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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-1593) Optimizations to TopScoreDocCollector and TopFieldCollector
Date Fri, 24 Apr 2009 15:44:30 GMT


Michael McCandless commented on LUCENE-1593:

bq. I tried to move to pre-populate the queue in TFC, but that proved to be impossible (unless
I missed something)

I think it should work fine, for most types, because we'd set docID
(the tie breaker) to Integer.MAX_VALUE.  No special additional if is
then required, since that entry would always compare at the bottom?

For String we should be able to use U+FFFF.

bq. So I debugged it and either the test works fine but there's a bug in MultiSearcher, or
the test does not work fine (or should be adjusted) but then we'll be changing runtime behavior
of Sort (e.g., everyone who used setSort might get undesired behavior, only in MultiSearcher).

Hmm -- good catch!  I think this is in fact a bug in MultiSearcher
(AEB is the right answer): it's failing to "break ties" (by docID)
properly.  Ie, it will not "match" what
IndexSearcher(MultiSegmentReader(...)) will do.

I think we could fix this by allowing one to pass in a docbase when
searching?  Though that's a more involved change... could you open a
new issue for this one?

bq.  I think that's wrong in the first place, we should always have predicted tests output,
since we're not involving any randomness in that code.

I agree -- let's fix it to be a deterministic test?

> Optimizations to TopScoreDocCollector and TopFieldCollector
> -----------------------------------------------------------
>                 Key: LUCENE-1593
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Shai Erera
>             Fix For: 2.9
> This is a spin-off of LUCENE-1575 and proposes to optimize TSDC and TFC code to remove
unnecessary checks. The plan is:
> # Ensure that IndexSearcher returns segements in increasing doc Id order, instead of
> # Change TSDC and TFC's code to not use the doc id as a tie breaker. New docs will always
have larger ids and therefore cannot compete.
> # Pre-populate HitQueue with sentinel values in TSDC (score = Float.NEG_INF) and remove
the check if reusableSD == null.
> # Also move to use "changing top" and then call adjustTop(), in case we update the queue.
> # some methods in Sort explicitly add SortField.FIELD_DOC as a "tie breaker" for the
last SortField. But, doing so should not be necessary (since we already break ties by docID),
and is in fact less efficient (once the above optimization is in).
> # Investigate PQ - can we deprecate insert() and have only insertWithOverflow()? Add
a addDummyObjects method which will populate the queue without "arranging" it, just store
the objects in the array (this can be used to pre-populate sentinel values)?
> I will post a patch as well as some perf measurements as soon as I have them.

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