From: Jerry Sievers <gsievers19@comcast.net>
To: bricklen <bricklen@gmail.com>
Cc: "Hammerman\, Joseph" <JosephHammerman@iheartmedia.com>,
  "pgsql-admin\@postgresql.org" <pgsql-admin@postgresql.org>
Subject: Re: Failover with a tertiary read-only secondary
References: <D503FB0C.6C95%JosephHammerman@iheartmedia.com>
	<CAGrpgQ8cbQJc3iFq2KQ2dA5O76-r3t_EB1MiApY2oNRt6UYnRg@mail.gmail.com>
	<D5041934.6CA6%JosephHammerman@iheartmedia.com>
	<CAGrpgQ8chc67K0M+XYRfAAjyHcRp5tEjHd-FYOh4o+E4zLBM9w@mail.gmail.com>
Date: Fri, 31 Mar 2017 17:45:58 -0500
In-Reply-To: 
 <CAGrpgQ8chc67K0M+XYRfAAjyHcRp5tEjHd-FYOh4o+E4zLBM9w@mail.gmail.com>
	(bricklen@gmail.com's message of "Fri, 31 Mar 2017 11:40:12 -0700")
Message-ID: <86y3vlqd3t.fsf@jerry.enova.com>
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bricklen <bricklen@gmail.com> writes:

> On Fri, Mar 31, 2017 at 11:35 AM, Hammerman, Joseph <JosephHammerman@iheartmedia.com> wrote:
>
>      1. Not a bad idea, but that only delays the necessity of a resync until the next failover…. Unless I’m missing something?
>
> I've used cascading replication extensively over the past few years and rarely had to resync a downstream replica. The several thousand Postgres clusters I'm
> administering now are almost exclusively set up with the primary replica streaming from the master and the master shipping WALs to the secondary replica in DR data
> centre, so I can't test any cascading replication promotions at the moment. My suggestion is to test your replication setup in a cascade and see what happens, I don't
> expect you'll need to resync. If you do, report back with how you've set up your replication settings.

Repointing tertiary standbys to a promoted peer should not be difficult
if same tertiary standby was at or trailing the log position when new
master promoted... and recovery.conf has recovery_target_timeline=latest.

Also, the new promoted master needs to have been already configured to
archive and wal_level set not minimal on promotion.

In other words, there shall be no break in the WAL stream in regards to
adequate wal level which depends on the tertiary standby's needs.

HTH

>

-- 
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres.consulting@comcast.net
p: 312.241.7800


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