Excerpts from Robert Haas's message of mié dic 29 09:17:17 -0300 2010: > On Tue, Dec 28, 2010 at 5:13 AM, Jie Li <jay23j...@gmail.com> wrote: > > Hi, > > > > Please see the following plan: > > > > postgres=# explain select * from small_table left outer join big_table using > > (id); > > QUERY PLAN > > ---------------------------------------------------------------------------- > > Hash Left Join (cost=126408.00..142436.98 rows=371 width=12) > > Hash Cond: (small_table.id = big_table.id) > > -> Seq Scan on small_table (cost=0.00..1.09 rows=9 width=8) > > -> Hash (cost=59142.00..59142.00 rows=4100000 width=8) > > -> Seq Scan on big_table (cost=0.00..59142.00 rows=4100000 > > width=8) > > (5 rows) > > > > Here I have a puzzle, why not choose the small table to build hash table? It > > can avoid multiple batches thus save significant I/O cost, isn't it? > > Yeah, you'd think. Can you post a full reproducible test case?
Also, what version is this? -- Álvaro Herrera <alvhe...@commandprompt.com> The PostgreSQL Company - Command Prompt, Inc. PostgreSQL Replication, Consulting, Custom Development, 24x7 support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
