHUFFLE 5000000 19212,580 16573,293 1.16
double STAGGER 600 9,803 2,558 3.83
double STAGGER 3000 19,258 13,093 1.47
double STAGGER 40000 133,250 107,261 1.24
double STAGGER 800000 2027,997 1561,934 1.30
double STAGGER 5000000 14387,512 10943,813 1.31
double REPEATED 600 2,553 2,266 1.13
double REPEATED 3000 14,479 11,995 1.21
double REPEATED 40000 274,235 167,220 1.64
double REPEATED 800000 5378,801 2182,560 2.46
double REPEATED 5000000 35181,974 14323,815 2.46

@VladimirIaroslavski
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Sorting on a computer without AVX512 support

OS name: Edition Windows 10 Pro
Processor: Intel(R) Core(TM) i7-10850H CPU @ 2.70GHz
System type: 64-bit operating system, x64-based processor
Version: 22H2

OpenJDK 26-ea 2026-03-17
OpenJDK Runtime Environment (build 26-ea+13-1333)
OpenJDK 64-Bit Server VM (build 26-ea+13-1333, mixed mode, sharing)

Sequential sorting

Benchmark Data Type Array Size Baseline (us/op) New version (us/op) Speedup
byte RANDOM 600 1,336 1,341 1.00
byte RANDOM 3000 3,775 3,813 0.99
byte RANDOM 40000 30,852 31,590 0.98
byte RANDOM 800000 526,780 526,931 1.00
byte RANDOM 5000000 3427,225 3466,470 0.99
byte SHUFFLE 600 1,253 1,260 0.99
byte SHUFFLE 3000 3,456 3,526 0.98
byte SHUFFLE 40000 30,739 31,153 0.99
byte SHUFFLE 800000 506,622 507,776 1.00
byte SHUFFLE 5000000 3358,144 3340,962 1.01
byte STAGGER 600 0,926 0,903 1.03
byte STAGGER 3000 2,463 2,489 0.99
byte STAGGER 40000 26,155 25,906 1.01
byte STAGGER 800000 501,954 504,353 1.00
byte STAGGER 5000000 3264,418 3268,509 1.00
byte REPEATED 600 0,978 0,634 1.54
byte REPEATED 3000 2,870 2,532 1.13
byte REPEATED 40000 30,026 28,714 1.05
byte REPEATED 800000 571,674 571,686 1.00
byte REPEATED 5000000 3740,136 3744,403 1.00
--- --- --- --- --- ---
char RANDOM 600 11,029 6,696 1.65
char RANDOM 3000 106,682 11,737 9.09
char RANDOM 40000 518,084 509,866 1.02
char RANDOM 800000 2251,095 2296,499 0.98
char RANDOM 5000000 8126,281 8208,779 0.99
char SHUFFLE 600 6,646 4,382 1.52
char SHUFFLE 3000 91,039 12,664 7.19
char SHUFFLE 40000 163,862 162,688 1.01
char SHUFFLE 800000 991,965 981,299 1.01
char SHUFFLE 5000000 4388,959 4477,596 0.98
char STAGGER 600 11,344 6,691 1.70
char STAGGER 3000 74,156 12,469 5.95
char STAGGER 40000 138,021 138,125 1.00
char STAGGER 800000 905,072 869,419 1.04
char STAGGER 5000000 5075,574 5076,498 1.00
char REPEATED 600 1,796 1,675 1.07
char REPEATED 3000 72,315 17,109 4.23
char REPEATED 40000 100,150 99,830 1.00
char REPEATED 800000 788,861 728,818 1.08
char REPEATED 5000000 4534,875 4417,603 1.03
--- --- --- --- --- ---
short RANDOM 600 11,147 6,657 1.67
short RANDOM 3000 97,153 14,013 6.93
short RANDOM 40000 536,996 533,115 1.01
short RANDOM 800000 2214,721 2236,256 0.99
short RANDOM 5000000 8129,979 8305,536 0.98
short SHUFFLE 600 6,466 4,328 1.49
short SHUFFLE 3000 37,262 14,628 2.55
short SHUFFLE 40000 151,558 151,465 1.00
short SHUFFLE 800000 952,759 961,413 0.99
short SHUFFLE 5000000 4392,945 4481,849 0.98
short STAGGER 600 11,456 6,737 1.70
short STAGGER 3000 42,934 14,630 2.93
short STAGGER 40000 122,307 120,126 1.02
short STAGGER 800000 837,886 858,188 0.98
short STAGGER 5000000 5099,399 5063,530 1.01
short REPEATED 600 1,797 1,673 1.07
short REPEATED 3000 36,409 18,124 2.01
short REPEATED 40000 68,712 64,305 1.07
short REPEATED 800000 748,089 676,263 1.11
short REPEATED 5000000 4509,726 4354,061 1.04
--- --- --- --- --- ---
int RANDOM 600 12,799 8,529 1.50
int RANDOM 3000 168,717 151,504 1.11
int RANDOM 40000 3053,482 2663,760 1.15
int RANDOM 800000 77058,078 68039,633 1.13
int RANDOM 5000000 553486,331 483191,027 1.15
int SHUFFLE 600 7,091 5,090 1.39
int SHUFFLE 3000 57,823 37,976 1.52
int SHUFFLE 40000 982,797 804,192 1.22
int SHUFFLE 800000 20170,567 15124,860 1.33
int SHUFFLE 5000000 119944,448 101314,175 1.18
int STAGGER 600 12,372 2,332 5.31
int STAGGER 3000 18,185 11,073 1.64
int STAGGER 40000 263,148 149,947 1.75
int STAGGER 800000 5206,958 3003,595 1.73
int STAGGER 5000000 33070,195 20196,353 1.64
int REPEATED 600 1,850 1,689 1.10
int REPEATED 3000 19,935 16,725 1.19
int REPEATED 40000 427,379 426,491 1.00
int REPEATED 800000 8780,449 8693,568 1.01
int REPEATED 5000000 59041,332 53085,389 1.11
--- --- --- --- --- ---
long RANDOM 600 12,759 8,332 1.53
long RANDOM 3000 170,641 153,686 1.11
long RANDOM 40000 3102,722 2702,462 1.15
long RANDOM 800000 76062,436 68565,859 1.11
long RANDOM 5000000 550540,619 488863,464 1.13
long SHUFFLE 600 7,482 5,153 1.45
long SHUFFLE 3000 53,436 39,168 1.36
long SHUFFLE 40000 980,789 803,654 1.22
long SHUFFLE 800000 20833,103 15763,843 1.32
long SHUFFLE 5000000 122366,475 104073,072 1.18
long STAGGER 600 12,709 2,299 5.53
long STAGGER 3000 19,001 11,054 1.72
long STAGGER 40000 275,147 165,269 1.66
long STAGGER 800000 5466,681 3912,351 1.40
long STAGGER 5000000 37297,708 29582,068 1.26
long REPEATED 600 2,107 1,681 1.25
long REPEATED 3000 16,612 9,562 1.74
long REPEATED 40000 426,694 421,148 1.01
long REPEATED 800000 8904,279 8561,931 1.04
long REPEATED 5000000 60695,788 54597,570 1.11
--- --- --- --- --- ---
float RANDOM 600 12,991 9,693 1.34
float RANDOM 3000 175,275 167,552 1.05
float RANDOM 40000 3138,437 2962,572 1.06
float RANDOM 800000 79635,198 75467,573 1.06
float RANDOM 5000000 572424,359 536613,819 1.07
float SHUFFLE 600 7,568 6,270 1.21
float SHUFFLE 3000 54,735 43,874 1.25
float SHUFFLE 40000 992,473 912,560 1.09
float SHUFFLE 800000 20273,495 17291,888 1.17
float SHUFFLE 5000000 120219,159 113983,042 1.05
float STAGGER 600 13,936 2,911 4.79
float STAGGER 3000 23,105 13,149 1.76
float STAGGER 40000 307,735 179,749 1.71
float STAGGER 800000 22328,783 3838,253 5.82
float STAGGER 5000000 143354,475 27434,381 5.23
float REPEATED 600 2,952 2,551 1.16
float REPEATED 3000 41,605 16,208 2.57
float REPEATED 40000 650,424 530,244 1.23
float REPEATED 800000 13124,335 11077,583 1.18
float REPEATED 5000000 85949,114 64994,047 1.32
--- --- --- --- --- ---
double RANDOM 600 13,226 9,674 1.37
double RANDOM 3000 174,235 168,003 1.04
double RANDOM 40000 3143,176 2969,988 1.06
double RANDOM 800000 80122,032 75624,728 1.06
double RANDOM 5000000 574170,519 541634,681 1.06
double SHUFFLE 600 7,350 6,258 1.17
double SHUFFLE 3000 54,996 47,801 1.15
double SHUFFLE 40000 997,654 910,188 1.10
double SHUFFLE 800000 20885,588 17842,091 1.17
double SHUFFLE 5000000 124954,149 117951,053 1.06
double STAGGER 600 13,905 3,104 4.48
double STAGGER 3000 24,836 14,530 1.71
double STAGGER 40000 315,874 208,873 1.51
double STAGGER 800000 7174,689 4755,320 1.51
double STAGGER 5000000 48635,918 34536,380 1.41
double REPEATED 600 2,963 2,577 1.15
double REPEATED 3000 29,148 16,343 1.78
double REPEATED 40000 634,175 525,211 1.21
double REPEATED 800000 13132,082 11342,063 1.16
double REPEATED 5000000 88391,737 67412,676 1.31

Parallel sorting

Benchmark Data Type Array Size Baseline (us/op) New version (us/op) Speedup
int RANDOM 600 12,794 8,505 1.50
int RANDOM 3000 168,675 151,334 1.11
int RANDOM 40000 987,834 425,065 2.32
int RANDOM 800000 19055,172 6019,487 3.17
int RANDOM 5000000 138748,345 37177,898 3.73
int SHUFFLE 600 7,072 5,122 1.38
int SHUFFLE 3000 55,693 39,086 1.42
int SHUFFLE 40000 448,901 210,483 2.13
int SHUFFLE 800000 7086,518 1789,933 3.96
int SHUFFLE 5000000 33432,965 17881,627 1.87
int STAGGER 600 12,467 2,348 5.31
int STAGGER 3000 18,100 11,108 1.63
int STAGGER 40000 185,856 91,566 2.03
int STAGGER 800000 4237,095 1092,863 3.88
int STAGGER 5000000 91703,510 9672,080 9.48
int REPEATED 600 2,039 1,693 1.20
int REPEATED 3000 19,928 16,955 1.18
int REPEATED 40000 435,095 179,503 2.42
int REPEATED 800000 8667,204 2280,028 3.80
int REPEATED 5000000 46503,601 16295,285 2.85
--- --- --- --- --- ---
long RANDOM 600 12,683 8,324 1.52
long RANDOM 3000 170,779 151,285 1.13
long RANDOM 40000 1049,755 517,177 2.03
long RANDOM 800000 19114,558 8186,756 2.33
long RANDOM 5000000 136592,625 50122,188 2.73
long SHUFFLE 600 7,507 5,317 1.41
long SHUFFLE 3000 53,452 38,660 1.38
long SHUFFLE 40000 456,876 235,079 1.94
long SHUFFLE 800000 7104,711 3026,515 2.35
long SHUFFLE 5000000 36215,812 31943,545 1.13
long STAGGER 600 12,726 2,314 5.50
long STAGGER 3000 19,204 11,076 1.73
long STAGGER 40000 188,118 117,579 1.60
long STAGGER 800000 15883,497 1604,405 9.90
long STAGGER 5000000 30772,348 19823,240 1.55
long REPEATED 600 1,958 1,681 1.16
long REPEATED 3000 19,457 9,782 1.99
long REPEATED 40000 447,956 201,816 2.22
long REPEATED 800000 8709,853 2817,039 3.09
long REPEATED 5000000 47701,874 27042,182 1.76
--- --- --- --- --- ---
float RANDOM 600 12,957 9,760 1.33
float RANDOM 3000 174,859 168,011 1.04
float RANDOM 40000 1088,187 593,148 1.83
float RANDOM 800000 19946,194 8786,492 2.27
float RANDOM 5000000 143259,840 52053,455 2.75
float SHUFFLE 600 7,524 6,261 1.20
float SHUFFLE 3000 55,272 49,120 1.13
float SHUFFLE 40000 475,746 263,484 1.81
float SHUFFLE 800000 7241,135 2634,484 2.75
float SHUFFLE 5000000 35411,419 21196,612 1.67
float STAGGER 600 13,950 2,942 4.74
float STAGGER 3000 23,098 13,183 1.75
float STAGGER 40000 237,012 128,761 1.84
float STAGGER 800000 4591,090 1751,410 2.62
float STAGGER 5000000 32436,076 14446,905 2.25
float REPEATED 600 2,885 2,549 1.13
float REPEATED 3000 40,168 16,392 2.45
float REPEATED 40000 660,494 237,183 2.78
float REPEATED 800000 12950,842 3223,258 4.02
float REPEATED 5000000 72413,630 22049,544 3.28
--- --- --- --- --- ---
double RANDOM 600 13,141 9,722 1.35
double RANDOM 3000 173,583 167,573 1.04
double RANDOM 40000 1094,277 693,851 1.58
double RANDOM 800000 20258,598 11422,502 1.77
double RANDOM 5000000 149441,199 66982,876 2.23
double SHUFFLE 600 7,350 6,198 1.19
double SHUFFLE 3000 54,795 48,204 1.14
double SHUFFLE 40000 486,034 292,594 1.66
double SHUFFLE 800000 7493,063 3994,888 1.88
double SHUFFLE 5000000 38662,773 38459,203 1.01
double STAGGER 600 14,004 3,095 4.52
double STAGGER 3000 24,786 14,442 1.72
double STAGGER 40000 265,910 166,051 1.60
double STAGGER 800000 5161,371 2329,184 2.22
double STAGGER 5000000 37595,716 25195,029 1.49
double REPEATED 600 2,958 2,575 1.15
double REPEATED 3000 24,794 16,353 1.52
double REPEATED 40000 645,872 257,590 2.51
double REPEATED 800000 13011,569 3817,908 3.41
double REPEATED 5000000 73640,263 33488,503 2.20

@VladimirIaroslavski VladimirIaroslavski mentioned this pull request Sep 21, 2025
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@bourgesl
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Nice work, Vladimir!

Congratulations for all the hard work, needed to upgrade DPQS once again!

I will look at this new PR.

@bourgesl
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Please check your file encoding (windows vs jnix) see jcheck report!

@openjdk openjdk bot added the rfr Pull request is ready for review label Sep 21, 2025
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mlbridge bot commented Sep 21, 2025 •
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Webrevs

amaembo
amaembo reviewed Sep 22, 2025
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src/java.base/share/classes/java/util/DualPivotQuicksort.java Outdated
*/
private static final int MAX_RECURSION_DEPTH = 64 * DELTA;
private static final int MAX_BUFFER_SIZE =
(int) Math.min(Runtime.getRuntime().maxMemory() >>> 4, Integer.MAX_VALUE);
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@amaembo amaembo Sep 22, 2025 •
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A small suggestion: since Java 21, you may utilize Math.clamp to avoid explicit (int) cast:

private static final int MAX_BUFFER_SIZE =
        Math.clamp(Runtime.getRuntime().maxMemory() >>> 4, 0, Integer.MAX_VALUE);

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Good point, will apply Math.clamp().

amaembo
amaembo reviewed Sep 22, 2025
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src/java.base/share/classes/java/util/DualPivotQuicksort.java Outdated
* data, taking into account parallel context.
*/
boolean isLargeRandom =
// size > MIN_RADIX_SORT_SIZE && (sorter == null || bits > 0) &&
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Do we need an outcommented line of code?

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            boolean isLargeRandom =
//              size > MIN_RADIX_SORT_SIZE && (sorter == null || bits > 0) &&
                size > MIN_RADIX_SORT_SIZE && (sorter != null && bits > 0) &&
                (a[e1] > a[e2] || a[e2] > a[e3] || a[e3] > a[e4] || a[e4] > a[e5]);

This code runs Radix sort during parallel sort only.
If you want to use Radix sort during sequential or parallel sort also,
you need to switch to the first line.

Agree, both lines should contain explanations.

If we agree to move Radix sort out from this PR, these lines go away from here.

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Have you considered a private static final boolean USE_RADIX_SORT_WITH_PARALLEL = false;? Then we don't need to comment the code, and one could flip the behavior by altering the flag

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@VladimirIaroslavski VladimirIaroslavski Sep 26, 2025 •
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Nice suggestion, will try to apply

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AlanBateman commented Sep 22, 2025 •
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Do you have any sense on if parallelSort is widely used? There is a lot of code and complexity in this proposal and I think important to understand if it is worth it.

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amaembo commented Sep 22, 2025

It would be nice to have a high-level chart showing how the actual sorting algorithm is selected based on parallel/sequential, input size and whatever else. For an outsider, it's hard to grasp the whole picture. Is radix sort used for parallel sorting only? Sorry if such a chart already exists and I missed it.

If improvements of parallel sorting and sequential sorting are at least partially independent, I think it may make sense to deliver them in separate PRs. This would really simplify the review process.

@VladimirIaroslavski
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Alan, Tagir,

Thank you for your comments!

New version of sources contains optimizations of sequential and parallel sorts, such as, improvements of insertion sort, better partitioning, better pivot selection, merging sort and counting sort (for byte/char/short).
At the same time Radix sort is introduced. And of course, these parts are independent.

I think also it makes sense to separate this PR into two pull requests.

Do you agree, if I move Radix sort out from this PR and re-run benchmarking?
And later, after integration of these optimizations, we will return to discussion of Radix sort,
what do you think?

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AlanBateman commented Sep 23, 2025 •
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Do you agree, if I move Radix sort out from this PR and re-run benchmarking? And later, after integration of these optimizations, we will return to discussion of Radix sort, what do you think?

Yes, splitting this into two would be good as it allow both proposals to be discussed/reviewed on their own merit.

@VladimirIaroslavski
JDK-8266431: Dual-Pivot Quicksort improvements
a6cc6a0 
* Moved Radix sort out from sorting
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VladimirIaroslavski commented Sep 26, 2025 •
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It would be nice to have a high-level chart showing how the actual sorting algorithm is selected based on parallel/sequential, input size and whatever else. For an outsider, it's hard to grasp the whole picture. Is radix sort used for parallel sorting only? Sorry if such a chart already exists and I missed it.

If improvements of parallel sorting and sequential sorting are at least partially independent, I think it may make sense to deliver them in separate PRs. This would really simplify the review process.

I added the chart to the first post, thank you for advice!

@VladimirIaroslavski
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I moved Radix sort out from sources and re-run benchmarking of parallel sorting.
We can see that new parallel sorting is still faster than existing version in JDK,
no degradation.

Parallel sorting (without Radix sort)

Benchmark Data Type Array Size Baseline (us/op) New version (us/op) Speedup
int RANDOM 600 12,852 8,507 1.51
int RANDOM 3000 168,764 152,866 1.10
int RANDOM 40000 987,272 647,195 1.53
int RANDOM 800000 19120,539 13251,660 1.44
int RANDOM 5000000 133598,983 90992,272 1.47
int SHUFFLE 600 7,165 5,136 1.40
int SHUFFLE 3000 56,363 39,100 1.44
int SHUFFLE 40000 454,965 233,097 1.95
int SHUFFLE 800000 7087,698 3153,941 2.25
int SHUFFLE 5000000 32361,302 22618,240 1.43
int STAGGER 600 12,499 2,351 5.32
int STAGGER 3000 18,045 11,093 1.63
int STAGGER 40000 177,705 91,101 1.95
int STAGGER 800000 3735,779 1078,546 3.46
int STAGGER 5000000 25432,573 9705,696 2.62
int REPEATED 600 1,835 1,696 1.08
int REPEATED 3000 19,594 16,612 1.18
int REPEATED 40000 433,101 181,605 2.38
int REPEATED 800000 8680,406 2206,406 3.93
int REPEATED 5000000 46452,021 16940,200 2.74
-- -- -- -- -- --
long RANDOM 600 12,967 8,352 1.55
long RANDOM 3000 170,926 150,999 1.13
long RANDOM 40000 1048,627 666,233 1.57
long RANDOM 800000 19057,260 13713,901 1.39
long RANDOM 5000000 140089,309 93820,320 1.49
long SHUFFLE 600 7,284 5,401 1.35
long SHUFFLE 3000 54,013 39,516 1.37
long SHUFFLE 40000 454,804 255,803 1.78
long SHUFFLE 800000 7222,403 3670,639 1.97
long SHUFFLE 5000000 33815,535 31767,738 1.06
long STAGGER 600 12,821 2,311 5.55
long STAGGER 3000 19,027 11,073 1.72
long STAGGER 40000 188,118 111,978 1.68
long STAGGER 800000 4763,922 1630,149 2.92
long STAGGER 5000000 32556,841 19882,107 1.64
long REPEATED 600 1,961 1,770 1.11
long REPEATED 3000 19,678 9,766 2.01
long REPEATED 40000 439,893 201,826 2.18
long REPEATED 800000 8725,427 2817,883 3.10
long REPEATED 5000000 47688,415 26917,131 1.77
-- -- -- -- -- --
float RANDOM 600 13,048 10,256 1.27
float RANDOM 3000 175,047 167,967 1.04
float RANDOM 40000 1089,859 740,659 1.47
float RANDOM 800000 19919,657 15086,025 1.32
float RANDOM 5000000 143704,590 105425,171 1.36
float SHUFFLE 600 7,526 6,214 1.21
float SHUFFLE 3000 54,785 49,150 1.11
float SHUFFLE 40000 475,588 289,907 1.64
float SHUFFLE 800000 7221,754 4124,313 1.75
float SHUFFLE 5000000 35369,094 28281,396 1.25
float STAGGER 600 13,956 2,936 4.75
float STAGGER 3000 23,035 13,192 1.75
float STAGGER 40000 230,380 133,386 1.73
float STAGGER 800000 4614,573 1736,213 2.66
float STAGGER 5000000 34053,504 14692,088 2.32
float REPEATED 600 2,910 2,554 1.14
float REPEATED 3000 40,965 16,641 2.46
float REPEATED 40000 654,329 237,761 2.75
float REPEATED 800000 13094,558 3234,352 4.05
float REPEATED 5000000 71522,839 23208,431 3.08
-- -- -- -- -- --
double RANDOM 600 13,103 9,628 1.36
double RANDOM 3000 174,936 168,750 1.04
double RANDOM 40000 1094,699 780,827 1.40
double RANDOM 800000 20205,605 15304,877 1.32
double RANDOM 5000000 147620,455 107560,209 1.37
double SHUFFLE 600 7,359 6,191 1.19
double SHUFFLE 3000 55,208 48,141 1.15
double SHUFFLE 40000 485,528 311,081 1.56
double SHUFFLE 800000 7525,265 4723,622 1.59
double SHUFFLE 5000000 38030,224 38159,739 1.00
double STAGGER 600 14,019 3,120 4.49
double STAGGER 3000 24,778 14,510 1.71
double STAGGER 40000 241,340 151,728 1.59
double STAGGER 800000 5367,318 2353,046 2.28
double STAGGER 5000000 38446,590 25241,014 1.52
double REPEATED 600 2,986 2,586 1.15
double REPEATED 3000 32,133 16,018 2.01
double REPEATED 40000 659,864 256,873 2.57
double REPEATED 800000 13045,124 3823,682 3.41
double REPEATED 5000000 75177,194 33156,316 2.27

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