Horton

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

Kuntal Ghosh <kuntalghosh.2007@gmail.com>

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From: Kuntal Ghosh <kuntalghosh.2007@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <masahiko.sawada@2ndquadrant.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Michael Paquier <michael@paquier.xyz>, Mithun Cy <mithun.cy@enterprisedb.com>, Thomas Munro <thomas.munro@enterprisedb.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2020-03-13T09:05:57Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Allow page lock to conflict among parallel group members.

  2. Allow relation extension lock to conflict among parallel group members.

  3. Add assert to ensure that page locks don't participate in deadlock cycle.

  4. Assert that we don't acquire a heavyweight lock on another object after

  5. Fix unsafe usage of strerror(errno) within ereport().

On Fri, Mar 13, 2020 at 8:42 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > On Thu, Mar 12, 2020 at 7:50 PM Kuntal Ghosh <kuntalghosh.2007@gmail.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