On 11 October 2010 18:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Dean Rasheed <dean.a.rasheed@gmail.com> writes:
>> The estimate of 200 x 8K is below work_mem, so it uses a hash
>> aggregate. In reality, each tuplesort allocates around 30K initially,
>> so it very quickly uses over 1GB. A better estimate for the aggregate
>> wouldn't improve this situation much.
>
> Sure it would: an estimate of 30K would keep the planner from using
> hash aggregation.
>
Not if work_mem was 10MB.
Regards,
Dean
