Re: pg_dump versus hash partitioning

On Wed, Feb 1, 2023 at 2:12 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> 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.

Tom said:

"I spent a bit more time thinking about that, and while I agree that
it's an oddity, I don't see that it matters in the case of hash
partitioning. You would notice an issue if you tried to do a
selective restore of just one partition --- but under what
circumstance would that be a useful thing to do?"

While the word ambiguity may not have actually been used, Tom very
clearly admitted some ambiguity. But even if he didn't, so what? It's
perfectly obvious that that's the major underlying issue, and that
this is a high level problem rather than a low level problem.

> 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.

And I think that you're making a mountain out of a molehill.

> 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?

That was precisely the question that Tom posed to you, in the same
email as the one that you found objectionable.

> 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.

I don't know why you seem to think that it was such an absolutist
position as that.

You mentioned "minor releases" here. Who said anything about that?

--
Peter Geoghegan