Clarification to pg_upgrade docs on reverting to old cluster

Daniel Gustafsson <[email protected]>
Newsgroups gmane.comp.db.postgresql.devel.documentation
Message-ID <qtqiv7hI87s_Xvz5ZXHCaH-1-_AZGpIDJowzlRjF3-AbCr3RhSNydM_JCuJ8DE4WZozrtxhIWmyYTbv0syKyfGB6cYMQitp9yN-NZMm-oAo=@yesql.se>
Reading the pg_upgrade reference page, I get the feeling that one of the
bullets under "Reverting to old cluster" is a bit thin on detail to be helpful
to newcomers:

    "If you ran pg_upgrade with --link, the data files are shared between the
    old and new cluster.  If you started the new cluster, the new server has
    written to those shared files and it is unsafe to use the old cluster."

This is perfectly correct, but it fails to provide information on what to do
next in case reverting is in fact what the user wants.  The attached patch adds
a short sentence saying the old cluster should be restored from backups at this
point.

cheers ./daniel
pg_upgrade_revert_cluster.patch (application/octet-stream, 1.1 KB)
From 1152e387399355e4df7ccb582adda51ccd594d69 Mon Sep 17 00:00:00 2001
From: Daniel Gustafsson <[email protected]>
Date: Thu, 4 Apr 2019 21:21:48 +0200
Subject: [PATCH] docs: extend the pg_upgrade docs for cluster revert

Add a small clarification to the pg_upgrade documentation regarding
reverting to the old cluster.
---
 doc/src/sgml/ref/pgupgrade.sgml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/ref/pgupgrade.sgml b/doc/src/sgml/ref/pgupgrade.sgml
index c896882dd1..655802f8d6 100644
--- a/doc/src/sgml/ref/pgupgrade.sgml
+++ b/doc/src/sgml/ref/pgupgrade.sgml
@@ -690,7 +690,8 @@ psql --username=postgres --file=script.sql postgres
         with <option>--link</option>, the data files are shared between the
         old and new cluster. If you started the new cluster, the new
         server has written to those shared files and it is unsafe to
-        use the old cluster.
+        use the old cluster.  The old cluster will need to be restored from
+        backups at this point.
        </para>
       </listitem>
 
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2.14.1.145.gb3622a4ee
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