bug in ts_rank_cd

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

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