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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1593) Optimizations to TopScoreDocCollector and TopFieldCollector
Date Thu, 30 Apr 2009 20:43:30 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12704785#action_12704785
] 

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

bq. add an API to Collector for it to declare if it can handle out-of-order collection, and
then ask for the right Scorer.

Maybe instead add docsOrderSupportedMode() which returns IN_ORDER, OUT_OF_ORDER, DONT_CARE?
I.e., instead of a boolean allow a Collector to say "I don't really care" (like Mike has pointed
out, I think, somewhere above) and let the Scorer creation code decide which one to create
in case it knows any better. I.e., if we know that BS performs better than BS2, and we get
a Collector saying DONT_CARE, we can always return BS.
Unless we assume that OUT_OF_ORDER covers DONT_CARE either, in which case we can leave it
as returning boolean and document that if a Collector can support OUT_OF_ORDER, it should
always say so, giving the Scorer creator code a chance to decide what is the best Scorer to
return.

In IndexSearcher we can then:
# Where Collector is given as argument, ask it if it about orderness and create the appropriate
Scorer.
# Where we create our own Collector (i.e. TFC and TSDC) decide on our own what is better.
Maybe always ask out-of-order? That way a Query which doesn't only supports in-order without
any optimization for out-of-order can return that in-order collector. I didn't think of it
initially, but Mike is right - every in-order scorer is also an out-of-order scorer, so this
should be fine.

I like the approach of deprecating Weight and creating an abstract class, though that requires
deprecating Searchable and creating an AbstractSearchable as well. Weight can be wrapped with
an AbstractWeightWrapper and passed to the AbstractWeight methods (much like we do with AbstractHitCollector
from LUCENE-1575), defaulting its scorer(inOrder) method to call scorer()?

This I guess should be done in the scope of that issue, or I revert the changes done to Query
(adding scoresDocsInOrder()), but keep those done to TFC and TSDC, and make that optimization
in a different issue, which will handle Weight/Searchable and the rest of the changes proposed
here?

> 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, 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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