On 17 August 2018 at 06:52, Robert Haas <robertmh...@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 -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
