From: | Douglas Doole <dougdoole(at)gmail(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [PATCH] Push limit to sort through a subquery |
Date: | 2017-08-23 22:55:45 |
Message-ID: | CADE5jYLQEwxDFHVYRqDnkZQJqCBSs+Hj9s4nMjijO=3L_AJXdg@mail.gmail.com |
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>
> Buildfarm members with force_parallel_mode=regress are failing now. I
> haven't had a chance to investigate exactly what's going on here, but
> I think there are probably several issues:
>
Not an auspicious beginning for my first patch :-(
> 3. However, even if it did that, it would only affect the leader, not
> the workers, because each worker will of course have a separate copy
> of each executor state node. We could fix that by having the Gather
> or Gather Merge node also store the bound and propagate that to each
> worker via DSM, and then have each worker call pass_down_bound itself.
> (This would require a bit of refactoring of the API for
> pass_down_bound, but it looks doable.)
>
From previous experience, pushing the limit to the workers has the
potential to be a big win .
In the short run, I'm not sure we have a better alternative than
> removing this test - unless somebody has a better idea? - but it would
> be good to work on all of the above problems.
>
I haven't played with parallel mode at all yet. Is it possible to disable
force_parallel_mode for the new test? If not, then I'd agree that removing
the test is probably the only reasonable short term fix.
- Doug
Salesforce
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