Optimizer_mode set to CHOOSE in Oracle 10G

Question

I a bit confused about the new settings for the parameter "optimizer_mode" on 10G. If the parameter is set to CHOOSE on a 10G database, what value is the database actually using since CHOOSE is no longer a valid choice for this parameter (ALL_ROWS or FIRST_ROWS) ?
Thanks
John

Answer 1

database actually using since CHOOSE is no longer a
valid choice for this parameter (ALL_ROWS or
FIRST_ROWS) ?It is completely valid choice. It is deprecated yes and should not be used but see as follows:
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
SQL> alter system set optimizer_mode = choose scope=both;
System altered.
SQL> select user from dual;
USER
GINTS
SQL> create table bzzz as select * from dba_source;
Table created.
SQL> alter session set optimizer_dynamic_sampling = 0;
Session altered.
SQL> set autot on
SQL> select count(*) from bzzz;
  COUNT(*)
    280779
Execution Plan
Plan hash value: 2985757553
| Id  | Operation          | Name |
|   0 | SELECT STATEMENT   |      |
|   1 |  SORT AGGREGATE    |      |
|   2 |   TABLE ACCESS FULL| BZZZ |
Note
   - rule based optimizer used (consider using cbo)Gints Plivna
http://www.gplivna.eu