Re: Function to move the position of a replication slot

On 2017-09-01 23:37:07 -0400, Tom Lane wrote:
> Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> writes:
> > On 8/31/17 08:19, Magnus Hagander wrote:
> >> I think that, in the end, covered all the comments?
>
> > I didn't see any explanation of what this would actually be useful for.
> > I suppose you could skip over some changes you don't want replicated,
> > but how do you find to what position to skip?
>
> Um ... I can see how you might expect to skip some events in a logical
> replication stream and have a chance of things not being utterly broken.
> But how can that work for physical replication? Missed updates are
> normally spelled "unrecoverable data corruption" at that level.

Consider e.g. a standby that follows master, but isn't a target for a
failover. It can make a fair bit of sense to script things so that
there's also a slot on the standby that's marked to be the primary in
disaster cases. For that you might want to forward the slot on a regular
basis.

I don't quite see how you'd get corruption from a physical slot being
forwarded? I mean you surely can get into the situation that there's
missing WAL from wherever a standby is receiving its WAL, but that'll
"just" break replication.

- Andres