sridhar bamandlapally, 27.01.2012 05:31:
SQL> explain plan for select * from hr.emp ;
Explained.
PLAN
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 7444K| 944M| 16077 (4)| 00:03:13 |
| 1 | TABLE ACCESS FULL| EMP | 7444K| 944M| 16077 (4)| 00:03:13 |
--------------------------------------------------------------------------
*WITH PARALLEL Option*
SQL> explain plan for select /*+parallel(emp,4)*/ * from hr.emp ;
Explained.
PLAN
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 7444K| 944M| 4442 (3)| 00:00:54
|
| 1 | PX COORDINATOR | | | | |
|
| 2 | PX SEND QC (RANDOM)| :TQ10000 | 7444K| 944M| 4442 (3)| 00:00:54
|
| 3 | PX BLOCK ITERATOR | | 7444K| 944M| 4442 (3)| 00:00:54
|
| 4 | TABLE ACCESS FULL| EMP | 7444K| 944M| 4442 (3)| 00:00:54
|
---------------------------------------------------------------------------------
In the above plan ( WITH PARALLEL Option )
1. "Cost" has been nearly reduced to 1/4th
2. "CPU" has been reduced
3. "Time" has been nearly reduced to 1/3rd
I have *never* seen the "time" column in the explain plan output come anywhere
near the actual execution time in Oracle.
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