Slow response on data dictionary queries with optimizer_mode=rule in 10g

Question

I have two dataabse: DB1 (9i) and DB2 (10g) on windows 2000
They are two development databases with the same schemas and same tables. The application executes the same commands but with different results and execution plans.
In DB2 the queries with the most slow response tima are the queries on the data dictionary (for example: all_synonyms).
These query are very fast with the optimizer_mode=cost and very slow with the optimizer_mode=rule.
And the the problem is this:
in DB1 and DB2 the application executes after the connection this command:
ALTER SESSION SET OPTIMIZER_MODE = 'RULE';
These are the traces of the session in db1 and db2:
The queries are created dynamically by the application.
Is there a solution for this?
thanks
Message was edited by:
user596611

Answer 1

Here is a simple example of what can happen,
@>alter session set optimizer_mode=all_rows;
@>SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());
PLAN_TABLE_OUTPUT
| Id  | Operation        | Name | Rows  | Cost (%CPU)|
|   0 | SELECT STATEMENT |      |     1 |     2   (0)|
|   1 |  FAST DUAL       |      |     1 |     2   (0)|
@>alter session set optimizer_mode=rule;
@>SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY());
PLAN_TABLE_OUTPUT
| Id  | Operation        | Name |
|   0 | SELECT STATEMENT |      |
|   1 |  FAST DUAL       |      |
Note
      - rule based optimizer used (consider using cbo)As you can see incomplete explain plans. Therefore it is not advised.
Adith