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Date: Sun, 17 May 2020 11:08:02 +0200
From: Erik Rijkers <er@xs4all.nl>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: =?UTF-8?Q?J=C3=BCrgen_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
In-Reply-To: <20200517065126.GA20730@alvherre.pgsql>
References: <20200517065126.GA20730@alvherre.pgsql>
Message-ID: <fcc01959cf90a5755819c50ae8005efa@xs4all.nl>
User-Agent: XS4ALL Webmail
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On 2020-05-17 08:51, Alvaro Herrera wrote:
> On 2020-May-17, Jürgen Purtz wrote:
> 
>> On 15.05.20 02:00, Alvaro Herrera wrote:
>> > Thanks everybody.  I have compiled together all the suggestions and the
>> >
>> > * I changed "instance", and made "cluster" be mostly a synonym of that.
>> In my understanding, "instance" and "cluster" should be different 
>> things,
> 
> 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 always 
understood this to be the same for the PostgreSQL 'instance'.  Once 
stopped, it is no longer an instance, but it is, of course, still a 
cluster.

I know, we don't have to do the same as Oracle, but clearly it's going 
to be an ongoing source of misunderstanding if we define such a 
high-level term differently.

Erik Rijkers