[Xapian-tickets] [Xapian] #387: Optimisation for a filter term matching all documents

[Xapian]

#387: Optimisation for a filter term matching all documents
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 Reporter:  olly         |       Owner:  olly
     Type:  enhancement  |      Status:  new 
 Priority:  normal       |   Milestone:      
Component:  Matcher      |     Version:      
 Severity:  normal       |   Blockedby:      
 Platform:  All          |    Blocking:      
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 If a term matches all documents (i.e. termfreq == doccount) and we don't
 want weight information for it (e.g. we're using {{{OP_FILTER}}} or
 {{{BoolWeight}}}) then we don't actually need to look at its postings at
 all - we can just treat it as {{{QueryMatchAll}}}.

 This might not seem very useful, but if it worked at the submatch level,
 it would allow database selection from within the query string using
 "database:1" to filter by XDB1, or something like that.

 This would also naturally extend to optimising a term which matches
 exactly a contiguous range of documents if we start storing the highest
 and lowest document id a term indexes, which we plan to do at some point,
 since if (termfreq = highest_docid - lowest_docid + 1) then we know
 exactly the documents the term indexes without looking at the postings.

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Ticket URL: <http://trac.xapian.org/ticket/387>
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