[Xapian-tickets] [Xapian] #378: Optimise MultiAndPostList using current weight of lhs.

[Xapian]

#378: Optimise MultiAndPostList using current weight of lhs.
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 Reporter:  richard      |       Owner:  richard  
     Type:  enhancement  |      Status:  assigned 
 Priority:  normal       |   Milestone:  1.1.2    
Component:  Matcher      |     Version:  SVN trunk
 Severity:  normal       |    Keywords:           
Blockedby:               |    Platform:  All      
 Blocking:               |  
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Changes (by richard):

  * owner:  olly => richard
  * status:  new => assigned


Comment:

 Best improvement I've seen with this patch: for a search of the form "A
 AND_MAYBE B AND_MAYBE DecreasingValuePostingSource()", when requesting 300
 hits (there are around 120,000 hits matching the search), this patch more
 than doubles the speed, and results in 760 calls to check() on the
 PostingSource, instead of around 3000.  For this particular search, the
 posting source weights are large enough that the AND_MAYBE decays to a
 MultiAnd almost as soon as 300 hits have been seen.

 For the same search, when requesting fewer than 200 hits, or more than
 1000 hits, there's no easily measurable difference in speed, and the
 number of calls to check() reduces only by a couple of percent.  I've not
 yet tried it with other searches (though I've tried it with the plain
 ValuePostingSource, where it also has little effect).

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Ticket URL: <http://trac.xapian.org/ticket/378#comment:1>
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