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From Chuck Williams <>
Subject Re: Query.combine()
Date Tue, 30 May 2006 21:55:59 GMT
If I understand what you are saying, unfortunately it will not work. 
The issue is that rewrite() needs to access the index.  E.g., a* or [a
TO d] rewrite to disjunctions of all terms that exist in the index that
match, respectively, the prefix or range.  To determine this set of
terms it is necessary to access each index.  rewrite() does the
expansion for the separate subindexes, and then combine() builds the
larger disjunction that captures all terms for a single query that will
work against any index.  Unless all your subindexes have precisely the
same terms, I don't see how you could avoid the hops to access each
subindex for rewrite().

There is another place I would suggest looking, though. 
ParallelMultiSearcher needs to access the df's for each term and sum
them in order to compute the Weight for the combined query.  I don't
believe anybody has benchmarked this, but I've always believed that
caching the df's on the central server would be a significant benefit.


Joe R wrote on 05/30/2006 11:32 AM:
> Hello,
> I'm trying to write a MultiSearcher/ParallelMultiSearcher variation that uses
> JMS to talk to its subordinate Searchers.  While running through MultiSearcher
> to see where I can save some cycles or network hops, I came across
> Query.combine().  It's called from MultiSearcher.rewrite() (as you know) but
> seems to be there only to allow for different Searcher implementations in
> MultiSearcher's subordinate Searchers.  So, am I correct in assuming that, if I
> use the same Searcher to query every subordinate index, I can save myself a
> network hop by rewriting/combine()ing the Query once, in the JMS MultiSearcher?
> Every other time I thought I'd found an optimization it turned out to be
> written the way it was for a reason.  I'm wondering if that's going to be the
> case here, too -- hence the question.
> Thanks for the help.
> -joe
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