Re: Any better plan for this query?..

From: Matthew Wakeling
Subject: Re: Any better plan for this query?..
Date: ,
Msg-id: alpine.DEB.2.00.0905061030590.2341@aragorn.flymine.org
(view: Whole thread, Raw)
In response to: Re: Any better plan for this query?..  (Heikki Linnakangas)
List: pgsql-performance

Tree view

Any better plan for this query?..  (Dimitri, )
 Re: Any better plan for this query?..  (Craig Ringer, )
  Re: Any better plan for this query?..  (Dimitri, )
   Re: Any better plan for this query?..  (Chris, )
    Re: Any better plan for this query?..  (Dimitri, )
     Re: Any better plan for this query?..  (Richard Huxton, )
     Re: Any better plan for this query?..  (Craig Ringer, )
      Re: Any better plan for this query?..  (Kenneth Marshall, )
       Re: Any better plan for this query?..  (Matthew Wakeling, )
      Re: Any better plan for this query?..  (Dimitri, )
  Re: Any better plan for this query?..  (Kenneth Marshall, )
 Re: Any better plan for this query?..  (Heikki Linnakangas, )
  Re: Any better plan for this query?..  (Dimitri, )
   Re: Any better plan for this query?..  (Simon Riggs, )
    Re: Any better plan for this query?..  (Dimitri, )
     Re: Any better plan for this query?..  (Merlin Moncure, )
      Re: Any better plan for this query?..  (Dimitri, )
       Re: Any better plan for this query?..  (Simon Riggs, )
        Re: Any better plan for this query?..  (Dimitri, )
         Re: Any better plan for this query?..  (Tom Lane, )
          Re: Any better plan for this query?..  (Dimitri, )
          Re: Any better plan for this query?..  (Simon Riggs, )
         Re: Any better plan for this query?..  (Merlin Moncure, )
         Re: Any better plan for this query?..  (Simon Riggs, )
          Re: Any better plan for this query?..  (Dimitri, )
         Re: Any better plan for this query?..  (Aidan Van Dyk, )
          Re: Any better plan for this query?..  (Dimitri, )
           Re: Any better plan for this query?..  (Alvaro Herrera, )
            Re: Any better plan for this query?..  (Dimitri, )
             Re: Any better plan for this query?..  (Dimitri Fontaine, )
              Re: Any better plan for this query?..  (Dimitri, )
               Re: Any better plan for this query?..  (Simon Riggs, )
                Re: Any better plan for this query?..  (Dimitri, )
                 Re: Any better plan for this query?..  (Simon Riggs, )
               Re: Any better plan for this query?..  (Heikki Linnakangas, )
                Re: Any better plan for this query?..  (Dimitri, )
                 Re: Any better plan for this query?..  (Simon Riggs, )
                  Re: Any better plan for this query?..  (Dimitri, )
                   Re: Any better plan for this query?..  (Simon Riggs, )
                    Re: Any better plan for this query?..  (Dimitri, )
                     Re: Any better plan for this query?..  (Simon Riggs, )
                      Re: Any better plan for this query?..  ("Dave Dutcher", )
                       Re: Any better plan for this query?..  (Dimitri, )
                        Re: Any better plan for this query?..  (Merlin Moncure, )
                         Re: Any better plan for this query?..  (Dimitri, )
                          Re: Any better plan for this query?..  (Merlin Moncure, )
                           Re: Any better plan for this query?..  (Dimitri, )
                            Re: Any better plan for this query?..  (Merlin Moncure, )
                      Re: Any better plan for this query?..  (Dimitri, )
                       Re: Any better plan for this query?..  (Simon Riggs, )
                        Re: Any better plan for this query?..  (Dimitri, )
                         Re: Any better plan for this query?..  (Dimitri, )
                          Re: Any better plan for this query?..  (Simon Riggs, )
                           Re: Any better plan for this query?..  (Dimitri, )
                      Re: Any better plan for this query?..  (Tom Lane, )
                       Re: Any better plan for this query?..  (Dimitri, )
                       Re: Any better plan for this query?..  (Simon Riggs, )
                        Re: Any better plan for this query?..  (Matthew Wakeling, )
                         Re: Any better plan for this query?..  (Simon Riggs, )
                          Re: Any better plan for this query?..  (Simon Riggs, )
                          Re: Any better plan for this query?..  (Matthew Wakeling, )
                           Re: Any better plan for this query?..  (Simon Riggs, )
                           Re: Any better plan for this query?..  (Scott Carey, )
                          Re: Any better plan for this query?..  (Robert Haas, )
                        Re: Any better plan for this query?..  (Tom Lane, )
                         Re: Any better plan for this query?..  (Simon Riggs, )
                          Re: Any better plan for this query?..  (Tom Lane, )
                           Re: Any better plan for this query?..  (Robert Haas, )
                            Re: Any better plan for this query?..  (Simon Riggs, )
                             Re: Any better plan for this query?..  (Robert Haas, )
                              Re: Any better plan for this query?..  (Simon Riggs, )
                     Re: Any better plan for this query?..  (Scott Carey, )
                      Re: Any better plan for this query?..  (Dimitri, )
                       Re: Any better plan for this query?..  (Scott Carey, )
                        Re: Any better plan for this query?..  (Dimitri, )
                         Re: Any better plan for this query?..  (Scott Carey, )
                          Re: Any better plan for this query?..  (Dimitri, )
               Re: Any better plan for this query?..  (Simon Riggs, )
                Re: Any better plan for this query?..  (Dimitri, )
                 Re: Any better plan for this query?..  (Robert Haas, )
                  Re: Any better plan for this query?..  (Dimitri, )
                   Re: Any better plan for this query?..  ("Kevin Grittner", )
                   Re: Any better plan for this query?..  ("Joshua D. Drake", )
                    Re: Any better plan for this query?..  (Dimitri, )
                   Re: Any better plan for this query?..  (Robert Haas, )
                    Re: Any better plan for this query?..  (Dimitri, )
               Re: Any better plan for this query?..  (Stefan Kaltenbrunner, )
                Re: Any better plan for this query?..  (Dimitri, )
                 Re: Any better plan for this query?..  (Stefan Kaltenbrunner, )
                  Re: Any better plan for this query?..  (Matthew Wakeling, )
                   Re: Any better plan for this query?..  (Simon Riggs, )
                    Re: Any better plan for this query?..  (Matthew Wakeling, )
                     Re: Any better plan for this query?..  (Stefan Kaltenbrunner, )
                     Re: Any better plan for this query?..  (Tom Lane, )
                      Re: Any better plan for this query?..  (Robert Haas, )
                  Re: Any better plan for this query?..  (Dimitri, )
   Re: Any better plan for this query?..  ("Joshua D. Drake", )
           Re: Any better plan for this query?..  (Heikki Linnakangas, )
            Re: Any better plan for this query?..  (Dimitri, )
           Re: Any better plan for this query?..  (Andres Freund, )
            Re: Any better plan for this query?..  (Alvaro Herrera, )
             Re: Any better plan for this query?..  (Scott Carey, )
              Re: Any better plan for this query?..  (Dimitri, )
               Re: Any better plan for this query?..  (Scott Carey, )
                Re: Any better plan for this query?..  (Dimitri Fontaine, )
                 Re: Any better plan for this query?..  (Dimitri, )
                 Re: Any better plan for this query?..  (Simon Riggs, )
                Re: Any better plan for this query?..  (Dimitri, )
    Re: Any better plan for this query?..  (Gregory Stark, )
     Re: Any better plan for this query?..  (Simon Riggs, )
  Re: Any better plan for this query?..  (Matthew Wakeling, )
  Re: Any better plan for this query?..  (Tom Lane, )
   Re: Any better plan for this query?..  (Greg Stark, )
   Re: Any better plan for this query?..  (Robert Haas, )
  Re: Any better plan for this query?..  (Simon Riggs, )
   Re: Any better plan for this query?..  ("Joshua D. Drake", )
    Re: Any better plan for this query?..  (Aidan Van Dyk, )
     Re: Any better plan for this query?..  (Stephen Frost, )
   Re: Any better plan for this query?..  (Robert Haas, )
   Re: Any better plan for this query?..  (Glenn Maynard, )
    Re: Any better plan for this query?..  (Dimitri, )
    Re: Any better plan for this query?..  ("Kevin Grittner", )
     Re: Any better plan for this query?..  (Dimitri, )
      Re: Any better plan for this query?..  ("Kevin Grittner", )
  Re: Any better plan for this query?..  (Dimitri Fontaine, )
   Re: Any better plan for this query?..  (Alvaro Herrera, )
  Re: Any better plan for this query?..  (Robert Haas, )
   Re: Any better plan for this query?..  (Dimitri, )
 Re: Any better plan for this query?..  (Dimitri, )
  Re: Any better plan for this query?..  (Richard Huxton, )
  Re: Any better plan for this query?..  ("Albe Laurenz", )
   Re: Any better plan for this query?..  (Dimitri, )
    Re: Any better plan for this query?..  (Kenneth Marshall, )
 Re: Any better plan for this query?..  (Merlin Moncure, )
  Re: Any better plan for this query?..  (Merlin Moncure, )
   Re: Any better plan for this query?..  (Dimitri, )
    Re: Any better plan for this query?..  (Richard Huxton, )
     Re: Any better plan for this query?..  (Ries van Twisk, )
      Re: Any better plan for this query?..  (Dimitri, )
 Re: Any better plan for this query?..  (Kenneth Marshall, )
  Re: Any better plan for this query?..  (Dimitri, )
   Re: Any better plan for this query?..  (Kenneth Marshall, )
 Re: Any better plan for this query?..  (Dimitri, )
  Re: Any better plan for this query?..  (Alvaro Herrera, )
 Re: Any better plan for this query?..  (Simon Riggs, )

On Wed, 6 May 2009, Heikki Linnakangas wrote:
>>  Total runtime: 1.442 ms

It's pretty clear that this query isn't even going to disc - it's all CPU
time. That can be the case if you run the exact same query more than once,
and it can cause your EXPLAIN output to be vastly different from your real
use case. Do the queries on the live system hit the disc at all?

> The bad doesn't look too bad to me, although the planner is over-estimating
> the number of matches in the history table (2404 vs 20). That's a bit
> surprising given how simple the predicate is. Make sure you've ANALYZEd the
> table. If that's not enough, you can try to increase the statistics target
> for ref_object column, ie. ALTER TABLE history ALTER COLUMN ref_object SET
> STATISTICS 500.

I would have thought this would actually make it slower, by increasing the
time taken to plan. On such small queries, the planner overhead must be
quite significant.

Matthew

--
 Q: What's the difference between ignorance and apathy?
 A: I don't know, and I don't care.


pgsql-performance by date:

From: Dimitri
Date:
Subject: Re: Any better plan for this query?..
From: Kenneth Marshall
Date:
Subject: Re: Any better plan for this query?..