"Jorge Montero" <jorge_montero@xxxxxxxxxxxxxxxxxx> writes: > The killer seems to be the row aggregation. There are about 95K > different values of sku_id in the sales table, and even the best > seller items are a very small percentage of all rows, so expecting the > aggregation to consolidate the rows 50:1 like it does in one of the > explains above is a pipe dream. I've increased statistics in sku_id > into the three digits, but results are not any better Yeah, estimating the number of distinct values from a sample of the data is a hard problem :-(. > Is there any way I can coax Postgres into making a more realistic > aggregation estimate? There's no good way in 8.3. (In CVS HEAD there's a feature to manually override the ndistinct estimate for a column.) In principle you could manually update the pg_statistic.stadistinct value for the column, but the trouble with that is the next ANALYZE will overwrite it. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
