[Xapian-tickets] [Xapian] #340: PostingSource subclasses cannot signal a change in their maxweight

[Xapian]

#340: PostingSource subclasses cannot signal a change in their maxweight
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 Reporter:  richard      |        Owner:  olly     
     Type:  defect       |       Status:  new      
 Priority:  normal       |    Milestone:  1.1.1    
Component:  Library API  |      Version:  SVN trunk
 Severity:  normal       |   Resolution:           
 Keywords:               |    Blockedby:           
 Platform:  All          |     Blocking:           
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Comment(by richard):

 If I recall correctly, the worry with this scheme was that cumulative
 rounding errors due to passing the matcher a series of small changes in
 the maxweight could have the effect of causing the matcher to optimise
 prematurely.  This is probably unlikely to occur often, and, indeed, can
 probably occur even with the current setup, but the cumulative effect
 could make it likely enough to be a problem that we need to deal with it.

 Olly was looking into ways to control the rounding direction, which would
 allow us to ensure that the rounding always happened in such a way that
 invalid optimisations didn't occur.  However, this only seems to be
 possible on a process-global level, which isn't appropriate for a library.

 My best idea so far is just to add an epsilon whenever modifying the
 maxweight, to ensure that the rounding is in the right direction.

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Ticket URL: <http://trac.xapian.org/ticket/340#comment:10>
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