On Mon, Dec 21, 2020 at 09:42:47AM -0800, Andres Freund wrote:
> On 2020-12-20 15:54:31 -0800, Peter Geoghegan wrote:
> > On Sun, Dec 20, 2020 at 3:13 PM Andres Freund <andres@anarazel.de> wrote:
> > > Hm. Do I understand correctly that this problem is hit solely because
> > > the parallel mode code relies on there already have been a transaction
> > > snapshot set, thus avoiding the error? And that the code normally only
> > > works because GetTransactionSnapshot() will already have been called
> > > somewhere, before EnterParallelMode()?
> >
> > It seems unlikely that InitializeParallelDSM() was ever intended to be
> > run in a background worker.
>
> IDK, the environment in a bgworker shouldn't be that different from the
> normal query environment in a normal connection. And it's far from
> insane to want to be able to run a paralell query in a bgworker (and I
> *think* I have seen that work before). This case here seems more like
> an accidental dependency than anything to me, once that could perhaps
> even hint at problems in normal backends too.
Yeah. SPI_execute("TRUNCATE foo", false, 0) has no trouble doing a parallel
index build in a bgworker. Let's ignore intention and be pleased about that.
