Subject: Re: Add A Glossary
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Erik Rijkers <er@xs4all.nl>, 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>,
 Pg Docs <pgsql-docs@lists.postgresql.org>
References: <20200517152851.GA31376@alvherre.pgsql>
From: =?UTF-8?Q?J=c3=bcrgen_Purtz?= <juergen@purtz.de>
Message-ID: <c1e06008-2132-30f4-9b38-877e8683d418@purtz.de>
Date: Tue, 9 Jun 2020 13:25:04 +0200
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On 17.05.20 17:28, Alvaro Herrera wrote:
> I think the terms under discussion are just
>
> * cluster
> * instance
> * server


Despite the short period of its existence the glossary achieved some 
importance, see: 
https://www.postgresql.org/message-id/b8e12875ebec9e6d3107df5fa1129e1e%40postgrespro.ru 
. We have to be careful with publications. It's not acceptable that we 
change definitions from release to release. Therefore IMO we should mark 
or even ignore such terms for which we cannot reach consensus.

Can you agree to the following definitions? If no, we can alternatively 
formulate for each of them: "Under discussion - currently not defined". 
My proposals are inspired by chapter 2.2 Concepts: "Tables are grouped 
into databases, and a collection of databases managed by a single 
PostgreSQL server instance constitutes a database cluster."


- "Database" (No change to existing definition): "A named collection of 
SQL objects."


- "Database Cluster", "Cluster" (New definition and rearrangements of 
some sentences): "A collection of related databases, and their common 
static and dynamic meta-data.

This term is sometimes used to refer to an instance.

(Don't confuse the term CLUSTER with the SQL command CLUSTER.)"


- "Data Directory" (Replaced 'instance' by 'cluster'): "The base 
directory on the filesystem of a server that contains all data files and 
subdirectories associated with a cluster (with the exception of 
tablespaces). The environment variable PGDATA is commonly used to refer 
to the data directory.

A cluster's storage space comprises the data directory plus any 
additional tablespaces.

For more information, see Section 68.1."


- "Database Server", "Instance" (Major changes): "A group of backend and 
auxiliary processes that communicate using a common shared memory area. 
One postmaster process manages the instance; one instance manages 
exactly one cluster with all its databases. Many instances can run on 
the same server as long as their TCP ports do not conflict.

The instance handles all key features of a DBMS: read and write access 
to files and shared memory, assurance of the ACID properties, 
connections to client processes, privilege verification, crash recovery, 
replication, etc."


- "Server" (No change to existing definition): "A computer on which 
PostgreSQL instances run. The term server denotes real hardware, a 
container, or a virtual machine.

This term is sometimes used to refer to an instance or to a host."


- "Host" (No change to existing definition): "A computer that 
communicates with other computers over a network. This is sometimes used 
as a synonym for server. It is also used to refer to a computer where 
client processes run."


--

Jürgen Purtz