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From "Uwe Schindler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4548) BooleanFilter should optionally pass down further restricted acceptDocs in the MUST case (and acceptDocs in general)
Date Mon, 12 Nov 2012 07:24:12 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4548?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13495131#comment-13495131
] 

Uwe Schindler commented on LUCENE-4548:
---------------------------------------

bq. RE OpenBitSet – it's not deprecated nor marked as internal. FastBitSet on the other
hand is marked as internal.

We should fix this! The problem here is, that FixedBitSet is meant as replacement and performs
better because of less checks. The problem with ChainedFilter is that it uses some features,
not yet in FixedBitSet like XORing the bitsets. The use of OpenBitSet instead of FixedBitSet
makes some optimizations inside FixedBitSet harder (e.g. FixedBitSet.or(DocIdSetIterator)
checks if the DISI is from a FixedBitSet one and then then directly ors the bits instead of
using the iterator (unless the iterator is not before the first document) - fortunately, both
OBS and FBS have the same iterator implementation).

Have you looked at my attached patch, it should fix your problems, but I don't want to commit
it now - just for testing. Or do you use FilteredQuery now for what you intended to do?
                
> BooleanFilter should optionally pass down further restricted acceptDocs in the MUST case
(and acceptDocs in general)
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-4548
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4548
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Uwe Schindler
>         Attachments: LUCENE-4548.patch
>
>
> Spin-off from dev@lao:
> {quote}
> bq. I am about to write a Filter that only operates on a set of documents that have already
passed other filter(s).  It's rather expensive, since it has to use DocValues to examine a
value and then determine if its a match.  So it scales O(n) where n is the number of documents
it must see.  The 2nd arg of getDocIdSet is Bits acceptDocs.  Unfortunately Bits doesn't have
an int iterator but I can deal with that seeing if it extends DocIdSet.
> bq. I'm looking at BooleanFilter which I want to use and I notice that it passes null
to filter.getDocIdSet for acceptDocs, and it justifies this with the following comment:
> bq. // we dont pass acceptDocs, we will filter at the end using an additional filter
> the idea of passing the already build bits for the MUST is a good idea and can be implemented
easily.
> The reason why the acceptDocs were not passed down is the new way of filter works in
Lucene 4.0 and to optimize caching. Because accept docs are the only thing that changes when
deletions are applied and filters are required to handle them separately:  whenever something
is able to cache (e.g. CachingWrapperFilter), the acceptDocs are not cached, so the underlying
filters get a null acceptDocs to produce the full bitset and the filtering is done when CachingWrapperFilter
gets the “uptodate” acceptDocs. But for this case this does not matter if the first filter
clause does not get acceptdocs, but later MUST clauses of course can get them (they are not
deletion-specific)!
> Can you open issue to optimize the MUST case (possibly MUST_NOT, too)?
> Another thing that could help here: You can stop using BooleanFilter if you can apply
the filters sequentially (only MUST clauses) by wrapping with multiple FilteredQuery: new
FilteredQuery(new FilteredQuery(originalQuery, clause1), clause2). If the DocIdSets enable
bits() and the FilteredQuery autodetection decides to use random access filters, the acceptdocs
are also passed down from the outside to the inner, removing the documents filtered out.
> {quote}
> Maybe BooleanFilter should have 2 modes (Boolean ctor argument): Passing down the acceptDocs
to every filter (for the case where Filter calculation is expensive and accept docs help to
limit the calculations) or not passing down (if the filter is cheap and the multiple acceptDocs
bit checks for every single filter is more expensive – which is then more effective, e.g.
when the Filter is only a cached bitset). The first mode would also optimize the MUST/MUST_NOT
case to pass down the further restricted acceptDocs on later filters (just like FilteredQuery
does).

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