Re: Parallel Select query performance and shared buffers

On Wed, Dec 4, 2013 at 12:57 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> As a quick side, we also repeated the same experiment on an EC2 instance
>> with 16 CPU cores, and found that the scale out behavior became worse there.
>> (We also tried increasing the shared_buffers to 30 GB. This change
>> completely solved the scaling out problem on this instance type, but hurt
>> our performance on the hi1.4xlarge instances.)
>
> Instead of 30GB, you can try with lesser value, but it should be close
> to your data size.

The OS cache should have provided a similar function.

In fact, larger shared buffers shouldn't have made a difference if the
main I/O pattern are sequential scans, because they use a ring buffer.

Can we have the explain analyze of those queries, postgres
configuration, perhaps vmstat output during execution?