Re: wip: functions median and percentile

Dean Rasheed <dean.a.rasheed@gmail.com>

From: Dean Rasheed <dean.a.rasheed@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: Hitoshi Harada <umi.tanuki@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Greg Stark <gsstark@mit.edu>, Pavel Stehule <pavel.stehule@gmail.com>, David Fetter <david@fetter.org>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>

Date: 2010-10-11T17:55:32Z

Lists: pgsql-hackers

On 11 October 2010 18:48, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Dean Rasheed <dean.a.rasheed@gmail.com> writes:
>> On 11 October 2010 18:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Sure it would: an estimate of 30K would keep the planner from using
>>> hash aggregation.
>
>> Not if work_mem was 10MB.
>
> And?  If the memory requirement actually fits, you're in good shape.
>

Yeah but the actual memory requirement, if it uses a hash aggregate,
is over 1GB, and could easily be much higher. It's also hard to kill,
because it eats up that memory so quickly.

Regards,
Dean