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From "Michael McCandless (JIRA)" <>
Subject [jira] Commented: (LUCENE-1593) Optimizations to TopScoreDocCollector and TopFieldCollector
Date Mon, 04 May 2009 21:58:30 GMT


Michael McCandless commented on LUCENE-1593:

Shai your summary of what needs to be done looks right.  But:
shouldn't we do the interface -> abstract class migration (of Weight &
Searchable) under a separate issue?  Ie, under that issue no real
functional change to Lucene is happening.  Then in this issue we can
make the optimizations?

I just ran a quick perf test (best of 5 runs, Linux, JDK 1.6) of the
query 1 OR 2 on a large Wikipedia index.  Using BS instead of BS2
gives a 27% speedup (2.2 QPS -> 2.8).  I'd really like for Lucene to
be able to use BS automatically when it can.  In fact, I think we should
move more scorers to out-of-order, if we can get these kinds of
performance gains.

These changes go beyond that, though, and also enable a separate
optimization whereby the Collector knows it doesn't have to break ties
by docID.  TFC would then use that to gain performance for all in-order

bq. Some of these changes were discussed elsewhere already, e.g. deprecating Weight and Searchable
and make them abstract classes for easier such changes in the future.

In fact I think most of the work above is for this (and not the
optimizations), and I think migration from interfaces -> abstract
classes is important (for 2.9).

> Optimizations to TopScoreDocCollector and TopFieldCollector
> -----------------------------------------------------------
>                 Key: LUCENE-1593
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Shai Erera
>             Fix For: 2.9
>         Attachments: LUCENE-1593.patch, LUCENE-1593.patch,
> 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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