In case you aren't comfortable running unreleased planner patches from
pgsql-hackers, a workaround was discussed on this list recently:
http://archives.postgresql.org/pgsql-performance/2009-09/msg00036.php
On Wed, 09 Sep 2009 06:05:22 -0400, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> Kevin Kempter wrote:
>> Hi all I have a large table (>2billion rows) that's partitioned by date
>> based
>> on an epoch int value. We're running a select max(id) where id is the
>> PK. I
>> have a PK index on each of the partitions, no indexes at all on the base
>> table.
>>
>> If I hit a partition table directly I get an index scan as expected:
>
> The planner isn't smart enough to create the plan you're expecting.
> There was discussion and even a patch posted recently about that:
>
> http://archives.postgresql.org/pgsql-hackers/2009-07/msg01115.php
>
> It seems the thread petered out, but the concept seems sane.
>
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