HASH JOIN RIGHT SEMI

Question

Hi,
(Sorry) DB version is 11.2.0.2
I was trying to tune a sql using advisory. Present cost of the query is around 2100K. Advisory says to accept profile and the cost of the query will be around 7000.
But when sql profile is accepted the execution path of the query started doing 'HASH JOIN RIGHT SEMI' and the temp usage is so so high.
| Id  | Operation                                   | Name                   | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
|   0 | INSERT STATEMENT                            |                        |       |       |  1219G|  7142 (100)|          |
|   1 |  LOAD TABLE CONVENTIONAL                    |                        |       |       |  1219G|            |          |Because the temp usage is so high the temp tablespace keep growing and growing. How do i optimize this query?
thanks,
baskar.l
Edited by: baskar.l on Feb 26, 2012 10:05 PM

Answer 1

Hi Baskar,
cost of a SQL statement is not a very informative quantity. It's an estimate of how much resources would be consumed during the query's execution, not the actual figure.
You should look at actual rowsource statistics, not at optimizer estimates. Use gather_plan_statistics hint and then display using
select * from table(dbms_xplan.display_cursor(<sql_id>, null, 'allstats last'));and post results here.
Best regards,
Nikolay