Horton

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

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Mithun Cy <mithun.cy@enterprisedb.com>, Tom Lane <tgl@sss.pgh.pa.us>, Thomas Munro <thomas.munro@enterprisedb.com>, Amit Kapila <amit.kapila16@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-04-10T09:40:54Z
Lists: pgsql-hackers

Commits

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  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 30, 2018 at 4:43 PM, Michael Paquier <michael@paquier.xyz> wrote:
> On Thu, Mar 01, 2018 at 04:01:28PM -0500, Robert Haas wrote:
>> If you have a clever idea how to make this work with as few atomic
>> operations as the current patch uses while at the same time reducing
>> the possibility of contention, I'm all ears.  But I don't see how to
>> do that.
>
> This thread has no activity since the beginning of the commit fest, and
> it seems that it would be hard to reach something committable for v11,
> so I am marking it as returned with feedback.

Thank you.

The probability of performance degradation can be reduced by
increasing N_RELEXTLOCK_ENTS. But as Robert mentioned, while keeping
fast and simple implementation like acquiring lock by a few atomic
operation it's hard to improve or at least keep the current
performance on all cases. I was thinking that this patch is necessary
by parallel DML operations and vacuum but if the community cannot
accept this approach it might be better to mark it as "Rejected" and
then I should reconsider the design of parallel vacuum.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center