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https://issues.apache.org/jira/browse/SOLR-3109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13204737#comment-13204737
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Martijn van Groningen commented on SOLR-3109:
---------------------------------------------
No worries :-) I didn't want to move this work to anyone. Just wanted to say
that the test needs to be updated.
I put that comment b/c in the following three lines group.ngroups and
group.truncate features are tested. These features *only* work properly if
documents belonging to a group reside in the same shard. If documents belonging
to a group do occur in more than one shard then the results are very likely
incorrect.
Tomorrow I will update the test case and get this patch committed. If you want
to update the test case and have time for that that would be great!
> 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
> Attachments: 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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