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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-1593) Optimizations to TopScoreDocCollector and TopFieldCollector
Date Fri, 24 Apr 2009 15:49:32 GMT


Michael McCandless commented on LUCENE-1593:

bq. Actually, I think BooleanScorer need not process docs out of order? The only "out of order
ness" seems to come from how it appends each new Bucket to the head of the linked list; if
instead it appended to the tail, the collector would see docs arrive in order. I think?

I was wrong about this -- you also get "out of order ness" due to
2nd, 3rd, etc. clauses in the boolean query adding in new docs.
Re-ordering those will be costly.

But: in the initial collection of each chunk, we do know that any
docID in the queue will be less than those being visited, so this
could be a good future optimization for immediately ruling out docs
during TermScorer.  That's a larger change... eg it'd require being
able to say "I don't need exact total hit count for this search".

> 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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