Re: [PERFORM] Bad n_distinct estimation; hacks suggested?

From: Tom Lane
Subject: Re: [PERFORM] Bad n_distinct estimation; hacks suggested?
Date: ,
Msg-id: 10257.1114405167@sss.pgh.pa.us
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In response to: Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus)
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Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
 Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
 Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  ("Andrew Dunstan", )
 Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Tom Lane, )
  Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Andrew Dunstan, )
   Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
   Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
    Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Tom Lane, )
  Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Marko Ristola, )
  Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Simon Riggs, )
   Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
   Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Andrew Dunstan, )
 Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Simon Riggs, )
  Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Tom Lane, )
   Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Simon Riggs, )
    Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
     Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
     Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Andrew Dunstan, )
      Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Mischa Sandberg, )
       Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Andrew Dunstan, )
        Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
         Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Mischa Sandberg, )
         Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Markus Schaber, )
          Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Mischa Sandberg, )
           Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
            Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Josh Berkus, )
            Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Mischa Sandberg, )
            Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (John A Meinel, )
        Re: [PERFORM] Distinct-Sampling (Gibbons paper) for Postgres  (Josh Berkus, )
        Re: Distinct-Sampling (Gibbons paper) for Postgres  (, )
    Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Tom Lane, )
     Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Simon Riggs, )
      Re: [PERFORM] Bad n_distinct estimation; hacks suggested?  (Gurmeet Manku, )
      Citation for "Bad n_distinct estimation; hacks suggested?"  (Gurmeet Manku, )

Josh Berkus <> writes:
> Tom, how does our heuristic sampling work?   Is it pure random sampling, or
> page sampling?

Manfred probably remembers better than I do, but I think the idea is
to approximate pure random sampling as best we can without actually
examining every page of the table.

            regards, tom lane


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