On Tue, Feb 15, 2011 at 21:33, Kim A. Brandt <kimabra...@gmx.de> wrote: > removing the ORDER BY worked. But I am afraid to ask this. How can I order > by partition? It seams that the planner has picked a random(!?) order of > partition to select from. The returned records, from the selected partition, > are correctly sorted bythe index though.
If a single query accesses more than one partition, PostgreSQL currently cannot read the values in index-sorted order. Hence with ORDER BY and LIMIT, PostgreSQL cannot return *any* results before it has read all matching rows and then sorted them. Adding a LIMIT doesn't help much. Your only bet is to reduce the number of matched rows, or make sure that you only access a single partition. Increasing work_mem may speed up the sort step if you're hitting the disk (EXPLAIN ANALYZE VERBOSE will tell you whether that's the case). This will change in PostgreSQL 9.1 which has a new Merge Append plan node. Regards, Marti -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
