| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Matthew Wakeling <matthew(at)flymine(dot)org> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Really dumb planner decision |
| Date: | 2009-04-16 16:04:40 |
| Message-ID: | 19203.1239897880@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Matthew Wakeling <matthew(at)flymine(dot)org> writes:
> On Thu, 16 Apr 2009, Robert Haas wrote:
>> I hasten to point out that I only suggested raising them to the moon
>> as a DEBUGGING strategy, not a production configuration.
> The problem is that we have created a view that by itself a very
> time-consuming query to answer, relying on it being incorporated into a
> query that will constrain it and cause it to be evaluated a lot quicker.
> This kind of scenario kind of guarantees a bad plan as soon as the number
> of tables reaches from_collapse_limit.
Well, if the payoff for you exceeds the extra planning time, then you
raise the setting. That's why it's a configurable knob. I was just
pointing out that there are downsides to raising it further than
absolutely necessary.
regards, tom lane
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