Re: Replication/backup defaults

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:
> > Cycling back to this topic again, but this time at the beginning of a CF.
> >
> > Here's an actual patch to change:
> >
> >
> > max_wal_senders=10
> > max_replication_slots=20
>
> +1
>
> If that doesn't fly, it seems easy enough to introduce a
> "min_reserve_limit" GUC that defaults to 10 that gives a lower bound
> on the amount of memory we reserve for many of those shmem allocs;
> that can be set to 0 for people that want the old behaviour. Then we
> can allow changes up to the memory limit without a restart.
>
> > wal_level=replica
>
> This is more problematic because it changes behaviours.
>

You can't actually change the other two without changing wal_level.

> A more useful approach would be to bring all the things needed to
> enable replication into one ALTER SYSTEM command, so people have just
> one thing they need to execute and it will work out the details and
> locations for you.
> That way we can maintain the defaults yet make it easier to enable in
> a useful way.
>

Sure, that would be great - the core being the ability to change these
things without a restart. But I would argue for not letting perfection get
in the way of progress, and do this anyway. I doubt there is any way the
bigger change is going to get done for 10 at this point, so we should give
people the ability to do backups off a default installation already.

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