Date: Thu, 18 Jun 2020 12:35:03 +0200
From: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Amit Kapila <amit.kapila16@gmail.com>,
 amul sul <sulamul@gmail.com>, PostgreSQL-development
 <pgsql-hackers@postgresql.org>
Subject: Re: [Patch] ALTER SYSTEM READ ONLY
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On Wed, 17 Jun 2020 12:07:22 -0400
Robert Haas <robertmhaas@gmail.com> wrote:
[...]

> > Commands that involve a whole
> > bunch of subtle interlocking --- and, therefore, aren't going to work if
> > anything has gone wrong already anywhere in the server --- seem like a
> > particularly poor thing to be hanging your HA strategy on.  
> 
> It's important not to conflate controlled switchover with failover.
> When there's a failover, you have to accept some risk of data loss or
> service interruption; but a controlled switchover does not need to
> carry the same risks and there are plenty of systems out there where
> it doesn't.

Yes. Maybe we should make sure the wording we are using is the same for
everyone. I already hear/read "failover", "controlled failover", "switchover" or
"controlled switchover", this is confusing. My definition of switchover is:

  swapping primary and secondary status between two replicating instances. With
  no data loss. This is a controlled procedure where all steps must succeed to
  complete.
  If a step fails, the procedure fail back to the original primary with no data
  loss.

However, Wikipedia has a broader definition, including situations where the
switchover is executed upon a failure: https://en.wikipedia.org/wiki/Switchover

Regards,