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help / color / mirror / Atom feedFrom: Tom Lane <[email protected]>
To: Robert Haas <[email protected]>
Cc: Amit Langote <[email protected]>
Cc: Thom Brown <[email protected]>
Cc: Daniel Gustafsson <[email protected]>
Cc: Alvaro Herrera <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: David Rowley <[email protected]>
Cc: Jacob Champion <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: generic plans and "initial" pruning
Date: Mon, 07 Aug 2023 11:44:53 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+Tgmoan++3tDKjBysnp3QdJc_f+zKYFezXQw9jUPvRY=kZ9Cg@mail.gmail.com>
References: <[email protected]>
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Robert Haas <[email protected]> writes:
> Second, I wondered whether the ordering of cleanup operations could be
> an issue. Right now, a node can position cleanup code before, after,
> or both before and after recursing to child nodes, whereas with this
> design change, the cleanup code will always be run before recursing to
> child nodes. Here, I think we have problems. Both ExecGather and
> ExecEndGatherMerge intentionally clean up the children before the
> parent, so that the child shutdown happens before
> ExecParallelCleanup(). Based on the comment and commit
> acf555bc53acb589b5a2827e65d655fa8c9adee0, this appears to be
> intentional, and you can sort of see why from looking at the stuff
> that happens in ExecParallelCleanup().
Right, I doubt that changing that is going to work out well.
Hash joins might have issues with it too.
Could it work to make the patch force child cleanup before parent,
instead of after? Or would that break other places?
On the whole though I think it's probably a good idea to leave
parent nodes in control of the timing, so I kind of side with
your later comment about whether we want to change this at all.
regards, tom lane
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Subject: Re: generic plans and "initial" pruning
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