Peng Cheng created LUCENE-5409:
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             Summary: ToParentBlockJoinCollector.getTopGroups returns empty 
Groups
                 Key: LUCENE-5409
                 URL: https://issues.apache.org/jira/browse/LUCENE-5409
             Project: Lucene - Core
          Issue Type: Bug
          Components: core/search
    Affects Versions: 4.6
         Environment: Ubuntu 12.04
            Reporter: Peng Cheng
            Priority: Critical
             Fix For: 4.7


In the scorer generation stage, the ToParentBlockJoinCollector will 
automatically rewrite all the associated ToParentBlockJoinQuery (and their 
subqueries), and save them into its in-memory Look-up table, namely joinQueryID 
(see enroll() method for detail). Unfortunately, in the getTopGroups method, 
the new ToParentBlockJoinQuery parameter is not rewritten (at least users are 
not expected to do so). When the new one is searched in the old lookup table 
(considering the impact of rewrite() on hashCode()), the result (namely _slot) 
will always fail and eventually end up with a topGroup collection consisting of 
only empty groups (their hitCounts are guaranteed to be zero).

An easy fix would be to rewrite the original BlockJoinQuery before invoking 
getTopGroups method. However, the computational cost of this is not optimal. A 
better but slightly more complex solution would be to save unrewrited Queries 
into the lookup table.



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