From: =?UTF-8?Q?J=c3=bcrgen_Purtz?= <juergen@purtz.de>
Subject: Re: Add A Glossary
To: Laurenz Albe <laurenz.albe@cybertec.at>,
 Justin Pryzby <pryzby@telsasoft.com>,
 Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Erik Rijkers <er@xs4all.nl>, Corey Huinker <corey.huinker@gmail.com>,
 Roger Harkavy <rogerharkavy@gmail.com>, pgsql-hackers@postgresql.org,
 Fabien COELHO <coelho@cri.ensmp.fr>, Michael Paquier <michael@paquier.xyz>
References: <7b9b469e804777ac9df4d37716db935e@xs4all.nl>
 <20200403205143.GA7961@alvherre.pgsql> <20200403210120.GA12283@telsasoft.com>
 <686e65ba48801791816771e993ff5eebe571fac9.camel@cybertec.at>
Message-ID: <19521520-719c-5c47-d196-3385617d5c03@purtz.de>
Date: Sat, 4 Apr 2020 14:30:14 +0200
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> - Server: is that really our definition?
>    I thought that "server" is what the glossary defines as "instance", and
>    the thing called "server" in the glossary should really be called "host".
>
>    Maybe I am too Unix-centered.
>
>    Many people I know use "instance" synonymous to "cluster".

Currently our documentation uses 'server', 'database server', 'host', 
'instance', ...  in an indifferent way. Similar problem with 
database/cluster. Now we have the chance to come to a conclusion about 
preferred terms an their exact meaning. Definitions in the glossary 
shall be the guideline, the documentation itself can adopt these terms 
over time.

Here is my point of view. We have distinguishable things:

(1) (virtual) hardware

(2) an abstract structure of several object types, which models a 
management system for data

(3) a group of closely related processes. They implement the internal 
'business logic' or 'work flow' of (2).

(4) abstract data, which fits into (2)

(5) a physical representation of (4). Mainly and long lasting on disc, 
but - partly - mirrored in RAM.

(6) client processes, which connect to (3)


IMO for (1) the two terms 'server' and 'host' both have their 
justification, depending on the context. There are historical terms 
('server-side', 'foreign server', 'client/server architecture', 'host' 
or 'host name' for IP-specification, 'host variable') which cannot be 
changed. Therefor we shall accept both with identical definition and use 
them as synonyms. Independent from this, there are many paragraphs in 
the documentation, where they are used in a misleading sense ('server 
crash', '... started the server', 'database server'). They should be 
changed over time.

For me, (3) is an 'instance' and (5) is a 'cluster'. There is a 1:1 
relation between the two, because one 'instance' controls exactly one 
'cluster'. But the 'instance' consists of processes and memory whereas 
the 'cluster' of databases which resides (mainly) on disc.

Concerning (6) we are not interested in any hardware-question. We are 
only interested in the processes, which connect to backend processes. We 
should only define the term "Client process".

Kind regards, Jürgen