Re: Asynchronous execution on FDW

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Asynchronous execution on FDW
Date: 2015-08-10 20:03:50
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* Robert Haas (robertmhaas(at)gmail(dot)com) wrote:
> On Mon, Aug 10, 2015 at 3:23 AM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> > I've marked this as rejected in the commitfest, because others are
> > working on a more general solution with parallel workers. That's still
> > work-in-progress, and it's not certain if it's going to make it into
> > 9.6, but if it does it will largely render this obsolete. We can revisit
> > this patch later in the release cycle, if the parallel scan patch hasn't
> > solved the same use case by then.
> I think the really important issue for this patch is the one discussed here:

I agree that it'd be great to figure out the answer to #2, but I'm also
of the opinion that we can either let the user tell us through the use
of the GUCs proposed in the patch or simply not worry about the
potential for time wastage associated with starting them all at once, as
you suggested there.

> You raised an important issue there but never really expressed an
> opinion on the points I raised, here or on the other thread. And
> neither did anyone else except the patch author who, perhaps
> unsurprisingly, thinks it's OK. I wish we could get more discussion
> about that.

When I read the proposal, I had the same reaction that it didn't seem
like quite the right place and it further bothered me that it was
specific to FDWs.

Perhaps not surprisingly, as I authored it, but I'm still a fan of my
proposal #1 here:

More generally, I completely agree with the position (I believe your's,
but I might be misremembering) that we want to have this async
capability independently and in addition to parallel scan. I don't
believe one obviates the advantages of the other.



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