| From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Craig Ringer <craig(at)2ndQuadrant(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, David Greco <David_Greco(at)harte-hanks(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Poor performance using CTE |
| Date: | 2012-11-21 13:04:38 |
| Message-ID: | 50ACD166.1000507@vmware.com |
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| Lists: | pgsql-performance |
On 21.11.2012 01:53, Tom Lane wrote:
> I think the more interesting question is what cases wouldn't be covered
> by such a rule. Typically you need to use OFFSET 0 in situations where
> the planner has guessed wrong about costs or rowcounts, and I think
> people are likely using WITH for that as well. Should we be telling
> people that they ought to insert OFFSET 0 in WITH queries if they want
> to be sure there's an optimization fence?
Yes, I strongly feel that we should. Writing a query using WITH often
makes it more readable. It would be a shame if people have to refrain
from using it, because the planner treats it as an optimization fence.
- Heikki
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