Horton

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

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Stephen Frost <sfrost@snowman.net>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Martijn van Oosterhout <kleptog@svana.org>, Alvaro Herrera <alvherre@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Dimitri Fontaine <dimitri@2ndquadrant.fr>, Andres Freund <andres@2ndquadrant.com>, Josh Berkus <josh@agliodbs.com>, Tom Lane <tgl@sss.pgh.pa.us>, Fujii Masao <masao.fujii@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2013-08-22T16:04:08Z
Lists: pgsql-hackers 
On Thu, Aug 22, 2013 at 08:36:37AM -0400, Stephen Frost wrote:
> * Amit Kapila (amit.kapila16@gmail.com) wrote:
> >    This can resolve the problem of whether to read auto file rather
> > cleanly, so the idea is:
> > 
> > Enable/Disable reading of auto file
> > -----------------------------------------------------
> > a. Have a new include in postresql.conf
> >     #include_auto_conf_file    postgresql.auto.conf
> >     as it is a special include, we can read this file relative to data
> > directory.

The big advantage of using 'include_auto_conf_file' and not simply
'include' is that we can issue an error from ALTER SYSTEM SET if that is
not set.

> > Enable/Disable Alter System command
> > -----------------------------------------------------------
> > This can be achieved in 3 ways:
> > a. Check before executing Alter System if include directive is
> > disabled, then just issue a warning to user and proceed with command.
> > b. Check before executing Alter System if include directive is
> > disabled, then just issue an error and stop.
> 
> It doesn't make sense for it to be a 'warning' with this- the
> parameter specifies the file to use.  If you don't know what file to
> use, how you can possibly do anything but return an error?

Agreed.  No sense in allowing users to add things to the 'auto' file
when the auto file is inactive.

> Note that I *like* that about this approach.
> 
> There are a few other considerations with this-
> 
> - What should the default be?  (Still thinking 'off' myself)

Probably, but we might need to wait until we have a final API for a
decision on that.

> - What happens if the user specifies 'postgresql.conf'?  I'm thinking we
>   would disallow such insanity (as that's what it is, imv..) by having
>   an identifier in the file that this is the PG "auto conf" file.

I am thinking they can't include a value equal to 'config_file', which
is normally postgresql.conf.  I am not a big fan of looking for special
text in files.  This might be complex to check, though, because of path
changes --- we might just disallow the basement from matching the
basename of config_file.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +