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

On Tue, Nov 28, 2017 at 9:42 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Nov 28, 2017 at 2:23 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> That is wrong and I think you have hit a bug. It should be 2974 * 5 =
>> 14870 as you have seen in other cases. The problem is that during
>> rescan, we generally reinitialize the required state, but we forgot to
>> reinitialize the instrumentation related memory which is used in the
>> accumulation of stats, so changing that would fix some part of this
>> problem which is that at Parallel node, you won't see wrong values.
>> However, we also need to ensure that the per-worker details also get
>> accumulated across rescans. Attached patch should fix the problem you
>> are seeing. I think this needs some more analysis and testing to see
>> if everything works in the desired way.
>>
>> Is it possible for you to test the attached patch and see if you are
>> still seeing any unexpected values?
>
> FWIW, this looks sensible to me. Not sure if there's any good way to
> write a regression test for it.
>

I think so, but not 100% sure. I will give it a try and report back.

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