Date: Sun, 17 May 2020 02:51:26 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: =?iso-8859-1?Q?J=FCrgen?= Purtz <juergen@purtz.de>
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>
Subject: Re: Add A Glossary
Message-ID: <20200517065126.GA20730@alvherre.pgsql>
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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
> > result is in the attached patch.  Some of it is of my own devising.
> > 
> > * I changed "instance", and made "cluster" be mostly a synonym of that.
> In my understanding, "instance" and "cluster" should be different things,
> not only synonyms. "instance" can be the term for permanently fluctuating
> objects (processes and RAM) and "cluster" can denote the more static objects
> (directories and files). What do you think? If you agree, I would create a
> patch.

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.


> > * I removed "global SQL object" and made "SQL object" explain it.
> +1., but see the (huge) different spellings in patch.

This seems a misunderstanding of what "local" means.  Any object that
exists in a database is local, regardless of whether it exists in a
schema or not.  "Extensions" is one type of object that does not belong
in a schema.  "Foreign data wrapper" is another type of object that does
not belong in a schema.  Same with data type casts.  They are *not*
global objects.

> bloat: changed 'current row' to 'relevant row' because not only the youngest
> one is relevant (non-bloat).

Hm.  TBH I'm not sure of this term at all.  I think we sometimes use the
term "bloat" to talk about the dead rows only, ignoring the free space.

> data type casts: Are you sure that they are global? In pg_cast 'relisshared'
> is 'false'.

I'm not saying they're global.  I'm saying they're outside schemas.
Maybe this definition needs more rewording, if this bit is unclear.

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