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https://issues.apache.org/jira/browse/SOLR-3109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13205088#comment-13205088
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Greg Bowyer commented on SOLR-3109:
-----------------------------------
Its for the 3.5 branch, but like I said I was jumping the gun, if your patch
applies forget mine and go with that
> group=true requests result in numerous redundant shard requests
> ---------------------------------------------------------------
>
> Key: SOLR-3109
> URL: https://issues.apache.org/jira/browse/SOLR-3109
> Project: Solr
> Issue Type: Bug
> Components: search
> Affects Versions: 3.5, 4.0
> Environment: 64-bit Linux, sharded environment
> Reporter: Russell Black
> Assignee: Martijn van Groningen
> Priority: Critical
> Labels: patch, performance
> Fix For: 3.6, 4.0
>
> Attachments:
> SOLR-3109-Backport-of-grouping-performace-fix-to-3.x.patch,
> SOLR-3109-lucene_solr_3_5.patch, SOLR-3109.patch, SOLR-3109.patch,
> SOLR-3109.patch
>
>
> During the second phase of a group query, the collator sends a query to each
> of the shards. The purpose of this query is for shards to respond with the
> doc ids that match the set of group ids returned from the first phase. The
> problem is that it sends this second query to each shard multiple times.
> Specifically, in an environment with n shards, each shard will be hit with an
> identical query n times during the second phase of query processing,
> resulting in O(_n_ ^2^) performance where _n_ is the number of shards.
> I have traced this bug down to a single line in
> {{TopGroupsShardRequestFactory.java}}, and I am attaching a patch.
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