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From "Russell Black (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-3109) group=true requests result in numerous redundant shard requests
Date Thu, 09 Feb 2012 17:06:05 GMT

    [ https://issues.apache.org/jira/browse/SOLR-3109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13204653#comment-13204653
] 

Russell Black commented on SOLR-3109:
-------------------------------------

In {{TestDistributedGrouping}} you wrote the following comment:

{code}
 // In order to validate this we need to make sure that during indexing that all documents
of one group only occur on the same shard
{code}

I wanted to understand the reason for that comment before making any changes to the test case.
 (Assuming you wanted me to update the test case -- if not, I'll leave the test case in your
hands)
                
> 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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