Re: warn if GUC set to an invalid shared library

On Sat, Jan 8, 2022 at 2:07 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
> Unfortunately, the output for dlopen() is not portable, which (I think) means
> most of what I wrote can't be made to work.. Since it doesn't work to call
> dlopen() when using SET, I tried using just stat(). But that also fails on
> windows, since one of the regression tests has an invalid filename involving
> unbalanced quotes, which cause it to return EINVAL rather than ENOENT. So SET
> cannot warn portably, unless it includes no details at all (or we specially
> handle the windows case), or change the pre-existing regression test. But
> there's a 2nd instability, too, apparently having to do with timing. So I'm
> planning to drop the 0001 patch.

Hmm. I think 001 is a big part of the usability improvement here.
Could we not at least warn generically, without relaying the
underlying error? The notable thing in this situation is that the
specified library could not be loaded (and that it will almost
certainly cause problems on restart). The specific error would be nice
to have, but it's less important. What is the timing instability?

> > On Tue, Dec 28, 2021 at 9:45 AM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
> > For whatever reason, I get slightly different (and somewhat redundant)
> > output on failing to start:
> >
> > 2022-01-08 12:59:36.784 PST [324482] WARNING: could not load library: $libdir/plugins/totally bogus: cannot open shared object file: No such file or directory
> > 2022-01-08 12:59:36.787 PST [324482] FATAL: could not load library: totally bogus: cannot open shared object file: No such file or directory
> > 2022-01-08 12:59:36.787 PST [324482] LOG: database system is shut down
>
> I think the first WARNING is from the GUC mechanism "setting" the library.
> And then the FATAL is from trying to apply the GUC.
> It looks like you didn't apply the 0002 patch for that test so got no CONTEXT ?

I still had the terminal open where I tested this, and the scrollback
did show me applying the patch (and building after). I tried a make
clean and applying the patch again, and I do see the CONTEXT line now.
I'm not sure what the problem was but seems like PEBKAC--sorry about
that.

Thanks,
Maciek