Re: ALTER SYSTEM SET command to change postgresql.conf parameters (RE: Proposal for Allow postgresql.conf values to be changed via SQL [review])

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Greg Smith <greg(at)2ndQuadrant(dot)com>, Amit kapila <amit(dot)kapila(at)huawei(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, 'Fujii Masao' <masao(dot)fujii(at)gmail(dot)com>, 'Robert Haas' <robertmhaas(at)gmail(dot)com>
Subject: Re: ALTER SYSTEM SET command to change postgresql.conf parameters (RE: Proposal for Allow postgresql.conf values to be changed via SQL [review])
Date: 2013-07-22 23:35:47
Message-ID: 51EDC1D3.2020409@agliodbs.com
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All,

Christophe just discovered something with include files which is going
to cause issues with ALTER SYSTEM SET.

So, take as a hypothetical that you use the default postgresql.conf
file, which sets shared_buffers = 32MB.

Instead of editing this file, you do ALTER SYSTEM SET shared_buffers =
'1GB', which updates config/postgresql.auto.conf.

Then you restart PostgreSQL.

Everything is hunky-dory, until a later occasion where you *reload*
postgresql. Then postgres startup hits the first "shared_buffers=32MB"
(in postgresql.conf), says "I can't change shared buffers on a reload",
and aborts before ever getting to postgresql.auto.conf.

This is a problem that exists now with includes in postgresql.conf, but
having ALTER SYSTEM SET will cause more users to hit it. Seems like
we'll need to fix it before releasing 9.4.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com

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