The new optimized version of Dual-Pivot Quicksort

Laurent Bourgès bourges.laurent at
Fri Nov 9 09:08:45 UTC 2018

Hi Vladimir,

Thank you for your attention, you are the Sort Master.

Le ven. 9 nov. 2018 à 09:02, Vladimir Yaroslavskiy < at> a
écrit :

> Hi Laurent,
> The new version is still under review, there were a lot of suggestions and
> ideas from Doug Lea.
> I needed time to apply and check them. I'm going to send final version in
> few days.

Excellent news, so it will ship in jdk12...

> As to new method sort(a[], low, high, indices): do you mean this method in
> Arrays class?
> Are you going to extend Arrays API?

I benchmarked my MergeSort and adding extra array implies many more moves:
thresholds should be adjusted and my sort is sometimes better as it makes
half moves (a <-> buffer swaps), so this complementary sort should have its
own tuned implementation (tests & benchmarks).

I coded my sort as such need did not match any Arrays.sort() methods.
Having it publicly in jdk.base would be great for any other data handling
algorithm (science, AI ?)

If you agree it is useful, I could try proposing an Arrays/Collection API
extension like :
sort(<primitive or Value>[], low, high, int[]indices)

> About new parameters workbase[]: method sort(...) in DualPivotQuicksort
> class (version is under review)
> has extra parameter - parallel context (Sorter sorter) which has required
> workbase[].
> If we run sorting sequentially, sorter parameter is null (no any objects)
> and temporary buffer
> will be created inside in tryMerge method if we go ahead with merging.

I will have a look. For Marlin, parallel sort is not possible as rendering
shapes can be parallelized in the application (geoserver map rendering).

> I will send new sources in few days and add you in cc, so you can look at
> it
> and find if new methods are acceptable for you. Then we can discuss
> required changes (if any).

Perfect, I started adapting your code and will share soon the link to my
github repo.

> Thank you,
> Vladimir

Thank you very much for your first thoughts,

> Пятница, 9 ноября 2018, 10:44 +03:00 от Laurent Bourgès <
> bourges.laurent at>:
> Hi,
> I am currently testing many sort algorithms to improve the Marlin renderer
> (AA 2D shape rasterizer), I integrated since OpenJDK9 and am still
> improving for OpenJDK12 .
> I created my MergeSort (top down, check for sorted parts, array / buffer
> swap to minimize moves, isort on small sub arrays) that sort 2 int[]:
> crossing + edge indices.
>  It is critical as edge crossings are sorted at every scanline, data are
> almost sorted/reversed, not really random.
> 3 questions:
> - why is this patch dormant ? I checked in openjdk12 repo and your changes
> were not integrated.
> - I need a sort() method that works with 2 arrays: data + indices (pointer
> like). Such sorted indices are useful to use for lookups c[idx[k]] or to
> perform other array permutations...
> Would you agree adding such new sort(a[], low, high, indices)
> - Marlin uses a ThreadLocal context to avoid any allocation. JDK sort()
> impl do not accept parameters to give any buffer[] and avoid allocations.
> Would you agree adding such optional parameters (like workbase[]) ?
> I will experiment adapting the DualPivotQuickSort in Marlin renderer and
> perform array sort race & rendering benchmarks.
> Cheers,
> Laurent
> Le ven. 19 janv. 2018 à 14:38, Vladimir Yaroslavskiy < at
> <>> a écrit :
> Hi team,
> In Sept 2009 Josh Bloch, Jon Bentley and I introduced new sorting
> algorithm, Dual-Pivot Quicksort, for primitives in JDK 7 and later
> I suggested several improvements of Dual-Pivot Quicksort, which
> were integrated into JDK 8.
> Now I have more optimized and faster version of Dual-Pivot Quicksort.
> I have been working on it for the last 5 years. Please, find the
> summary of changes below and sources / diff at webrev [1].
> All tests and benchmarking were run on the most recent build of JDK 10,
> jdk-10-ea+39. The new version shows the better performance on different
> inputs and guarantees n*log(n) on any data.
> The new implementation of Dual-Pivot Quicksort is 'all-in-one' version:
> it contains one code for both parallel and sequential sorting algorithms.
> Suggested version is 10-20% faster on random data, 1.5-4 times faster
> on nearly structured arrays, 1.5-2 times faster on period inputs.
> Parallel Dual-Pivot Quicksort is 1.5-3 times faster than current
> algorithm based on merge sort.
> Benchmarking on the test suite, suggested by Jon Bentley, shows the
> boost of performance in 1.4 times. This test suite contains several
> types of inputs, such as random data, nearly structured arrays, data
> with period and so on. Also there are several modifications of inputs
> and parameters which are used in data building. We run sorting on all
> combinations to compare two algorithms.
> Please let me know if you have any questions / comments.
> Summary of changes:
> DualPivotQuicksort class
> ------------------------
> * Pivots are chosen with another step, the 1-st and 5-th candidates
>    are taken as pivots instead of 2-nd and 4-th.
> * Splitting into parts is related to the golden ratio
> * Pivot candidates are sorted by combination of 5-element
>    network sorting + insertion sort
> * New backwards partitioning is simpler and more efficient
> * Quicksort tuning parameters were updated
> * Merging sort is invoked on each iteration from Quicksort
> * Additional steps for float/double were fully rewritten
> * Heap sort is invoked on the leftmost part
> * Heap sort is used as a guard against quadratic time
> * Parallel sorting is based on Dual-Pivot Quicksort
>    instead of merge sort
> SortingAlgorithms class
> -----------------------
> * Merging sort and pair insertion sort were moved from
>    DualPivotQuicksort class
> * Pair insertion sort was simplified and optimized
> * New nano insertion sort was introduced for tiny arrays
> * Merging sort was fully rewritten
> * Optimized merging partitioning is used
> * Merging parameters were updated
> * Merging of runs was fully rewritten
> * Fast version of heap sort was introduced
> * Parallel merging sort was also provided
> Sorting / ParallelSorting classes
> ---------------------------------
> * New test cases were added
> * Sources of these classes were unified
> Arrays class
> ------------
> * Calls of Dual-Pivot Quicksort were updated
> * Parallel sorting of primitives was switched to parallel
>    Dual-Pivot Quicksort
> * Javadoc was modified
> ArraysParallelSortHelpers class
> -------------------------------
> * Old implementation of parallel sorting for primitives was removed
> * Javadoc was updated
> Thank you,
> Vladimir
> --------------------------------------------------------------------
> [1]
> --------------------------------------------------------------------
> --
> Vladimir Yaroslavskiy

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