On Sat, 23 Mar 2019 at 19:42, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <david.rowley@2ndquadrant.com> writes:
> > On Sat, 23 Mar 2019 at 05:40, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> BTW, another thing we could possibly do to answer this objection is to
> >> give the ordered-Append node an artificially pessimistic startup cost,
> >> such as the sum or the max of its children's startup costs. That's
> >> pretty ugly and unprincipled, but maybe it's better than not having the
> >> ability to generate the plan shape at all?
>
> > I admit to having thought of that while trying to get to sleep last
> > night, but I was too scared to even suggest it. It's pretty much how
> > MergeAppend would cost it anyway. I agree it's not pretty to lie
> > about the startup cost, but it does kinda seem silly to fall back on a
> > more expensive MergeAppend when we know fine well Append is cheaper.
>
> Yeah. I'm starting to think that this might actually be the way to go,
Here's a version with it done that way.
--
David Rowley http://www.2ndQuadrant.com/
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