Set - 1

Question 51 :

What is the effect of setting the value "CHOOSE" for OPTIMIZER_GOAL, parameter of the ALTER SESSION Command ?

Answer :

The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.


Question 52 :

How does one create a new database? (for DBA)

Answer :

One can create and modify Oracle databases using the Oracle "dbca" (Database Configuration Assistant) utility. The dbca utility is located in the $ORACLE_HOME/bin directory. The Oracle Universal Installer (oui) normally starts it after installing the database server software.
One can also create databases manually using scripts. This option, however, is falling out of fashion, as it is quite involved and error prone. Look at this example for creating and Oracle 9i database:

CONNECT SYS AS SYSDBA
ALTER SYSTEM SET DB_CREATE_FILE_DEST='/u01/oradata/';
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_1='/u02/oradata/';
ALTER SYSTEM SET DB_CREATE_ONLINE_LOG_DEST_2='/u03/oradata/';
CREATE DATABASE;

 


Question 53 :

What database block size should I use? (for DBA)

Answer :

Oracle recommends that your database block size match, or be multiples of your operating system block size. One can use smaller block sizes, but the performance cost is significant. Your choice should depend on the type of application you are running. If you have many small transactions as with OLTP, use a smaller block size. With fewer but larger transactions, as with a DSS application, use a larger block size. If you are using a volume manager, consider your "operating system block size" to be 8K. This is because volume manager products use 8K blocks (and this is not configurable).


Question 54 :

What are the different approaches used by Optimizer in choosing an execution plan ?

Answer :

Rule-based and Cost-based.


Question 55 :

What does ROLLBACK do ?

Answer :

ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.