Horton

Re: Explain buffers wrong counter with parallel plans

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Adrien Nayrat <adrien.nayrat@anayrat.info>, Andres Freund <andres@anarazel.de>, PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Date: 2018-07-06T19:14:01Z
Lists: pgsql-hackers 
On Fri, Jul 6, 2018 at 9:44 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> I have tried this idea, but it doesn't completely solve the problem.
> The problem is that nodes below LIMIT won't get a chance to accumulate
> the stats as they won't be able to call InstrStopNode.

I'm not sure I understand.  Why not?  I see that we'd need to insert
an extra call to InstrStopNode() if we were stopping the node while it
was running, because then InstrStartNode() would have already been
done, but the corresponding call to InstrStopNode() would not have
been done.  But I'm not sure how that would happen in this case.  Can
you explain further?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Adjust comment atop ExecShutdownNode.

  2. Prohibit shutting down resources if there is a possibility of back up.

  3. Fix buffer usage stats for parallel nodes.

  4. Match the buffer usage tracking for leader and worker backends.

  5. Improve division of labor between execParallel.c and nodeGather[Merge].c.