Re: Indexes on low cardinality columns

If the table can be clustered on that column, I suspect
it'd be a nice case for the grouped index tuples patch
http://community.enterprisedb.com/git/

Actually, simply clustering on that column might give
major speedups anyway.

Vikul Khosla wrote:
> Folks,
>
> We have just migrated from Oracle to PG.
>
> We have a database that has approx 3 mil rows and one of the columns has
> a cardinality
> of only 0.1% (3000 unique values).
>
> We have to issue several queries that use this low cardinality column in
> a WHERE clause
> as well as see this column participating in JOINS (ouch!).
>
> A regular B-Tree index has been created on these columns.
>
> In Oracle, we replaced the B-Tree Indexes with Bitmap indexes and saw
> performance go
> through the roof. I know Postgres does not have Bitmap indexes,
> but is there a reasonable alternative to boost performance in situations
> where low cardinality
> columns are involved ?
>
> I dont have the option of changing schemas - so please dont go there :)
>
> TIA,
> VK