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From "Dawid Weiss (Commented) (JIRA)" <>
Subject [jira] [Commented] (LUCENE-3972) Improve AllGroupsCollector implementations
Date Thu, 12 Apr 2012 13:53:18 GMT


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):
    public static int rehash(int k)
        k ^= k >>> 16;
        k *= 0x85ebca6b;
        k ^= k >>> 13;
        k *= 0xc2b2ae35;
        k ^= k >>> 16;
        return k;
> Improve AllGroupsCollector implementations
> ------------------------------------------
>                 Key: LUCENE-3972
>                 URL:
>             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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