Re: Functionscan estimates

From: Tom Lane
Subject: Re: Functionscan estimates
Date: ,
Msg-id: 19038.1113019256@sss.pgh.pa.us
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In response to: Re: Functionscan estimates  (Alvaro Herrera)
Responses: Re: Functionscan estimates  (PFC)
Re: Functionscan estimates  ("Jim C. Nasby")
Re: Functionscan estimates  (Neil Conway)
List: pgsql-performance

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Functionscan estimates  (Josh Berkus, )
 Re: Functionscan estimates  (Michael Fuhr, )
  Re: Functionscan estimates  (Alvaro Herrera, )
   Re: Functionscan estimates  (Josh Berkus, )
    Re: Functionscan estimates  (Alvaro Herrera, )
     Re: Functionscan estimates  (Tom Lane, )
      Re: Functionscan estimates  (PFC, )
      Re: Functionscan estimates  ("Jim C. Nasby", )
       Re: Functionscan estimates  (Tom Lane, )
        Re: Functionscan estimates  (Neil Conway, )
         Re: Functionscan estimates  (Josh Berkus, )
      Re: Functionscan estimates  (Neil Conway, )
    Re: Functionscan estimates  (PFC, )

Not too many releases ago, there were several columns in pg_proc that
were intended to support estimation of the runtime cost and number of
result rows of set-returning functions.  I believe in fact that these
were the remains of Joe Hellerstein's thesis on expensive-function
evaluation, and are exactly what he was talking about here:
http://archives.postgresql.org/pgsql-hackers/2002-06/msg00085.php

But with all due respect to Joe, I think the reason that stuff got
trimmed is that it didn't work very well.  In most cases it's
*hard* to write an estimator for a SRF.  Let's see you produce
one for dblink() for instance ...

            regards, tom lane


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