Re: allowing wal_level change at run time

On Tue, Aug 18, 2015 at 1:59 PM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:

> In [1], it was discussed to make wal_level changeable at run time
> (PGC_SIGHUP), as part of an effort to make replication easier to set up
> and/or provide better defaults. I was wondering what it would take to
> do that.
>
> I looks like increasing the setting is doable, as long as we WAL-log the
> change using existing facilities. I don't understand the hot_standby ->
> logical transition, so maybe something else is necessary there.
>
> How would we handle decreases at run time? We can prevent >=archive ->
> minimal if archiving is running or there are physical replication slots,
> and we can prevent logical -> something less if there are logical
> replication slots, but AFAICT, we don't have a way to check whether
> anyone currently needs level hot_standby. (Thread [1] originally
> proposed to get rid of the archive/hot_standby distinction, which would
> help here.) Or we could just let users make their own mess if they want
> to.
>

I still think we should get rid of the difference between
archive/hot_standby. It creates more trouble than I've ever seen it save. I
think we can safely label that as something we added because we didn't know
if it was going to be needed (because back in 9.0 nobody knew what the
impact *really* would be), but now we know it's not necessary so we can
just get rid of it.

Especially as it makes something like this easier. Removing complexity of
such important parts of the code is a feature in itself!

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/