On 8/3/19 7:56 AM, Andres Freund wrote:
Hi,
On 2019-08-02 18:47:07 -0400, Tom Lane wrote:
Stephen Frost <sfr...@snowman.net> writes:
I disagree that this should only be addressed in alter system, as I’ve said
before and as others have agreed with. Having one set of code that can be
used to update parameters in the auto.conf and then have that be used by
pg_basebackup, alter system, and external tools, is the right approach.
I don't find that to be necessary or even desirable. Many (most?) of the
situations where this would be important wouldn't have access to a running
backend, and maybe not to any PG code at all --- what if your tool isn't
written in C?
I think a commandline tool to perform the equivalent of ALTER SYSTEM on
a shutdown cluster would be a great tool. It's easy enough to add
something with broken syntax, and further down the road such a tool
could not only ensure the syntax is correct, but also validate
individual settings as much as possible (obviously there's some hairy
issues here).
What I came up with shoehorned a stripped-down version of the backend
config parser into fe_utils and provides a function to modify pg.auto.conf
in much the same way ALTER SYSTEM does, but with only the basic syntax
checking provided by the parser of course. And for completeness a
client utility which can be called by scripts etc.
I can clean it up and submit it later for reference (got distracted by other
things
recently) though I don't think it's a particularly good solution due to the
lack of actual checks for the provided GUCSs (and the implementation
is ugly anyway); something like what Andres suggests below would be far better.
Quite possibly the most realistic way to implement something like that
would be a postgres commandline switch, which'd start up far enough to
perform GUC checks and execute AlterSystem(), and then shut down
again. We already have -C, I think such an option could reasonably be
implemented alongside it.
Obviously this is widely out of scope for v12.
Regards
Ian Barwick
--
Ian Barwick https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
