Re: Prevent concurrent DROP SCHEMA when certain objects are being initially created in the namespace

>
> Something which would be good to have for all those queries is a set of
> isolation tests. No need for multiple specs, you could just use one
> spec with one session defining all the object types you would like to
> work on. How did you find this object list? Did you test all the
> objects available manually?
>
Attached the isolation spec file. I originally was only going to fix the
simple CREATE TYPE scenario but decided to look up other objects that can
reside in namespaces and ended up finding a handful of others. I tested
each one manually before and after adding the AccessShareLock acquire on
the schema.

I think that line of thought leads to an enormous increase in locking
> overhead, for which we'd get little if any gain in usability. So my
> inclination is to make an engineering judgment that we won't fix this.
>
As I was creating this patch, I had similar feelings on the locking
overhead and was curious how others would feel about it as well.

Regards,
Jimmy

On Tue, Sep 4, 2018 at 10:05 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On September 4, 2018 9:11:25 PM PDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> I think that line of thought leads to an enormous increase in locking
> >> overhead, for which we'd get little if any gain in usability. So my
> >> inclination is to make an engineering judgment that we won't fix this.
>
> > Haven't we already significantly started down this road, to avoid a lot
> of the "tuple concurrently updated" type errors?
>
> Not that I'm aware of. We do not take locks on schemas, nor functions,
> nor any other of the object types I mentioned.
>
> > Would expanding this a git further really be that noticeable?
>
> Frankly, I think it would be not so much "noticeable" as "disastrous".
>
> Making the overhead tolerable would require very large compromises
> in coverage, perhaps like "we'll only lock during DDL not DML".
> At which point I'd question why bother. We've seen no field reports
> (that I can recall offhand, anyway) that trace to not locking these
> objects.
>
> regards, tom lane
>