From: Jerry Sievers <gsievers19@comcast.net>
To: Bob Jolliffe <bobjolliffe@gmail.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Interpreting shared_buffers setting
References: 
 <CACd=f9f1ODAgnEsUagdfyChEXsE4OD5V3LyXvuUozquZUgYo9A@mail.gmail.com>
Date: Tue, 29 Jan 2019 12:31:51 -0600
In-Reply-To: 
 <CACd=f9f1ODAgnEsUagdfyChEXsE4OD5V3LyXvuUozquZUgYo9A@mail.gmail.com>
	(Bob Jolliffe's message of "Tue, 29 Jan 2019 12:32:55 +0000")
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Bob Jolliffe <bobjolliffe@gmail.com> writes:

> Excuse me if this is a silly question.  I am trying to fiddle with
> shared_buffers setting on postgresql 10.6 on ubuntu 18.04 server.
>
> I have this at bottom of my config file:
> shared_buffers = 1GB
>
> Yet when I check the setting from pg_setting I see something quite different:
>
> postgres=# SELECT name, setting FROM pg_settings where name = 'shared_buffers';
>       name      | setting
> ----------------+---------
>  shared_buffers | 131072

Why not use the show command which is good about output in human
terms...

psql (11.1 (Ubuntu 11.1-1.pgdg16.04+1))
Type "help" for help.

meta_a:postgres# select name, setting from pg_settings where name = 'shared_buffers');
ERROR:  syntax error at or near ")"
LINE 1: ...me, setting from pg_settings where name = 'shared_buffers');
                                                                     ^
meta_a:postgres# 

>
> Is this a question of units?  It looks like 128M.  Note when I change
> the setting to 2GB in conf file I see 262144 from pg_setting.  I am
> now unsure what the actual shared_buffers allocation is.  I cant see
> anything in the docs which tells me how to interpret the integer.
>
> Any clarification welcome.
>
> Regards
> Bob
>
>

-- 
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres.consulting@comcast.net