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https://issues.apache.org/jira/browse/LUCENE-1518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12704597#action_12704597
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Shai Erera commented on LUCENE-1518:
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bq. Wrapping with CSQ is just adding anothe layer between Lucene search
machinery and Filter, making these optimizations harder.
Right. But making Filter sub-class Query and check in BQ 'if (query instanceof
Filter) { Filter f = (Filter) query)' is not going to improve anything. It adds
instanceof and casting, and I'd think those are more expensive than wrapping a
Filter with CSQ and returning an appropriate Scorer, which will use the Filter
in its next() and skipTo() calls.
bq. On the other hand, I must accept, conceptually FIter and Query are "the
same", supporting together following options
I think that if we allow BooleanClause to implement a Weight(IndexReader) (just
like Query) we'll be one more step closer to that goal? BQ uses this method to
construct BooleanWeight, only today it calls clause.getQuery().createWeight().
Instead it could do clause.getWeight, and if the BooleanClause holds a Filter
it will return a FilterWeight, otherwise delegate that call to the contained
Query.
Regarding pure ranked, CSQ is really what we need, no?
So how about the following:
# Add add(Filter, Occur) to BooleanClause.
# Add weight(Searcher) to BooleanClause.
# Create a FilterWeight which wraps a Filter and provide a Scorer
implementation with a constant score. (This does not handle the "no scoring"
mode, unless "no scoring" can be achieved with score=0.0f, while constant is
any other value, defaulting to 1.0f).
# Add isRandomAccess to Filter.
# Create a RandomAccessFilter which extends Filter and defines an additional
seek(target) method.
# Add asRandomAccessFilter() to Filter, which will materialize that Filter into
memory, or into another RandomAccess data structure (e.g. keeping it on disk
but still provide random access to it, even if not very efficient) and return a
RandomAccessFilter type, which will implement seek(target) and possibly
override next() and skipTo(), but still use whatever other methods this Filter
declares.
#* I think we should default it to throw UOE providing that we document that
isRandomAccess should first be called.
I'm thinking out loud just like you, so I hope my stuff makes sense :).
> Merge Query and Filter classes
> ------------------------------
>
> Key: LUCENE-1518
> URL: https://issues.apache.org/jira/browse/LUCENE-1518
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.4
> Reporter: Uwe Schindler
> Fix For: 2.9
>
> Attachments: LUCENE-1518.patch
>
>
> This issue presents a patch, that merges Queries and Filters in a way, that
> the new Filter class extends Query. This would make it possible, to use every
> filter as a query.
> The new abstract filter class would contain all methods of
> ConstantScoreQuery, deprecate ConstantScoreQuery. If somebody implements the
> Filter's getDocIdSet()/bits() methods he has nothing more to do, he could
> just use the filter as a normal query.
> I do not want to completely convert Filters to ConstantScoreQueries. The idea
> is to combine Queries and Filters in such a way, that every Filter can
> automatically be used at all places where a Query can be used (e.g. also
> alone a search query without any other constraint). For that, the abstract
> Query methods must be implemented and return a "default" weight for Filters
> which is the current ConstantScore Logic. If the filter is used as a real
> filter (where the API wants a Filter), the getDocIdSet part could be directly
> used, the weight is useless (as it is currently, too). The constant score
> default implementation is only used when the Filter is used as a Query (e.g.
> as direct parameter to Searcher.search()). For the special case of
> BooleanQueries combining Filters and Queries the idea is, to optimize the
> BooleanQuery logic in such a way, that it detects if a BooleanClause is a
> Filter (using instanceof) and then directly uses the Filter API and not take
> the burden of the ConstantScoreQuery (see LUCENE-1345).
> Here some ideas how to implement Searcher.search() with Query and Filter:
> - User runs Searcher.search() using a Filter as the only parameter. As every
> Filter is also a ConstantScoreQuery, the query can be executed and returns
> score 1.0 for all matching documents.
> - User runs Searcher.search() using a Query as the only parameter: No change,
> all is the same as before
> - User runs Searcher.search() using a BooleanQuery as parameter: If the
> BooleanQuery does not contain a Query that is subclass of Filter (the new
> Filter) everything as usual. If the BooleanQuery only contains exactly one
> Filter and nothing else the Filter is used as a constant score query. If
> BooleanQuery contains clauses with Queries and Filters the new algorithm
> could be used: The queries are executed and the results filtered with the
> filters.
> For the user this has the main advantage: That he can construct his query
> using a simplified API without thinking about Filters oder Queries, you can
> just combine clauses together. The scorer/weight logic then identifies the
> cases to use the filter or the query weight API. Just like the query
> optimizer of a RDB.
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