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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1536) if a filter can support random access API, we should use it
Date Wed, 07 Apr 2010 17:36:34 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854612#action_12854612
] 

Michael McCandless commented on LUCENE-1536:
--------------------------------------------

With flex, you can now get the deleted docs from a reader (returns a Bits, yet another interface
for bitsets), and, Docs/AndPositionsEnums require that you pass in the skipDocs.  Ie they
no longer skip deleted docs by default.

I think this makes this issue quite a bit simpler?  EG OpenBitSets implements Bits (as of
flex landing), so... we just need a way to pass this Bits down to the low level scorers that
actually pull a postings list.  But, we should only do this if the filter is not sparse.

Also: the filter must be inverted, and, ORd with the deleted docs.

This can result in enormous perf gains for searches doing filtering where the filter is relatively
static (can be cached & shared across searches).

> if a filter can support random access API, we should use it
> -----------------------------------------------------------
>
>                 Key: LUCENE-1536
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1536
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>    Affects Versions: 2.4
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 3.1
>
>         Attachments: LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch, LUCENE-1536.patch,
LUCENE-1536.patch
>
>
> I ran some performance tests, comparing applying a filter via
> random-access API instead of current trunk's iterator API.
> This was inspired by LUCENE-1476, where we realized deletions should
> really be implemented just like a filter, but then in testing found
> that switching deletions to iterator was a very sizable performance
> hit.
> Some notes on the test:
>   * Index is first 2M docs of Wikipedia.  Test machine is Mac OS X
>     10.5.6, quad core Intel CPU, 6 GB RAM, java 1.6.0_07-b06-153.
>   * I test across multiple queries.  1-X means an OR query, eg 1-4
>     means 1 OR 2 OR 3 OR 4, whereas +1-4 is an AND query, ie 1 AND 2
>     AND 3 AND 4.  "u s" means "united states" (phrase search).
>   * I test with multiple filter densities (0, 1, 2, 5, 10, 25, 75, 90,
>     95, 98, 99, 99.99999 (filter is non-null but all bits are set),
>     100 (filter=null, control)).
>   * Method high means I use random-access filter API in
>     IndexSearcher's main loop.  Method low means I use random-access
>     filter API down in SegmentTermDocs (just like deleted docs
>     today).
>   * Baseline (QPS) is current trunk, where filter is applied as iterator up
>     "high" (ie in IndexSearcher's search loop).

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