Re: Optimizer internals

On Thu, 2006-06-15 at 14:21, John Vincent wrote:
> On 6/15/06, Mark Lewis <mark(dot)lewis(at)mir3(dot)com> wrote:
> Unfortunately SUM is in the same boat as COUNT; in order for
> it to
> return a meaningful result it must inspect visibility
> information for
> all of the rows.
>
> -- Mark
>
> We'll this is interesting news to say the least. We went with
> PostgreSQL for our warehouse because we needed the advanced features
> that MySQL didn't have at the time (views/sprocs).
>
> It sounds like we almost need another fact table for the places that
> we do SUM (which is not a problem just an additional map. If I'm
> interpreting this all correctly, we can't force PG to bypass a
> sequence scan even if we know our data is stable because of the MVCC
> aspect. In our case, as with most warehouses (except those that do
> rolling loads during the day), we only write data to it for about 5
> hours at night in batch.
>
> Any suggestions? FYI the original question wasn't meant as a poke at
> comparing PG to MySQL to DB2. I'm not making an yvalue judgements
> either way. I'm just trying to understand how we can use it the best
> way possible.
>
> If anyone from the bizgres team is watching, have they done any work
> in this area?

This might help:

http://jonathangardner.net/PostgreSQL/materialized_views/matviews.html

Since you're doing a data warehouse, I would think materialized views
would be a natural addition anyway.