| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Pushdown target list below gather node (WAS Re: WIP: Upper planner pathification) |
| Date: | 2016-03-16 18:02:43 |
| Message-ID: | 8245.1458151363@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Mar 16, 2016 at 12:57 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Yeah, I was thinking about the same thing. The comment block above
>> where you're looking would need some adjustment.
> OK, how about this?
Looks pretty close. One point is that if we do end up using a Result
node, then the parent GatherPath does not get charged for the Result
node's cpu_per_tuple overhead. I'm not sure that that's worth changing
though. It's probably better to bet that the subpath is projectable and
so no cost will ensue, than to bet the other way.
regards, tom lane
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