Re: Fix slot synchronization with two_phase decoding enabled

On Wed, Jun 11, 2025 at 9:50 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Wed, Jun 11, 2025 at 11:31 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> >
> > BTW have we addressed the point Amit mentioned before[1]?
> >
> > > The one more combination to consider is when someone takes a dump of
> > > an older version and loads it into a newer version. For example, where
> > > users dump from 17.5 and then restore in a newer version, say 17.6
> > > (which has our fix), the restore will fail due to newer restrictions
> > > added by this patch. Do we need to do anything about it?
> >
> > I think it could be a significant side-effect and we need to do
> > something about that.
> >
>
> After giving it more thought, we have an opinion that this
> side-effect/issue is unlikely to occur if users follow our
> documentation properly.
>
> The recommended approach for upgrading between minor versions is to
> shut down the server and replace the binaries. See 'To update between
> compatible versions' in [1].
>
> Also it is recommended in docs that we use pg_dump from the newer
> version of PostgreSQL. See 'It is recommended that you use the
> pg_dump' in [2]. This particular recommendation is in the Upgrade doc.
> If needed, we can make a similar recommendation in any of our failover
> specific docs as well, mentioning this particular case.
>
> In brief, our overall understanding is that a) pg_dump is mainly used
> for major versions upgrade b) pg_dump of higher version is used.
> Please let us know if your understanding is different here.

I agree that the main use case of pg_dump is major version upgrading
but it's not limited to that use case. There might be some users who
have taken backups using pg_dump for truly backup purposes. I'm not
sure we've had such compatibility breakage in a minor version release.

> Beyond these steps, we could not find any better solution for the
> pointed case. But we are open to exploring and implementing any
> alternative solutions you may have. Feedback is most welcome here.

I'll share alternative ideas if I come up.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com