From: | Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> |
---|---|
To: | Vikul Khosla <vkhosla(at)gridsolv(dot)com> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Indexes on low cardinality columns |
Date: | 2009-10-19 13:59:43 |
Message-ID: | 4ADC70CF.8040600@cheapcomplexdevices.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-performance |
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
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2009-10-19 16:01:17 | Re: Calculation of unused columns |
Previous Message | Grzegorz Jaśkiewicz | 2009-10-19 13:46:58 | Re: Known Bottlenecks |