[Xapian-tickets] [Xapian] #475: Multi XOR can return inconsistent results

[Xapian]

#475: Multi XOR can return inconsistent results
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 Reporter:  richard  |       Owner:  olly     
     Type:  defect   |      Status:  new      
 Priority:  normal   |   Milestone:  1.2.1    
Component:  Matcher  |     Version:  SVN trunk
 Severity:  normal   |    Keywords:           
Blockedby:           |    Platform:  All      
 Blocking:           |  
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Comment(by richard):

 I committed a fix and a testcase in r14525 for the problem of XOR children
 decaying, causing the XOR to return documents which it shouldn't have
 returned.

 However, I think there is still a problem with the weights returned from
 multi-XORs: if we have A XOR B XOR C, a document which contains A, B and C
 should be returned, and the weight should be that from A + B + C.
 However, it will actually be the weights of exactly one of A, B or C;
 worse, it's unpredictable which of those weights will be returned because
 it depends on what order the posting list tree was built in (which isn't
 under the users control).  I think to fix this there's no other option
 than implementing a MultiXorPostList - I'm not sure it's worth the effort,
 though.

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Ticket URL: <http://trac.xapian.org/ticket/475#comment:4>
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