Re: [HACKERS] Custom compression methods

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Mar 24, 2021 at 11:42 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> On reflection, though, I wonder if we've made pg_dump do the right
>> thing anyway. There is a strong case to be made for the idea that
>> when dumping from a pre-14 server, it should emit
>> SET default_toast_compression = 'pglz';
>> rather than omitting any mention of the variable, which is what
>> I made it do in aa25d1089.

> But also ... aren't we just doing this to work around a test case that
> isn't especially good in the first place? Counting the number of lines
> in the diff between A and B is an extremely crude proxy for "they're
> similar enough that we probably haven't broken anything."

I wouldn't be proposing this if the xversion failures were the only
reason; making them go away is just a nice side-effect. The core
point is that the charter of pg_dump is to reproduce the source
database's state, and as things stand we're failing to ensure we
do that.

(But yeah, we really need a better way of making this check in
the xversion tests. I don't like the arbitrary "n lines of diff
is probably OK" business one bit.)

regards, tom lane