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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1593) Optimizations to TopScoreDocCollector and TopFieldCollector
Date Wed, 29 Apr 2009 14:46:30 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12704136#action_12704136
] 

Shai Erera commented on LUCENE-1593:
------------------------------------

Hmmm .. I think DISI.start() breaks back-compat, since if we optimize the scorers to not check
if they're initializes in next() and skipTo(), then you'll get NPE (or something else will
happen). Even if we fix IndexSearcher to call start(), someone may still iterate on a Scorer
privately, or in a custom code (I know I do).

I think this change should go into 3.0 as well, as it's a wider change than I though initially.
It affects more than just BS2, but all of its internal classes, as well as some other Scorers.
Also, I see in several scorers different TODOs to get rid of that init() check in next() and
skipTo(), and so this smells like a wider change.

Since it breaks back-compat and the change will affect not just BS/BS2, I prefer to leave
that optimization out of them for now, and fix it all in 3.0, including the other scorers.

So we have two issues for 3.0:
# Introduce start() in DISI and change all the classes that extend DISI to take advantage
of it, as well as all the code that uses DISI to call start().
# Introduce topScorer() to Weight, and take advantage of it where it makes sense (currently
we know of BW), and change all the code that calls scorer.score(Collector) to request a topScorer()
from Weight.

Since Scorer extends DISI these often look to be the same usage, but I think they are different,
with different use cases. What do you think?

> Optimizations to TopScoreDocCollector and TopFieldCollector
> -----------------------------------------------------------
>
>                 Key: LUCENE-1593
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1593
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>            Reporter: Shai Erera
>             Fix For: 2.9
>
>         Attachments: LUCENE-1593.patch, PerfTest.java
>
>
> 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
numDocs().
> # 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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