Date: Sun, 17 May 2020 11:28:51 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Erik Rijkers <er@xs4all.nl>
Cc: =?iso-8859-1?Q?J=FCrgen?= Purtz <juergen@purtz.de>,
	Laurenz Albe <laurenz.albe@cybertec.at>,
	Fabien COELHO <coelho@cri.ensmp.fr>,
	Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	Corey Huinker <corey.huinker@gmail.com>,
	Justin Pryzby <pryzby@telsasoft.com>,
	Roger Harkavy <rogerharkavy@gmail.com>,
	pgsql-hackers@postgresql.org, Michael Paquier <michael@paquier.xyz>
Subject: Re: Add A Glossary
Message-ID: <20200517152851.GA31376@alvherre.pgsql>
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On 2020-May-17, Erik Rijkers wrote:

> On 2020-05-17 08:51, Alvaro Herrera wrote:

> > I don't think that's the general understanding of those terms.  For all
> > I know, they *are* synonyms, and there's no specific term for "the
> > fluctuating objects" as you call them.  The instance is either running
> > (in which case there are processes and RAM) or it isn't.
> 
> For what it's worth, I've also always understood 'instance' as 'a running
> database'.  I admit it might be a left-over from my oracle years:
> 
> https://docs.oracle.com/cd/E11882_01/server.112/e40540/startup.htm#CNCPT601
> 
> There, 'instance' clearly refers to a running database.  When that database
> is stopped, it ceases to be an instance.

I've never understood it that way, but I'm open to having my opinion on
it changed.  So let's discuss it and maybe gather opinions from others.

I think the terms under discussion are just

* cluster
* instance
* server

We don't have "host" (I just made it a synonym for server), but perhaps
we can add that too, if it's useful.  It would be good to be consistent
with historical Postgres usage, such as the initdb usage of "cluster"
etc.

Perhaps we should not only define what our use of each term is, but also
explain how each term is used outside PostgreSQL and highlight the
differences.  (This would be particularly useful for "cluster" ISTM.)

It seems difficult to get this sorted out before beta1, but there's
still time before the glossary is released.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services