Re: Really dumb planner decision

From: Tom Lane
Subject: Re: Really dumb planner decision
Date: ,
Msg-id: 19203.1239897880@sss.pgh.pa.us
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In response to: Re: Really dumb planner decision  (Matthew Wakeling)
List: pgsql-performance

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Really dumb planner decision  (Matthew Wakeling, )
 Re: Really dumb planner decision  (Grzegorz Jaśkiewicz, )
  Re: Really dumb planner decision  (Matthew Wakeling, )
   Re: Really dumb planner decision  (Robert Haas, )
    Re: Really dumb planner decision  (Matthew Wakeling, )
     Re: Really dumb planner decision  (Merlin Moncure, )
      Re: Really dumb planner decision  (Tom Lane, )
       Re: Really dumb planner decision  ("Kevin Grittner", )
        Re: Really dumb planner decision  (Merlin Moncure, )
       Re: Really dumb planner decision  (Robert Haas, )
        Re: Really dumb planner decision  (Matthew Wakeling, )
         Re: Really dumb planner decision  (Tom Lane, )
 Re: Really dumb planner decision  (Grzegorz Jaśkiewicz, )
  Re: Really dumb planner decision  (Matthew Wakeling, )

Matthew Wakeling <> 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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