From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Sushant Sinha <sushant354(at)gmail(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: bug in ts_rank_cd |
Date: | 2010-12-22 04:03:55 |
Message-ID: | 23981.1292990635@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Sushant Sinha <sushant354(at)gmail(dot)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
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