Re: Skipping logical replication transactions on subscriber side

On Wed, Jun 22, 2022 at 10:39 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> That's a fundamental misreading of the situation. typalign is essential
> on alignment-picky architectures, else you will get a SIGBUS fault
> when trying to fetch a multibyte value (whether it's just going to get
> stored into a Datum array is not very relevant here).

I mean, that problem is easily worked around. Maybe you think memcpy
would be a lot slower than a direct assignment, but "essential" is a
strong word.

> I concur that Noah's description of #2 is not an accurate statement
> of the rules we'd have to impose to be sure that the C structs line up
> with the actual tuple layouts. I don't think we want rules exactly,
> what we need is mechanical verification that the field orderings in
> use are safe. The last time I looked at this thread, what was being
> discussed was (a) re-ordering pg_subscription's columns and (b)
> adding some kind of regression test to verify that all catalogs meet
> the expectation of 'd'-aligned fields not needing alignment padding
> that an AIX compiler might choose not to insert. That still seems
> like the most plausible answer to me. I don't especially want to
> invent an additional typalign code that we could only test on legacy
> platforms.

I agree with that, but I don't think that having the developers
enforce alignment rules by reordering catalog columns for the sake of
legacy platforms is appealing either.

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