(Continued from previous part...)

Interview Questions for DBA (2)

11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not?
Level: High
Expected answer: You can?t use hot backup without being in archivelog mode. So no, you couldn?t recover.

12. What causes the "snapshot too old" error? How can this be prevented or mitigated?
Level: Intermediate
Expected answer: This is caused by large or long running transactions that have either wrapped onto their own rollback space or have had another transaction write on part of their rollback space. This can be prevented or mitigated by breaking the transaction into a set of smaller transactions or increasing the size of the rollback segments and their extents.

13. How can you tell if a database object is invalid?
Level: Low
Expected answer: By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account.

14. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check?
Level: Low
Expected answer: You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that points to the object (create synonym emp for scott.emp;)

15. A developer is trying to create a view and the database won?t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem?
Level: Intermediate
Expected answer: You need to verify the developer has direct grants on all tables used in the view. You can?t create a stored object with grants given through views.

16. If you have an example table, what is the best way to get sizing data for the production table implementation?
Level: Intermediate
Expected answer: The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.

17. How can you find out how many users are currently logged into the database? How can you find their operating system id?
Level: high
Expected answer: There are several ways. One is to look at the v$session or v$process views. Another way is to check the current_logins parameter in the v$sysstat view. Another if you are on UNIX is to do a "ps -ef|grep oracle|wc -l? command, but this only works against a single instance installation.

18. A user selects from a sequence and gets back two values, his select is:
SELECT pk_seq.nextval FROM dual;
What is the problem?
Level: Intermediate
Expected answer: Somehow two values have been inserted into the dual table. This table is a single row, single column table that should only have one value in it.

19. How can you determine if an index needs to be dropped and rebuilt?
Level: Intermediate
Expected answer: Run the ANALYZE INDEX command on the index to validate its structure and then calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near 1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio
BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3.

(Continued on next part...)