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From: Paul Weiss <[email protected]>
To: David G. Johnston <[email protected]>
To: [email protected] <[email protected]>
Subject: Re: the concept of a database cluster
Date: Sat, 4 Jan 2020 09:58:57 +0000
Message-ID: <MWHPR15MB18397BC83DBD850FB8A2327CDC220@MWHPR15MB1839.namprd15.prod.outlook.com> (raw)
In-Reply-To: <CAKFQuwYgLTMZHyqEDO2ge=gx1deY70gSLvLVcmZWNToiZ+v3tQ@mail.gmail.com>
References: <[email protected]>
	<CAKFQuwYgLTMZHyqEDO2ge=gx1deY70gSLvLVcmZWNToiZ+v3tQ@mail.gmail.com>

Oh, I didn't mean to imply that I am confused. It is clear that there are two concepts here, sharing a term. I was trying to communicate that the manual does not always make it immediately clear from context which concept is meant in a particular sentence.

A garage is a good analogy. A garage is a container for cars rather than a collection of cars. You wouldn't say "I sold my garage" to mean "I sold my car collection". Containers and collections are different things.

Here's a simple example In our context: "remove the cluster" could mean "delete the folder containing the databases", or "drop the databases". Those actions are not identical. I would think we would want to be clear to our users which we mean.

Paul

________________________________
From: David G. Johnston <[email protected]>
Sent: Friday, January 3, 2020 12:21 AM
To: [email protected] <[email protected]>; [email protected] <[email protected]>
Subject: Re: the concept of a database cluster

On Thursday, January 2, 2020, PG Doc comments form <[email protected]<mailto:[email protected]>> wrote:
The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/12/creating-cluster.html
Description:

In 18.2, a database cluster is said to be "a database storage area on disk",
and then shortly afterward is is defined as "a collection of databases that
is managed by a single instance of a running database server". Those seem
very different things. Sometimes in the manual I can't tell which usage is
intended.

A garage is a “car storage area for a house”. A garage can (typically) store multiple cars just as a database cluster can store multiple databases.  The files are only useful if there is a running instance and all databases stored in the cluster are managed by a single shared instance.  You will need to better explain your confusion because the documentation is describing a complex system accurately but in parts that are related - two sides of the same coin, if you will.

David J.

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