Index used incorrectly with regular expressions on 7.4.6

Index is used incorrectly if constant part of the string ends with \d,
probably also with other escapes.

foo=# explain select count(*) from loc where url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+'; QUERY PLAN

Aggregate (cost=3.46..3.46 rows=1 width=0)
-> Index Scan using url_index on loc (cost=0.00..3.46 rows=1 width=0)
Index Cond: ((url >=
'http://www.7-eleven.com/newsroom/articles.asp?p=d'::text) AND
(url < 'http://www.7-eleven.com/newsroom/articles.asp?p=e'::text))
Filter: (url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+'::text)
(4 rows)
foo=# select count(*) from loc where url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';
count
-------
0
(1 row)

foo=# set enable_indexscan = off;
SET
foo=# explain select count(*) from loc where url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';
QUERY PLAN
Aggregate (cost=3056.41..3056.41 rows=1 width=0)
-> Seq Scan on loc (cost=0.00..3056.40 rows=1 width=0)
Filter: (url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+'::text)
(3 rows)

foo=# select count(*) from loc where url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';
count
-------
281
(1 row)

--
Antti Salmela