Re: Parallel Select query performance and shared buffers

On Wed, Dec 4, 2013 at 1:54 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> On 2013-12-04 18:43:35 +0200, Metin Doslu wrote:
>> > I'd strongly suggest doing a "perf record -g -a <wait a bit, ctrl-c>;
>> > perf report" run to check what's eating up the time.
>>
>> Here is one example:
>>
>> +  38.87%   swapper  [kernel.kallsyms]   [k] hypercall_page
>> +   9.32%  postgres  [kernel.kallsyms]   [k] hypercall_page
>> +   6.80%  postgres  [kernel.kallsyms]   [k] xen_set_pte_at
>
> All that time is spent in your virtualization solution. One thing to try
> is to look on the host system, sometimes profiles there can be more
> meaningful.

You cannot profile the host on EC2.

You could try HVM. I've noticed it fare better  under heavy CPU load,
and it's not fully-HVM (it still uses paravirtualized network and
I/O).