Re: Standalone synchronous master

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Stephen Frost <sfrost(at)snowman(dot)net>, Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Simon Riggs <simon(at)2ndQuadrant(dot)com>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Standalone synchronous master
Date: 2014-01-08 23:15:21
Message-ID: 52CDDC09.50301@agliodbs.com
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Stephen,

> I'm aware, my point was simply that we should state, up-front in
> 25.2.7.3 *and* where we document synchronous_standby_names, that it
> requires at least three servers to be involved to be a workable
> solution.

It's a workable solution with 2 servers. That's a "low-availability,
high-integrity" solution; the user has chosen to double their risk of
not accepting writes against never losing a write. That's a perfectly
valid configuration, and I believe that NTT runs several applications
this way.

In fact, that can already be looked at as a kind of "auto-degrade" mode:
if there aren't two nodes, then the database goes read-only.

Might I also point out that transactions are synchronous or not
individually? The sensible configuration is for only the important
writes being synchronous -- in which case auto-degrade makes even less
sense.

I really think that demand for auto-degrade is coming from users who
don't know what sync rep is for in the first place. The fact that other
vendors are offering auto-degrade as a feature instead of the ginormous
foot-gun it is adds to the confusion, but we can't help that.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com

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