Date: Tue, 2 Oct 2018 23:07:06 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>,
	Bruce Momjian <bruce@momjian.us>
Subject: Re: file cloning in pg_upgrade and CREATE DATABASE
Message-ID: <20181003020706.hykmk4vmy6brovoj@alvherre.pgsql>
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On 2018-Oct-03, Michael Paquier wrote:

> On Tue, Oct 02, 2018 at 10:35:02PM -0300, Alvaro Herrera wrote:
> > I'm not clear what interface are you proposing.  Maybe they would just
> > use the clone-or-fail mode, and note whether it fails?  If that's not
> > it, please explain.
> 
> Okay.  What I am proposing is to not have any kind of automatic mode to
> keep the code simple, with a new option called --transfer-mode, able to
> do three things:
> - "link", which is the equivalent of the existing --link.
> - "copy", the default and the current behavior, which copies files.
> - "clone", the new mode proposed in this thread.

I see.  Peter is proposing to have a fourth mode, essentially
--transfer-mode=clone-or-copy.

Thinking about a generic tool that wraps pg_upgrade (say, Debian's
wrapper for it) this makes sense: just use the fastest non-destructive
mode available.  Which ones are available depends on what the underlying
filesystem is, so it's not up to the tool's writer to decide which to
use ahead of time.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services