| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | Jim Nasby <jim(at)nasby(dot)net>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, David Johnston <polobo(at)yahoo(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Planner hints in Postgresql |
| Date: | 2014-03-17 23:47:27 |
| Message-ID: | 11603.1395100047@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Claudio Freire <klaussfreire(at)gmail(dot)com> writes:
> On Mon, Mar 17, 2014 at 7:01 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
>> Even better would be if the planner could estimate how bad a plan will
>> become if we made assumptions that turn out to be wrong.
> That's precisely what risk estimation was about.
Yeah. I would like to see the planner's cost estimates extended to
include some sort of uncertainty estimate, whereupon risk-averse people
could ask it to prefer low-uncertainty plans over high-uncertainty ones
(the plans we typically choose for ORDER BY ... LIMIT queries being great
examples of the latter). But it's a long way from wishing that to making
it so. Right now it's not even clear (to me anyway) how we'd measure or
model such uncertainty.
regards, tom lane
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