On 17 August 2018 at 06:52, Robert Haas <
robertmhaas@gmail.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