OPT_PARAM Hint

Applies to:
Oracle Server – Enterprise Edition – Version: 10.2.0.1 to 10.2.0.3 – Release: 10.2 to 10.2
Information in this document applies to any platform.
Goal
This article is explains the new optimizer hint “OPT_PARAM” introduced in 10g R2.
Solution
“OPT_PARAM” is a new optimizer hint introduced in 10g Release 2. This hint behaves the same way as
setting a parameter (e.g, using alter session) except that the effect is for the statement only. The hint only works for optimizer parameters. Global parameters such as optimizer_features_enable are not covered but optimizer_features_enable specifically has its own hint:

/*+ optimizer_features_enable(‘9.2.0’) */

@For an INTERNAL list of usable parameters see: Note:986618.1 Parameters useable by OPT_PARAM hint
Hint Syntax
The syntax is:

/*+ opt_param( [,] ) */

parameter_name is the name of a parameter
parameter_value is its value.

If the parameter contains a numeric value, the parameter value has to be specified without quotes.
The hint can be used to set multiple parameters by repeating the hint, i.e.

/*+ opt_param( [,] )
opt_param( [,] )
*/

Basic Usage Example
For example, the following hint sets <> to ‘false’ when added to a statement:

/*+ opt_param(‘hash_join_enabled’,’false’) */

e.g.:
Without the hint:


SQL> select empno from emp e, dept d where e.ename=d.dname

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     8 |   160 |     7  (15)| 00:00:01 |
|*  1 |  HASH JOIN         |      |     8 |   160 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| DEPT |     4 |    40 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| EMP  |    28 |   280 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

With the hint the hash join is disabled choosing a different plan:


SQL> select /*+ opt_param('hash_join_enabled','false') */ empno 
from emp e, dept d where e.ename=d.dname;


----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |     8 |   160 |     8  (25)| 00:00:01 |
|   1 |  MERGE JOIN         |      |     8 |   160 |     8  (25)| 00:00:01 |
|   2 |   SORT JOIN         |      |     4 |    40 |     4  (25)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| DEPT |     4 |    40 |     3   (0)| 00:00:01 |
|*  4 |   SORT JOIN         |      |    28 |   280 |     4  (25)| 00:00:01 |
|   5 |    TABLE ACCESS FULL| EMP  |    28 |   280 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------



Multiple Parameter Settings example
The OPT_PARAM hint can be specified more than once Time to adjust more than one parameter at once as follows:


/*+ OPT_PARAM('_always_semi_join' 'off')
      OPT_PARAM('_b_tree_bitmap_plans' 'false')
      OPT_PARAM('query_rewrite_enabled' 'false')
      OPT_PARAM('_new_initial_join_orders' 'false')
      OPT_PARAM('optimizer_dynamic_sampling' 1)
      OPT_PARAM('optimizer_index_cost_adj' 1) */

Comments

  1. Hi SlavikThis has come up on Twitter (and in private emlais before as well). UKOUG last tweet on the matter .@alexgorbachev – We are aware of the issues with the current system and are in the processing of sourcing a new tool for next year. You probably know this but the error you got (and the page extension!) only tells you the front end technology. You have to get database error message to know it’s not an Oracle DB. Unfortunately I’ve had one of those as well.

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