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/
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.
>>
