Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager

On Fri, Mar 13, 2020 at 8:42 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > On Thu, Mar 12, 2020 at 7:50 PM Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com> wrote:
> >
> > > + /*
> > > + * The relation extension or page lock can never participate in actual
> > > + * deadlock cycle. See Asserts in LockAcquireExtended. So, there is
> > > + * no advantage in checking wait edges from it.
> > > + */
> > > + if ((LOCK_LOCKTAG(*lock) == LOCKTAG_RELATION_EXTEND) ||
> > > + (LOCK_LOCKTAG(*lock) == LOCKTAG_PAGE))
> > > + return false;
> > > +
> > > Since this is true, we can also avoid these kind of locks in
> > > ExpandConstraints, right?
>
> I am not sure I understand this part. Because topological sort will
> work on the soft edges we have created when we found the cycle, but
> for relation extension/page lock we are completely ignoring hard/soft
> edge then it will never participate in topo sort as well. Am I
> missing something?
>
No, I think you're right. We only add constraints if we've detected a
cycle in the graph. Hence, you don't need the check here.

--
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com