Thank you Marti,
I will go with the ``reduced number of matched rows'' and naturally be waiting for postgres 9.1 expectantly.
Kind regards,
Kim
On 2011-02-15 22:13, Marti Raudsepp wrote:
On Tue, Feb 15, 2011 at 21:33, Kim A. Brandt<kimabrandt@xxxxxx> 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
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