Re: explain analyze output with parallel workers - question about meaning of information for explain.depesz.com

On Mon, Nov 27, 2017 at 2:45 PM, hubert depesz lubaczewski
<depesz(at)depesz(dot)com> wrote:
> On Sat, Nov 25, 2017 at 07:08:03AM +0530, Amit Kapila wrote:
>> > For example, check step 13 in https://explain.depesz.com/s/gNBd
>> >
>> > It shows time of 3ms, but loops of 1873, so the actual time is ~ 5600ms.
>> >
>> > But with parallel execution it seems to be no longer the case.
>> >
>> > For example:
>> > https://explain.depesz.com/s/LTMp
>> > or
>> > https://explain.depesz.com/s/QHRi
>> > Should I, for explain.depesz.com, when dealing
>> > with partial* and parallel* nodes, use "loops=1" for calculation of
>> > exclusive/inclusive time? always? some other nodes?
>> >
>>
>> I am not sure what exactly inclusive or exclusive means, but for
>> parallel nodes, total stats are accumulated so you are seeing loops as
>> 'worker nodes + 1'. Now, as presumably workers run parallelly, so I
>> think the actual time will be what will be shown in the node not
>> actual time * nloops.
>
> Please check the plans:
> https://explain.depesz.com/s/gNBd (step 13)
> and https://explain.depesz.com/s/LTMp (step 3)
>
> Inclusive time is basically "loops * actual time", so for Index Scan,
> which had 1873 loops and actual time of 3.002..3.016, we got 1873
> * 3.016 = 5648.968ms.
>
> In case of parallel workers it looks like the inclusive time is
> basically the upper value from actual time.
>
> The question now is: how can I tell which nodes should use "actual_time
> * 1" and which "actual_time * loops" time?
>
> Anything "below" "Gather"?
>

I think it is "actual_time * 1" for anything below Gather.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com