Re: FailedAssertion on partprune

> On Aug 17, 2018, at 2:49 AM, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>
> On 17 August 2018 at 06:52, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I don't know whether there's actually a defect here any more. I was
>> trying to dispel some perceived confusion on the part of David and Tom
>> about what this code was trying to accomplish, but the fact that the
>> code caused some confusion does not necessarily mean that there's
>> anything wrong with it. On the other hand, perhaps it does have
>> functional deficiencies, or perhaps the comments need work. Or maybe
>> this code is fine taken in isolation but there are still problems in
>> how it interacts with partition pruning. Let's start by deciding what
>> we think the problems are, and then we can decide who should fix them.
>
> I think Tom and I both agree that the plan mentioned in [1] and [2] is
> not quite as optimal as it could be. The investigation I did in [3]
> highlights where this got broken and the reason why it got broken.
>
> Tom removed the offending Assert() in 59ef49d26d2, but mentioned
> there's no test case which tries to ensure having a partitioned table
> as an Append child works correctly. I agree that it would be nice to
> have a test for this, but I did try a couple of times to come up with
> a test case to do this, but I was unable to come up with anything
> suitable compact for the regression tests, and even at that, given how
> difficult it is to get a plan into this shape, I didn't hold up much
> hope of the test's plan remaining stable. Tom seems to agree with this
> as he mentioned in [2].
>
> I think the best path forward is if you (Robert) could verify the
> behaviour that I mentioned in [3] is expected behaviour, if it is then
> perhaps the path forward is for me to try harder to write a compact
> test for this, but if you discover that the behaviour is unexpected
> then I think the best course of action is to fix it to properly
> flatten the
> Append which will mean there's no need for a test case, and perhaps
> the Assert that was removed can be put back again.
>
> [1] https://www.postgresql.org/message-id/CAKJS1f9MQd5ntg6xXg7jJe0jB_bWvCDRmaH6yNzZGF%2BTVa5M%3DA%40mail.gmail.com
> [2] https://www.postgresql.org/message-id/8600.1533765148%40sss.pgh.pa.us
> [3] https://www.postgresql.org/message-id/CAKJS1f_j9BSJ7svDF7uid6EMm%2Bfu%2BcAhonZ7hcqiYU4ssv3rtg%40mail.gmail.com <https://www.postgresql.org/message-id/CAKJS1f_j9BSJ7svDF7uid6EMm+fu+cAhonZ7hcqiYU4ssv3rtg@mail.gmail.com>

On behalf of the RMT, I just want to make sure this keeps moving along.
It sounds like the next step is for Robert to verify that [3] is the expected
behavior and then David can decide what to do from there.

Thanks!

Jonathan