What will be my optimizer after importing 9iR2 to 10gR2 CBO or RBO?

Question

Friends,
OS: RHEL AS 3
what will be my optimizer after importing 9iR2 to 10gR2?
will it be in RBO or CBO?
What are the precautionary steps should i follow for the optimizer part?
thanks

Answer 1

The default optimizer , as mentioned already will be CBO based. Oracle would go for All_rows as the one.
RBO is still there ,even in 11g its there but oracle won't be accepting any bug reports or wont supply anything for issues about it. So if your stats are okay than it wil be cbo otherwise it will be RBO that would be kicking in,
Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, Oracle Label Security, OLAP, Data Mining,
Oracle Database Vault and Real Application Testing options
SQL> set auot trace exp
SP2-0158: unknown SET option "auot"
SQL> set autot trace exp
SQL> alter session set optimizer_mode=choose;
Session altered.
SQL> create table t( a char);
Table created.
SQL> select * from t;
Execution Plan
Plan hash value: 1601196873
| Id  | Operation         | Name |
|   0 | SELECT STATEMENT  |      |
|   1 |  TABLE ACCESS FULL| T    |
Note
   - rule based optimizer used (consider using cbo)
SQL> create table iot(a number primary key) organization index;
Table created.
SQL> select * from iot;
Execution Plan
Plan hash value: 3063468998
| Id  | Operation            | Name              | Rows  | Bytes | Cost (%CPU)|
Time     |
|   0 | SELECT STATEMENT     |                   |     1 |    13 |     2   (0)|
00:00:01 |
|   1 |  INDEX FAST FULL SCAN| SYS_IOT_TOP_71833 |     1 |    13 |     2   (0)|
00:00:01 |
Note
   - dynamic sampling used for this statement
SQL> select * from t,iot;
Execution Plan
Plan hash value: 3684863450
| Id  | Operation              | Name              | Rows  | Bytes | Cost (%CPU)
| Time     |
|   0 | SELECT STATEMENT       |                   |     1 |    16 |     4   (0)
| 00:00:01 |
|   1 |  MERGE JOIN CARTESIAN  |                   |     1 |    16 |     4   (0)
| 00:00:01 |
|   2 |   TABLE ACCESS FULL    | T                 |     1 |     3 |     2   (0)
| 00:00:01 |
|   3 |   BUFFER SORT          |                   |     1 |    13 |     2   (0)
| 00:00:01 |
|   4 |    INDEX FAST FULL SCAN| SYS_IOT_TOP_71833 |     1 |    13 |     2   (0)
| 00:00:01 |
Note
   - dynamic sampling used for this statement
SQL>You can see that with a simple table,T , without stats, RBO is coming but with IOT,which is a somewhat new object to RBO, CBO is kicking in.When both combined together, CBO is coming up.
If you would analyze the table, T CBO would come in.
You should check after upgrade those queries with a keen eye who are using RBO hint and are doing some index scans in RBO. They might change the behaviour after theupgrade.
HTH
Aman....