Re: improving wraparound behavior

Greetings,

* Andres Freund (andres(at)anarazel(dot)de) wrote:
> I don't think we necessarily need a new WAL record for what I'm
> describing above (as XLOG_SMGR_TRUNCATE already carries information
> about which forks are truncated, we could just have it acquire the
> exclusive lock), and I don't think we'd need a ton of code for eliding
> the WAL logged lock either. Think the issue with backpatching would be
> that we can't remove the logged lock, without creating hazards for
> standbys running older versions of postgres.

While it's pretty rare, I don't believe this would be the only case of
"you need to upgrade your replicas before your primary" due to changes
in WAL. Of course, we need to make sure that we actually figure out
that the WAL being sent is something that the replica doesn't know how
to properly handle because it's from a newer primary; we can't simply do
the wrong thing in that case.

Thanks,

Stephen