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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-2190) CustomScoreQuery (function query) is broken (due to per-segment searching)
Date Sat, 20 Feb 2010 13:17:27 GMT


Michael McCandless commented on LUCENE-2190:

bq. Adding setNextReader to CustomScoreQuery makes the Query itsself stateful. This breaks
when using together with e.g. ParallelMultiSearcher.

Ugh, you're right.  Passing the current IR to customScore method isn't great because then
you have to a check per call (per doc scored) to detect a switch to a new reader.

bq. but when we change to per-segment rewrite (as Mike plans) 

I'm not quite "planning" that ;)  I was mulling it... because it's somewhat inefficient now
that an MTQ uses the multi terms enum instead of doing it per segment.  But: this is only
done for the BQ rewrite, which is only done when the number of terms is smallish (with AUTO
default rewrite), so I think in practice the actual cost is low?

> CustomScoreQuery (function query) is broken (due to per-segment searching)
> --------------------------------------------------------------------------
>                 Key: LUCENE-2190
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Search
>    Affects Versions: 2.9, 2.9.1, 3.0, 3.0.1, 3.1
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 2.9.2, 3.0.1, 3.1
>         Attachments: LUCENE-2190.patch
> Spinoff from here:
> With the cutover to per-segment searching, CustomScoreQuery is not really usable anymore,
because the per-doc custom scoring method (customScore) receives a per-segment docID, yet
there is no way to figure out which segment you are currently searching.
> I think to fix this we must also notify the subclass whenever a new segment is switched
to.  I think if we copy Collector.setNextReader, that would be sufficient.  It would by default
do nothing in CustomScoreQuery, but a subclass could override.

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