| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Florian Schoppmann <Florian(dot)Schoppmann(at)emc(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Invalid optimization of VOLATILE function in WHERE clause? |
| Date: | 2012-09-19 16:34:35 |
| Message-ID: | 29422.1348072475@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Sep 19, 2012 at 10:30 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> To do what you want, I'd suggest wrapping the join into a sub-select
>> with an "OFFSET 0" clause, which will serve as an optimization fence
>> that prevents the random() call from being pushed down.
> You've repeatedly objected to complaints on pgsql-performance on the
> grounds that WITH is an optimization fence. It seems awfully
> inconsistent to turn around and say, oh, sometimes it's not a fence
> after all.
Huh? The join in question is not inside a WITH. If it were, that
would work too, as noted by Merlin.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Robert Haas | 2012-09-19 16:55:26 | Re: Invalid optimization of VOLATILE function in WHERE clause? |
| Previous Message | Robert Haas | 2012-09-19 16:10:59 | Re: Invalid optimization of VOLATILE function in WHERE clause? |