On Thu, 2006-06-15 at 14:21, John Vincent wrote: > On 6/15/06, Mark Lewis <mark.lewis@xxxxxxxx> 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.
