Re: file cloning in pg_upgrade and CREATE DATABASE

On Wed, Jun 06, 2018 at 11:58:14AM -0400, Peter Eisentraut wrote:
> <para>
> The setting <literal>always</literal> requires the use of relinks. If
> they are not supported, the <application>pg_upgrade</application> run
> will abort. Use this in production to limit the upgrade run time.
> The setting <literal>auto</literal> uses reflinks when available,
> otherwise it falls back to a normal copy. This is the default. The
> setting <literal>never</literal> prevents use of reflinks and always
> uses a normal copy. This can be useful to ensure that the upgraded
> cluster has its disk space fully allocated and not shared with the old
> cluster.
> </para>

Hm... I am wondering if we actually want the "auto" mode where we make
the option smarter automatically. I am afraid of users trying to use it
and being surprised that there is no gain while they expected some. I
would rather switch that to an on/off switch, which defaults to "off",
or simply what is available now. huge_pages=try was a bad idea as the
result is not deterministic, so I would not have more of that...

Putting CloneFile and check_reflink in a location that other frontend
binaries could use would be nice, like pg_rewind.
--
Michael