Re: pg_dump versus hash partitioning

On Wed, Feb 1, 2023 at 4:44 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> This is a misrepresentation of Tom's words. It isn't actually
> self-evident what "we end up with all of the same objects, each
> defined in the same way, and that all of the tables end up with all
> the same contents that they had before" actually means here, in
> general. Tom's main concern seems to be just that -- the ambiguity
> itself.

As far as I can see, Tom didn't admit that there was any ambiguity. He
just said that I was advocating for wrong behavior for the sake of
performance. I don't think that is what I was doing. I also don't
really think Tom thinks that that is what I was doing. But it is what
he said I was doing.

I do agree with you that the ambiguity is the root of the issue. I
mean, if we can't put the rows back into the same partitions where
they were before, does the user care about that, or do they only care
that the rows end up in some partition of the toplevel partitioned
table? I think that there's no single definition of correctness that
is the only defensible one here, and we can't know which one the user
wants a priori. I also think that they can care which one they're
getting, and thus I think that changing the default in a minor release
is a bad plan. Tom, as I understand it, is arguing that the
--load-via-partition-root behavior has negligible downsides and is
almost categorically better than the current default behavior, and
thus making that the new default in some or all situations in a minor
release is totally fine.

--
Robert Haas
EDB: http://www.enterprisedb.com