Re: Re: [COMMITTERS] pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

Kevin Grittner <kgrittn(at)gmail(dot)com> writes:
> On Tue, Apr 12, 2016 at 12:08 PM, Alvaro Herrera
> <alvherre(at)2ndquadrant(dot)com> wrote:
>> old_snapshot_threshold is PGC_POSTMASTER, so this is okay AFAICS, but
>> perhaps it'd be a good idea to add a oneline comment to guc.c indicating
>> to verify this code if there's an intention to lift that limitation --

> Perhaps, but this would be one of at least a dozen land mines that
> exist for trying to modify this setting to be read on reload.
> FWIW, I spent a fair amount of time trying to make it PGC_SIGHUP,
> since it would be very nice to allow that; but I kept running into
> one problem after another with it, some of which were very hard to
> see how to fix.

It'd be good if you document the problems you found somewhere, before
you forget them, just in case somebody does want to try to lift the
restriction. I agree that scattered code comments wouldn't be the way.
Just a quick email to -hackers to get the info into the archives
might be enough.

regards, tom lane