Re: replication_slots usability issue

On 2018-10-30 11:51:09 +0900, Michael Paquier wrote:
> On Mon, Oct 29, 2018 at 12:13:04PM -0700, Andres Freund wrote:
> > I don't think this quite is the problem. ISTM the issue is rather that
> > StartupReplicationSlots() *needs* to check whether wal_level > minimal,
> > and doesn't. So you can create a slot, shutdown, change wal_level,
> > startup. A slot exists but won't work correctly.
>
> It seems to me that what we are looking for is just to complain at
> startup if we find any slot data and if trying to start up with
> wal_level = minimal.

Right, we really should just call CheckSlotRequirements() before doing
so. I'll make it so, once I'm actually awake and had some coffee.

> Er... At the same time, shouldn't RestoreSlotFromDisk() *not* use PANIC
> if more slots are found in pg_replslot than max_replication_slots can
> handle. A FATAL is fine at startup, PANIC blows up a core file, which
> is clearly overdoing it if the goal is to give a recommendation at the
> end.

I can't get particularly excited about this. I guess we can change it,
but I'd only do so in master.

Greetings,

Andres Freund