Re: index on lower(column) is very slow

valerian <valerian2(at)hotpop(dot)com> writes:

> I just realized that I was behind by one release, so I upgraded to pgsql
> 7.3.2, then added some more random data (18000 rows in the table now)
> and ran 'VACUUM FULL ANALYZE' again. Here's the subsequent results:
>
> test=> EXPLAIN SELECT id, password FROM test WHERE LOWER(email) = 'pwcm6(at)pgaxd6hhuteforp966cz';
> QUERY PLAN
> ----------------------------------------------------------------------------------
> Index Scan using test_email_lc_idx on test (cost=0.00..292.25 rows=91 width=16)
> Index Cond: (lower((email)::text) = 'pwcm6(at)pgaxd6hhuteforp966cz'::text)
> (2 rows)

Try "explain analyze" which will actually run the query and print timing
information.

Also, note that the number of records returned is probably a big factor here.
The case-sensitive version is only returning 1 record whereas postgres expects
the case=insensitive version to return 91 records. Try the case-sensitive
version on a value that has a comparable number of records to for a better
test.

--
greg