From: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
Subject: Re: amazon aroura config - seriously overcommited defaults? (May be
 Off Topic)
To: Andres Freund <andres@anarazel.de>, Rob Sargent <robjsargent@gmail.com>
Cc: "pgsql-generallists.postgresql.org" <pgsql-general@lists.postgresql.org>,
 "pgsql-performance@lists.postgresql.org"
 <pgsql-performance@lists.postgresql.org>
References: <a053cc2d-bf74-cd33-09e1-024b7e87b494@yahoo.com>
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 <20181208231242.t66zpocct36m4o46@alap3.anarazel.de>
 <7AF20599-CCD4-43D9-962D-3EB7B3E25122@gmail.com>
 <20181208233818.qu5k5bb4mjklzcqw@alap3.anarazel.de>
Message-ID: <fa3376e8-fe4b-de59-47ce-2fc79d40eb53@2ndQuadrant.com>
Date: Sun, 9 Dec 2018 07:51:33 -0500
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On 12/8/18 6:38 PM, Andres Freund wrote:
> On 2018-12-08 15:23:19 -0800, Rob Sargent wrote:
>>
>>> On Dec 8, 2018, at 3:12 PM, Andres Freund <andres@anarazel.de> wrote:
>>>
>>> On 2018-12-08 12:06:23 -0800, Jeremy Schneider wrote:
>>>> On RDS PostgreSQL, the default is 25% of your server memory. This seems
>>>> to be pretty widely accepted as a good starting point on PostgreSQL.
>>> FWIW, I think it's widely cited, but also bad advice.  25% for a OLTP
>>> workload on a 1TB machine with a database size above 25% is a terrible
>>> idea.
>>>
>> Sorry, could you please expand “database size above 25%”?  25% of what?
> Memory available to postgres (i.e. 100% of the server's memory on a
> server dedicated to postgres, less if it's shared duty).
>


I think the best advice these days is that you need to triangulate to 
find the best setting for shared_buffers. It's very workload dependent, 
and there isn't even a semi-reliable rule of thumb.


cheers


andrew


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