Re: Parallel INSERT (INTO ... SELECT ...)

On Fri, Mar 12, 2021 at 1:33 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> > > The problem is that target_rel_trigger_max_parallel_hazard and its
> > > caller think they can use a relcache TriggerDesc field across other
> > > cache accesses, which they can't because the relcache doesn't
> > > guarantee that that won't move.
> > >
> > > One approach would be to add logic to RelationClearRelation similar to
> > > what it does for tupdescs, rules, etc, to avoid moving them when their
> > > contents haven't changed. But given that we've not needed that for
> > > the past several decades, I'm disinclined to add the overhead. I
> > > think this code ought to be adjusted to not make its own copy of the
> > > trigdesc pointer, but instead fetch it out of the relcache struct each
> > > time it is accessed. There's no real reason why
> > > target_rel_trigger_max_parallel_hazard shouldn't be passed the
> > > (stable) Relation pointer instead of just the trigdesc pointer.
> > >
> >
> > I have attached a patch to fix the issue, based on your suggestion (tested with
> > CLOBBER_CACHE_ALWAYS defined).
> >
> > > BTW, having special logic for FK triggers in
> > > target_rel_trigger_max_parallel_hazard seems quite loony to me.
> > > Why isn't that handled by setting appropriate proparallel values for
> > > those trigger functions?
> > >
> >
> > ... and also attached a patch to update the code for this issue.
> >
> > (2nd patch relies on application of the 1st patch)
> >
> > Thanks again for pointing out these problems.
>
> I have tested the triggerdesc bugfix patch with CLOBBER_CACHE_ALWAYS flag.
> It passed the testset where is fail in buildfarm (foreign_key, foreign_data).
>

Thanks for the patch and review. It looks good to me as well and
passes the tests (foreign_key, foreign_data) with CLOBBER_CACHE_ALWAYS
flag.

I'll review the second patch of Greg.

--
With Regards,
Amit Kapila.