Date: Wed, 10 Oct 2018 15:50:02 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Michael Paquier <michael@paquier.xyz>,
	Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: file cloning in pg_upgrade and CREATE DATABASE
Message-ID: <20181010195002.GA7806@momjian.us>
References: <20181003014409.GC2609@paquier.xyz>
 <20181003020706.hykmk4vmy6brovoj@alvherre.pgsql>
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On Tue, Oct  2, 2018 at 11:07:06PM -0300, Alvaro Herrera wrote:
> 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.

Uh, if you use --link, and the two data directories are on different
file systems, it fails.  No one has ever asked for link-or-copy, so why
are we considering clone-or-copy?  Are we going to need
link-or-clone-or-copy too?  I do realize that clone and copy have
non-destructive behavior on the old cluster once started, so it does
make some sense to merge them, unlike link.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +