On Sat, Oct 17, 2015 at 4:45 AM, Robert Haas <robertmh...@gmail.com> wrote:

> On Fri, Oct 16, 2015 at 2:52 PM, Peter Eisentraut <pete...@gmx.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 The release notes say that checkpoint_segments has been replaced by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,
(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...

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