Re: checkpoint_segments upgrade recommendation?

On Sat, Oct 17, 2015 at 4:45 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Fri, Oct 16, 2015 at 2:52 PM, Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:
> > The release notes say that checkpoint_segments has been replaced by
> > max_wal_size and min_wal_size, but there is no indication on how to
> > convert between the old and new settings. I think a lot of people will
> > have checkpoint_segments delicately tuned, so we should at least give
> > them a hint on how to carry that forward in spirit.
>
> Yeah, it would be nice to have some guidance about that. But do we
> know what the guidance should be?
>

I think that we should just suggest a reverse formula of the maximum soft
limit of checkpoint_segments for max_wal_size in the release notes of 9.5,
basically:
(3 * your_old_checkpoint_segments + 1) * 16MB = max_wal_size
I am not sure it is worth mentioning that one needs to be be sure to keep
some extra room to handle potential spikes because that's not a hard limit,
but people who have already played with pg_xlog on a different partition
are already aware of that after tuning checkpoint_segments.
min_wal_size is a new parameter though, I don't think it matters much to
hint users for the transfer to the new configuration...
Regards,
--
Michael