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Re: significant slow down with various LIMIT

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "norn" <andrey(dot)perliev(at)gmail(dot)com>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: significant slow down with various LIMIT
Date: 2010-04-14 14:31:33
Message-ID: 4BC58B75020000250003085F@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-performance
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
 
> (3) Try it like this (untested, so you may need to fix it up):
>  
> explain analyze
> SELECT core_object.id
>   from (SELECT id, city_id FROM "plugins_guide_address")
>        "plugins_guide_address"
>   JOIN "plugins_plugin_addr"
>     ON ("plugins_plugin_addr"."address_id"
>        = "plugins_guide_address"."id")
>   JOIN "core_object"
>     ON ("core_object"."id" = "plugins_plugin_addr"."oid_id")
>   WHERE "plugins_guide_address"."city_id" = 4535
>   ORDER BY "core_object"."id" DESC
>   LIMIT 4 -- or whatever it normally takes to cause the problem
> ;
 
Hmph.  I see I didn't take that quite where I intended.
Forget the above and try this:
 
explain analyze
SELECT core_object.id
  from (SELECT id, city_id FROM "plugins_guide_address"
          WHERE "city_id" = 4535) "plugins_guide_address"
  JOIN "plugins_plugin_addr"
    ON ("plugins_plugin_addr"."address_id"
       = "plugins_guide_address"."id")
  JOIN "core_object"
    ON ("core_object"."id" = "plugins_plugin_addr"."oid_id")
  ORDER BY "core_object"."id" DESC
  LIMIT 4 -- or whatever it normally takes to cause the problem
;
 
-Kevin

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