On Fri, 2007-10-26 at 16:37 -0400, Pablo Alcaraz wrote: > I executed 2 equivalents queries. The first one uses a union structure. > The second uses a partitioned table. The tables are the same with 30 > millions of rows each one and the returned rows are the same. > > But the union query perform faster than the partitioned query. > > My question is: why? :) The two queries are equivalent but they have different execution plans. The UNION query has explicit GROUP BY operations within it. We do not currently perform a push-down operation onto the individual partitions. This results in more data copying as well as requiring a single very large sort, rather than lots of small ones. That is probably enough to allow it to perform the sort in memory rather than on-disk, thus allowing a considerable speed-up. This is on my list of requirements for further partitioning improvements in 8.4 or beyond. -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
