A user receives the following error while executing a query：
ORA­01555：snapshot too old
Which two options can be the solutions to avoid such errors in future？（）

多项选择题User SCOTT executes the following command on the EMP table but has not issued COMMIT， ROLLBACK，or any data definition language （DDL） command：  SQL> SELECT job FROM emp  2  WHERE job=’CLERK’ FOR UPDATE OF empno  SCOTT has opened another session to work with the database. Which three operations would wait when issued in SCOTT’s second session？（）

A.LOCK TABLE emp IN SHARE MODE;
B.LOCK TABLE emp IN EXCLUSIVE MODE;
C.DELETE FROM emp WHERE job=’MANAGER’;
D.INSERT INTO emp（empno，ename） VALUES （1289，’Dick’）;
E.SELECT job FROM emp WHERE job=’CLERK’ FOR UPDATE OF empno;

多项选择题WhichtwoarevalidlockinglevelsthatareusedbytransactionsinanOracledatabase？（）

A.row level
B.block level
C.object level
D.schema level
E.database level

单项选择题The ST_INFO master table has millions of rows that are updated very rarely. It has a STATE_CODE column that contains the value for 25 states. The table is frequently queried on the STATE_CODE column.  Which type of index would you suggest to improve the query performance？（）

A.B­tree
B.bitmap
C.reverse key
D.function based

多项选择题AconstraintinatableisdefinedwiththeINITIALLYIMMEDIATEclause.YouexecutedtheALTERTABLEcommandwiththeENABLEVALIDATEoptiontoenabletheconstraintthatwasdisabled.Whatarethetwoeffectsofthiscommand？（）

A.It fails if any existing row violates the constraint.
B.It does not validate the existing data in the table.
C.It enables the constraint to be enforced at the end of each transaction.
D.It prevents insert， update， and delete operations on the table while the constraint is in the process of being enabled.

单项选择题Your database is started by using the server parameter file （SPFILE）. You issued this command to change the value of the LOG_BUFFER initialization parameter：  ALTER SYSTEM SET LOG_BUFFER=24M SCOPE=BOTH  What would be the outcome of this command？（）

A.The command would return an error because LOG_BUFFER is a static parameter.
B.The parameter value would be changed and it would come into effect immediately.
C.You need to restart the database so that parameter changes can come into effect.
D.The command would succeed only if initialization parameter LOG_ARCHIVE_MAX_PROCESS is set to value 2.