Re: error handling in RegisterBackgroundWorker

"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Tue, Apr 11, 2017 at 11:10 AM, Peter Eisentraut <
> peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
>> On 4/11/17 11:47, David G. Johnston wrote:
>>> ​A potential middle-ground is to start, but then only allow superuser
>>> connections.

>> Then you might as well start and allow all connections. I don't see
>> what this buys.

> If "leave it offline until it gets fixed" is on the table then there is
> some underlying reason that we'd not want application (or replication)
> users connecting to the database while it is in a degraded state. Even if
> one accepts that premise that doesn't mean that an administrator shouldn't
> be allowed to login and do ad-hoc stuff; the goal of the prevention is to
> disallow programmed external actors that assume/require that these
> background worker processes are active from connecting while they are not.
> This middle-ground accommodates that goal in a precise manner.

Only if you assume that those external scripts aren't connecting as
superuser. Unfortunately, that assumption is probably widely violated,
especially in the sort of less-well-run installations that are most
at risk for the kind of problem we're speculating about here.

> I don't have an opinion as to which extreme is better so in the absence I'm
> in favor of "put control in the hands of the administrator" - this just
> provides a slightly more usable environment for the administrator to
> operate within.

Yeah, "usable environment" is key here. A point I meant to bring up
earlier today is that we do already have a solution for degraded
operation, ie, run a standalone backend. But that's so awful, from
any standpoint including UI friendliness (no psql, let alone pgadmin or
other GUI tools), performance (no bgwriter, walwriter, stats collector,
or autovacuum), or reliability (no automatic checkpoints, never mind
replication), that nobody in their right mind would choose to use it
until their back was very hard against the wall. So what we're
really discussing here is intermediate operating modes where you have
at least some of those facilities. I doubt there are black-and-white
answers, but I still believe in the likely usefulness of a mode where
we start as much of that stuff as we can.

regards, tom lane