Horton

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

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Cc: 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: 2020-03-09T09:06:32Z
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 Mon, Mar 9, 2020 at 2:09 PM Masahiko Sawada <
masahiko.sawada@2ndquadrant.com> wrote:

> On Mon, 9 Mar 2020 at 15:50, Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Mon, Mar 9, 2020 at 11:38 AM Masahiko Sawada <
> masahiko.sawada@2ndquadrant.com> wrote:
> >>
> >> On Mon, 9 Mar 2020 at 14:16, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> >> >
> >> > On Sun, Mar 8, 2020 at 7:58 AM Masahiko Sawada <
> masahiko.sawada@2ndquadrant.com> wrote:
> >> >> >
> >> >> > Fair position, as per initial analysis, I think if we do below
> three
> >> >> > things, it should work out without changing to a new way of locking
> >> >> > for relation extension or page type locks.
> >> >> > a. As per the discussion above, ensure in code we will never try to
> >> >> > acquire another heavy-weight lock after acquiring relation
> extension
> >> >> > or page type locks (probably by having Asserts in code or maybe
> some
> >> >> > other way).
> >> >>
> >> >> The current patch
> >> >> (v02_0001-Added-assert-to-verify-that-we-never-try-to-take-any.patch)
> >> >> doesn't check that acquiring a heavy-weight lock after page type
> lock,
> >> >> is that right?
> >> >
> >> >
> >> > No, it should do that.
> >> >
> >> >>
> >> >> There is the path doing that: ginInsertCleanup() holds
> >> >> a page lock and insert the pending list items, which might hold a
> >> >> relation extension lock.
> >> >
> >> >
> >> > Right, I could also see that, but do you see any problem with that?
> I agree that Assert should cover this case, but I don't see any fundamental
> problem with that.
> >>
> >> I think that could be a problem if we change the group locking so that
> >> it doesn't consider page lock type.
> >
> >
> > I might be missing something, but won't that be a problem only when if
> there is a case where we acquire page lock after acquiring a relation
> extension lock?
>
> Yes, you're right.
>
> Well I meant that the reason why we need to make Assert should cover
> page locks case is the same as the reason for extension lock type
> case. If we change the group locking so that it doesn't consider
> extension lock and change deadlock so that it doesn't make a wait edge
> for it, we need to ensure that the same backend doesn't acquire
> heavy-weight lock after holding relation extension lock. These are
> already done in the current patch. Similarly, if we did the similar
> change for page lock in the group locking and deadlock , we need to
> ensure the same things for page lock.


Agreed.


> But ISTM it doesn't necessarily
> need to support page lock for now because currently we use it only for
> cleanup pending list of gin index.
>
>
I agree, but I think it is better to have a patch for the same even if we
want to review/commit that separately.  That will help us to look at how
the complete solution looks.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com