Re: Why hash join instead of nested loop?

On Mon, Aug 08, 2005 at 08:58:26PM -0400, Tom Lane wrote:
> Hmph.  There is something really strange going on here.  I tried to
> duplicate your problem in 7.4.*, thus:

PostgreSQL 7.4.7 (Debian sarge):

<create table and stuff, exactly the same as you>

regression=# 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=0.155..0.159 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=0.003..0.006 rows=5 loops=1)
   ->  Hash  (cost=4.83..4.83 rows=1 width=4) (actual time=0.026..0.026 rows=0 loops=1)
         ->  Index Scan using connection_regid_obj1_index on connection  (cost=0.00..4.83 rows=1 width=4) (actual
time=0.011..0.012rows=1 loops=1) 
               Index Cond: ((connection_registry_id = 40105) AND (obj1 = 73582))
 Total runtime: 0.215 ms
(7 rows)

This is an Opteron (in 32-bit mode), though.

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