Re: Explain buffers wrong counter with parallel plans

On Fri, Aug 3, 2018 at 2:09 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Thu, Aug 2, 2018 at 11:14 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Thu, Aug 2, 2018 at 5:41 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>> I have created three patches (a) move InstrStartParallelQuery from its
>>> original location so that we perform it just before ExecutorRun (b)
>>> patch to fix the gather stats by calling shutdown at appropriate place
>>> and allow stats collection in ExecShutdownNode (c) Probit calling
>>> ExecShutdownNode if there is a possibility of backward scans (I have
>>> done some basic tests with this patch, if we decide to proceed with
>>> it, then some more verification and testing would be required).
>>>
>>> I think we should commit first two patches as that fixes the problem
>>> being discussed in this thread and then do some additional
>>> verification for the third patch (mentioned in option c). I can
>>> understand if people want to commit the third patch before the second
>>> patch, so let me know what you guys think.
>>
>> I'm happy with the first two patches.
>>
>
> Thanks. I have pushed those two patches.
>
>> In the third one, I don't think
>> "See ExecLimit" is a good thing to put a comment like this, because
>> it's too hard to find the comment to which it refers, and because
>> future commits are likely to edit or remove that comment without
>> noticing the references to it from elsewhere. Instead I would just
>> write, in all three places, /* If we know we won't need to back up, we
>> can release resources at this point. */ or something like that.
>>
>
> Okay, I have changed the comment as per your suggestion in the
> attached patch. I will do some more testing/verification of this
> patch and will commit over the weekend or on Monday if everything is
> fine.
>

I have verified that the patch works whenever we use scrollable
cursors. Please find the attached patch with the modified commit
message. I think now it is a bit late for this minor-release and this
doesn't appear to be a blocker issue, it is better to push it after
the release.

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