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From "Martijn van Groningen (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-3109) group=true requests result in numerous redundant shard requests
Date Mon, 13 Feb 2012 00:15:02 GMT

    [ https://issues.apache.org/jira/browse/SOLR-3109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13206571#comment-13206571
] 

Martijn van Groningen commented on SOLR-3109:
---------------------------------------------

{quote}
The current TestDistributedGrouping test case is constructed in such a way that each record
has a unique value for it's search group field (i1), so that there is never more than one
record in any given search group. This style of indexing conforms to the restriction discussed
earlier. This is likely the reason there were no test failures.
{quote}
I think this issue doesn't exist in the released versions of Solr / 4.0-dev. Due to the bug
that all shards were queried for each ShardRequest instance and all the matching top search
groups still arrived at the right shard. Only after applying the changes to TopGroupsShardRequestFactory
I could let the distributed grouping test fail.
                
> 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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