bug in ts_rank_cd
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
Attachments:
tsrankbugfix.patchtext/x-patch; charset=UTF-8; name=tsrankbugfix.patchDownload
--- postgresql-9.0.0/src/backend/utils/adt/tsrank.c 2010-01-02 22:27:55.000000000 +0530
+++ postgres-9.0.0-tsrankbugfix/src/backend/utils/adt/tsrank.c 2010-12-21 18:39:57.000000000 +0530
@@ -551,7 +551,7 @@
memset(qr->operandexist, 0, sizeof(bool) * qr->query->size);
ext->p = 0x7fffffff;
- ext->q = 0;
+ ext->q = -1;
ptr = doc + ext->pos;
/* find upper bound of cover from current position, move up */
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
Show quoted text
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 sayselect ts_rank_cd(to_tsvector('english', 'abc sdd'),
plainto_tsquery('english', 'abc'));
ts_rank_cd
------------
0but 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