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https://issues.apache.org/jira/browse/LUCENE-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252427#comment-13252427
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Dawid Weiss commented on LUCENE-3972:
-------------------------------------
This is curious indeed. One thing to check would be this: SentinelIntSet uses
no key rehashing (rehash simply returns the key). This resulted in very poor
performance for certain regular integer sets (my experience from implementing
HPPC). So while rehashing may seem like an additional overhead, it actually
boosts performance.
Martijn -- could you patch the trunk's SentinelIntSet#rehash with, for example,
this (murmur hash3 tail):
{noformat}
public static int rehash(int k)
{
k ^= k >>> 16;
k *= 0x85ebca6b;
k ^= k >>> 13;
k *= 0xc2b2ae35;
k ^= k >>> 16;
return k;
}
{noformat}
> Improve AllGroupsCollector implementations
> ------------------------------------------
>
> Key: LUCENE-3972
> URL: https://issues.apache.org/jira/browse/LUCENE-3972
> Project: Lucene - Java
> Issue Type: Improvement
> Components: modules/grouping
> Reporter: Martijn van Groningen
> Attachments: LUCENE-3972.patch, LUCENE-3972.patch
>
>
> I think that the performance of TermAllGroupsCollectorm,
> DVAllGroupsCollector.BR and DVAllGroupsCollector.SortedBR can be improved by
> using BytesRefHash to store the groups instead of an ArrayList.
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