[jira] [Commented] (LUCENE-4832) Unbounded getTopGroups for ToParentBlockJoinCollector

["Michael McCandless (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-4832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13602498#comment-13602498 ] 

Michael McCandless commented on LUCENE-4832:
--------------------------------------------

Could we just fix it so passing in Integer.MAX_VALUE for maxDocsPerGroup works?  I.e., we'd need to do the min(numDocsInGroup, maxDocsPerGroup) when we create the collector for the group.  And I think we don't need to create this separate Accumulator class...
                
> Unbounded getTopGroups for ToParentBlockJoinCollector
> -----------------------------------------------------
>
>                 Key: LUCENE-4832
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4832
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: modules/join
>            Reporter: Aleksey Aleev
>         Attachments: LUCENE-4832.patch
>
>
> _ToParentBlockJoinCollector#getTopGroups_ method takes several arguments:
> {code:java}
> public TopGroups<Integer> getTopGroups(ToParentBlockJoinQuery query, 
>                                        Sort withinGroupSort,
>                                        int offset,
>                                        int maxDocsPerGroup,
>                                        int withinGroupOffset,
>                                        boolean fillSortFields)
> {code}
> and one of them is {{maxDocsPerGroup}} which specifies upper bound of child documents number returned within each group. 
> {{ToParentBlockJoinCollector}} collects and caches all child documents matched by given {{ToParentBlockJoinQuery}} in {{OneGroup}} objects during search so it is possible to create {{GroupDocs}} with all matched child documents instead of part of them bounded by {{maxDocsPerGroup}}.
> When you specify {{maxDocsPerGroup}} new queues(I mean {{TopScoreDocCollector}}/{{TopFieldCollector}}) will be created for each group with {{maxDocsPerGroup}} objects created within each queue which could lead to redundant memory allocation in case of child documents number within group is less than {{maxDocsPerGroup}}.
> I suppose that there are many cases where you need to get all child documents matched by query so it could be nice to have ability to get top groups with all matched child documents without unnecessary memory allocation. 
> Possible solution is to pass negative {{maxDocsPerGroup}} in case when you need to get all matched child documents within each group and check {{maxDocsPerGroup}} value: if it is negative then we need to create queue with size of matched child documents number; otherwise create queue with size equals to {{maxDocsPerGroup}}. 

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