Thread

1. bug in ts_rank_cd

   Sushant Sinha <sushant354@gmail.com> — 2010-12-21T13:38:35Z

   MY PREV EMAIL HAD A PROBLEM. Please reply to this one
   ======================================================
   
   There is a bug in ts_rank_cd. It does not correctly give rank when the
   query lexeme is the first one in the tsvector.
   
   Example:
   
   select ts_rank_cd(to_tsvector('english', 'abc sdd'),
   plainto_tsquery('english', 'abc'));   
    ts_rank_cd 
   ------------
             0
   
   select ts_rank_cd(to_tsvector('english', 'bcg abc sdd'),
   plainto_tsquery('english', 'abc'));
    ts_rank_cd 
   ------------
           0.1
   
   The problem is that the Cover finding algorithm ignores the lexeme at
   the 0th position, I have attached a patch which fixes it. After the
   patch the result is fine.
   
   select ts_rank_cd(to_tsvector('english', 'abc sdd'), plainto_tsquery(
   'english', 'abc'));
    ts_rank_cd 
   ------------
           0.1
   
   

2. Re: bug in ts_rank_cd

   Tom Lane <tgl@sss.pgh.pa.us> — 2010-12-22T04:03:55Z

   Sushant Sinha <sushant354@gmail.com> writes:
   > There is a bug in ts_rank_cd. It does not correctly give rank when the
   > query lexeme is the first one in the tsvector.
   
   Hmm ... I cannot reproduce the behavior you're complaining of.
   You say
   
   > select ts_rank_cd(to_tsvector('english', 'abc sdd'),
   > plainto_tsquery('english', 'abc'));   
   >  ts_rank_cd 
   > ------------
   >           0
   
   but I get
   
   regression=# select ts_rank_cd(to_tsvector('english', 'abc sdd'),
   regression(# plainto_tsquery('english', 'abc'));   
    ts_rank_cd 
   ------------
           0.1
   (1 row)
   
   > The problem is that the Cover finding algorithm ignores the lexeme at
   > the 0th position,
   
   As far as I can tell, there is no "0th position" --- tsvector counts
   positions from one.  The only way to see pos == 0 in the input to
   Cover() is if the tsvector has been stripped of position information.
   ts_rank_cd is documented to return 0 in that situation.  Your patch
   would have the effect of causing it to return some nonzero, but quite
   bogus, ranking.
   
   			regards, tom lane
   
   

3. Re: bug in ts_rank_cd

   Sushant Sinha <sushant354@gmail.com> — 2010-12-22T12:44:43Z

   Sorry for sounding the false alarm. I was not running the vanilla
   postgres and that is why I was seeing that problem. Should have checked
   with the vanilla one.
   
   -Sushant
   
   On Tue, 2010-12-21 at 23:03 -0500, Tom Lane wrote:
   > Sushant Sinha <sushant354@gmail.com> writes:
   > > There is a bug in ts_rank_cd. It does not correctly give rank when the
   > > query lexeme is the first one in the tsvector.
   > 
   > Hmm ... I cannot reproduce the behavior you're complaining of.
   > You say
   > 
   > > select ts_rank_cd(to_tsvector('english', 'abc sdd'),
   > > plainto_tsquery('english', 'abc'));   
   > >  ts_rank_cd 
   > > ------------
   > >           0
   > 
   > but I get
   > 
   > regression=# select ts_rank_cd(to_tsvector('english', 'abc sdd'),
   > regression(# plainto_tsquery('english', 'abc'));   
   >  ts_rank_cd 
   > ------------
   >         0.1
   > (1 row)
   > 
   > > The problem is that the Cover finding algorithm ignores the lexeme at
   > > the 0th position,
   > 
   > As far as I can tell, there is no "0th position" --- tsvector counts
   > positions from one.  The only way to see pos == 0 in the input to
   > Cover() is if the tsvector has been stripped of position information.
   > ts_rank_cd is documented to return 0 in that situation.  Your patch
   > would have the effect of causing it to return some nonzero, but quite
   > bogus, ranking.
   > 
   > 			regards, tom lane