Re: Need help with one query

From: Tom Lane
Subject: Re: Need help with one query
Date: ,
Msg-id: 13823.1237562877@sss.pgh.pa.us
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In response to: Re: Need help with one query  (Richard Huxton)
List: pgsql-performance

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Need help with one query  (Anne Rosset, )
 Re: Need help with one query  (Richard Huxton, )
  Re: Need help with one query  (Tom Lane, )
  Re: Need help with one query  (Anne Rosset, )
   Re: Need help with one query  (Robert Haas, )
    Re: Need help with one query  (Alvaro Herrera, )
     Re: Need help with one query  (Anne Rosset, )
      Re: Need help with one query  (Robert Haas, )
    Re: Need help with one query  (Tom Lane, )
     Re: Need help with one query  (Anne Rosset, )
      Re: Need help with one query  (Robert Haas, )
       Re: Need help with one query  (Anne Rosset, )

Richard Huxton <> writes:
>> Hash Join  (cost=8.79..253664.55 rows=4 width=136) (actual
>> time=4612.674..6683.158 rows=4 loops=1)
>> Hash Cond: ((audit_change.audit_entry_id)::text = (audit_entry.id)::text)
>> ->  Seq Scan on audit_change  (cost=0.00..225212.52 rows=7584852
>> width=123) (actual time=0.009..2838.216 rows=7584852 loops=1)
>> ->  Hash  (cost=8.75..8.75 rows=3 width=45) (actual time=0.049..0.049
>> rows=4 loops=1)
>> ->  Index Scan using audit_entry_object on audit_entry
>> (cost=0.00..8.75 rows=3 width=45) (actual time=0.033..0.042 rows=4 loops=1)
>> Index Cond: ((object_id)::text = 'artf414029'::text)
>> Total runtime: 6683.220 ms

> Very odd. It knows the table is large and that the seq-scan is going to
> be expensive.

Yeah, *very* odd.  A nestloop with inner indexscan should have an
estimated cost far lower than this plan.  What Postgres version is
this exactly?  Do you have any nondefault planner parameter settings?

            regards, tom lane


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