> On 16 Aug 2016, at 20:08, Tagir F. Valeev <amae...@gmail.com> wrote:
>
> Hello, Paul!
>
> Thank you. Here's issue:
> https://bugs.openjdk.java.net/browse/JDK-8164189
> And webrev:
> http://cr.openjdk.java.net/~tvaleev/webrev/8164189/r1/
>
Thanks will push today or tomorrow,
Paul.
> With best regards,
> Tagir Valeev.
>
> PS> Hi Tagir,
>
> PS> I like it. Please open an issue and i will sponsor the fix for you.
>
> PS> Thanks,
> PS> Paul.
>
>>> On 8 Aug 2016, at 22:31, Tagir F. Valeev <amae...@gmail.com> wrote:
>>>
>>> Hello!
>>>
>>> I'd like to propose a simple performance patch for Collectors.toSet():
>>>
>>> --- a/src/java.base/share/classes/java/util/stream/Collectors.java Tue
>>> Aug 02 07:19:06 2016 +0530
>>> +++ b/src/java.base/share/classes/java/util/stream/Collectors.java Tue
>>> Aug 09 11:47:20 2016 +0700
>>> @@ -295,7 +295,12 @@
>>> public static <T>
>>> Collector<T, ?, Set<T>> toSet() {
>>> return new CollectorImpl<>((Supplier<Set<T>>) HashSet::new, Set::add,
>>> - (left, right) -> { left.addAll(right);
>>> return left; },
>>> + (left, right) -> {
>>> + if (left.size() < right.size()) {
>>> + right.addAll(left); return
>>> right;
>>> + }
>>> + left.addAll(right); return left;
>>> + },
>>> CH_UNORDERED_ID);
>>> }
>>>
>>> This will add the smaller set to the larger which may improve parallel
>>> performance when subtasks produced uneven results. In normal case the
>>> additional overhead is insignificant (additional HashSet size
>>> comparison per each combine operation which usually performed
>>> ~4*parallelism times).
>>>
>>> Here's simple JDK benchmark with results (Core-i7-4702MQ 4 HT cores,
>>> Win7, JDK 9-ea+129 64bit) which confirms the speedup:
>>> http://cr.openjdk.java.net/~tvaleev/patches/toSet/
>>>
>>> When data is unevenly distributed, it's significantly faster:
>>>
>>> Original:
>>> ToSet.toSetParallel 10000 true avgt 50 88,580 ± 0,874
>>> us/op
>>> ToSet.toSetParallel 100000 true avgt 50 676,243 ± 41,188
>>> us/op
>>> ToSet.toSetParallel 1000000 true avgt 50 9126,399 ± 83,260
>>> us/op
>>> Patched:
>>> ToSet.toSetParallel 10000 true avgt 50 62,121 ± 1,207
>>> us/op
>>> ToSet.toSetParallel 100000 true avgt 50 556,968 ± 37,404
>>> us/op
>>> ToSet.toSetParallel 1000000 true avgt 50 6572,372 ± 183,466
>>> us/op
>>>
>>> When data is evenly distributed, no statistically significant changes
>>> observed:
>>>
>>> Original:
>>> ToSet.toSetParallel 10000 false avgt 50 177,137 ± 5,941
>>> us/op
>>> ToSet.toSetParallel 100000 false avgt 50 2056,332 ± 87,433
>>> us/op
>>> ToSet.toSetParallel 1000000 false avgt 50 51864,198 ± 560,883
>>> us/op
>>> Patched:
>>> ToSet.toSetParallel 10000 false avgt 50 172,606 ± 7,321
>>> us/op
>>> ToSet.toSetParallel 100000 false avgt 50 1922,478 ± 79,593
>>> us/op
>>> ToSet.toSetParallel 1000000 false avgt 50 52648,100 ± 621,526
>>> us/op
>>>
>>> What do you think? Should I open an issue?
>>>
>>> With best regards,
>>> Tagir Valeev.
>>>
>
