Re: Why hash join instead of nested loop?

From: Michael Fuhr
Subject: Re: Why hash join instead of nested loop?
Date: ,
Msg-id: 20050809051148.GA85494@winnie.fuhr.org
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In response to: Re: Why hash join instead of nested loop?  (Tom Lane)
List: pgsql-performance

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Why hash join instead of nested loop?  (Rhett Garber, )
 Re: Why hash join instead of nested loop?  (Havasvölgyi Ottó, )
  Re: Why hash join instead of nested loop?  (Rhett Garber, )
   Re: Why hash join instead of nested loop?  (Tom Lane, )
    Re: Why hash join instead of nested loop?  (Rhett Garber, )
     Re: Why hash join instead of nested loop?  (Tom Lane, )
      Re: Why hash join instead of nested loop?  ("Steinar H. Gunderson", )
      Re: Why hash join instead of nested loop?  (Michael Fuhr, )
      Re: Why hash join instead of nested loop?  (Ian Westmacott, )
       Re: Why hash join instead of nested loop?  (Tom Lane, )
        Re: Why hash join instead of nested loop?  (Ian Westmacott, )
      Re: Why hash join instead of nested loop?  (Rhett Garber, )
       Re: Why hash join instead of nested loop?  (Tom Lane, )
        Re: Why hash join instead of nested loop?  (Rhett Garber, )
         Re: Why hash join instead of nested loop?  (Tom Lane, )
          Re: Why hash join instead of nested loop?  (Rhett Garber, )
           Re: Why hash join instead of nested loop?  (Tom Lane, )
            Re: Why hash join instead of nested loop?  (Rhett Garber, )

On Mon, Aug 08, 2005 at 08:58:26PM -0400, Tom Lane wrote:
> I'd be interested to see results from other people using 7.4.* too.

I just built 7.4.1 on FreeBSD 4.11-STABLE and ran your test:

test=# explain analyze select rtmessagestate.* from rtmessagestate,connection where (connection_registry_id =  40105)
AND(obj1  = 73582) and id = obj2; 
                                                                     QUERY PLAN
                            

----------------------------------------------------------------------------------------------------------------------------------------------------
 Hash Join  (cost=4.83..5.91 rows=1 width=14) (actual time=0.220..0.264 rows=1 loops=1)
   Hash Cond: ("outer".id = "inner".obj2)
   ->  Seq Scan on rtmessagestate  (cost=0.00..1.05 rows=5 width=14) (actual time=0.015..0.050 rows=5 loops=1)
   ->  Hash  (cost=4.83..4.83 rows=1 width=4) (actual time=0.103..0.103 rows=0 loops=1)
         ->  Index Scan using connection_regid_obj1_index on connection  (cost=0.00..4.83 rows=1 width=4) (actual
time=0.070..0.081rows=1 loops=1) 
               Index Cond: ((connection_registry_id = 40105) AND (obj1 = 73582))
 Total runtime: 0.495 ms
(7 rows)

--
Michael Fuhr


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