Re: Replication/backup defaults

On Mon, Jan 02, 2017 at 10:21:41AM +0100, Magnus Hagander wrote:
> On Mon, Jan 2, 2017 at 10:17 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On 31 December 2016 at 15:00, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> > > max_wal_senders=10
> > > max_replication_slots=20

[...]

> > > wal_level=replica
> >
> > This is more problematic because it changes behaviours.
>
> You can't actually change the other two without changing wal_level.

That actually goes both ways: I recently saw a server not start cause we
were experimenting with temporarily setting wal_level to minimal for
initial bulk loading, but did not reduce max_wal_senders back to zero.
So it failed at startup with 'FATAL: WAL streaming (max_wal_senders >
0) requires wal_level "replica" or "logical"'.

I don't want to hijack this thread, but I wonder whether the name
"*max*_wal_senders" really conveys that dependence on wal_level (there's
no comment to that end in the postgresql.conf sample) and/or whether
maybe the admin should just be notified that WAL streaming is turned off
cause wal_level < 'replica'?

Michael

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