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Oracle

Posted Dec 12, 2003

Oracle Technical Interview Questions Answered - Part2

By James Koopmann

This is the second part of the two part series on helping you answer those tough questions that you might experience in your quest for an Oracle DBA position.

The Oracle Technical Interview can be quite daunting. You never quite know what to study for and how to prepare. I am fully aware of this, as I have received many emails since my original article on interview questions was released. While these questions are only guidelines as to what should and more than likely will be asked, I hope that you find some comfort in the review of them. As always, do not just memorize the answers, as there are jewels to be found in the quest of figuring out the answer from the question. As always, remember that as you go through the article, it is not enough to know the answer to a particular question; you must try to put yourself in an interview situation and experience answering the question for yourself. Therefore, after you have gone through the questions and answers read the question again and then answer it with your own words. As always, good luck, and cheers.

Technical - Oracle

Last time, we answered questions 1 thru 20 of the technical part of the interview. Here are the next 30 in this section. Depending on the mood of the interview and your ability to elaborate on the answer, try to give some insight that you know more than just the simple answer to some of these questions. Also, be sensitive to the interviewer getting tired of you talking too much. Well here they are.

21.  How would you determine the time zone under which a database was operating?

select DBTIMEZONE from dual;

22.  Explain the use of setting GLOBAL_NAMES equal to TRUE.

Setting GLOBAL_NAMES dictates how you might connect to a database. This variable is either TRUE or FALSE and if it is set to TRUE it enforces database links to have the same name as the remote database to which they are linking.

23.  What command would you use to encrypt a PL/SQL application?

WRAP

24.  Explain the difference between a FUNCTION, PROCEDURE and PACKAGE.

A function and procedure are the same in that they are intended to be a collection of PL/SQL code that carries a single task. While a procedure does not have to return any values to the calling application, a function will return a single value. A package on the other hand is a collection of functions and procedures that are grouped together based on their commonality to a business function or application.

25.  Explain the use of table functions.

Table functions are designed to return a set of rows through PL/SQL logic but are intended to be used as a normal table or view in a SQL statement. They are also used to pipeline information in an ETL process.

26.  Name three advisory statistics you can collect.

Buffer Cache Advice, Segment Level Statistics, & Timed Statistics

27.  Where in the Oracle directory tree structure are audit traces placed?

In unix $ORACLE_HOME/rdbms/audit, in Windows the event viewer

28.  Explain materialized views and how they are used.

Materialized views are objects that are reduced sets of information that have been summarized, grouped, or aggregated from base tables. They are typically used in data warehouse or decision support systems.

29.  When a user process fails, what background process cleans up after it?

PMON

30.  What background process refreshes materialized views?

The Job Queue Processes.

31.  How would you determine what sessions are connected and what resources they are waiting for?

Use of V$SESSION and V$SESSION_WAIT

32.  Describe what redo logs are.

Redo logs are logical and physical structures that are designed to hold all the changes made to a database and are intended to aid in the recovery of a database.

33.  How would you force a log switch?

ALTER SYSTEM SWITCH LOGFILE;

34.  Give two methods you could use to determine what DDL changes have been made.

You could use Logminer or Streams

35.  What does coalescing a tablespace do?

Coalescing is only valid for dictionary-managed tablespaces and de-fragments space by combining neighboring free extents into large single extents.

36.  What is the difference between a TEMPORARY tablespace and a PERMANENT tablespace?

A temporary tablespace is used for temporary objects such as sort structures while permanent tablespaces are used to store those objects meant to be used as the true objects of the database.

37.  Name a tablespace automatically created when you create a database.

The SYSTEM tablespace.

38.  When creating a user, what permissions must you grant to allow them to connect to the database?

Grant the CONNECT to the user.

39.  How do you add a data file to a tablespace?

ALTER TABLESPACE <tablespace_name> ADD DATAFILE <datafile_name> SIZE <size>

40.  How do you resize a data file?

ALTER DATABASE DATAFILE <datafile_name> RESIZE <new_size>;

41.  What view would you use to look at the size of a data file?

DBA_DATA_FILES

42.  What view would you use to determine free space in a tablespace?

DBA_FREE_SPACE

43.  How would you determine who has added a row to a table?

Turn on fine grain auditing for the table.

44.  How can you rebuild an index?

ALTER INDEX <index_name> REBUILD;

45.  Explain what partitioning is and what its benefit is.

Partitioning is a method of taking large tables and indexes and splitting them into smaller, more manageable pieces.

46.  You have just compiled a PL/SQL package but got errors, how would you view the errors?

SHOW ERRORS

47.  How can you gather statistics on a table?

The ANALYZE command.

48.  How can you enable a trace for a session?

Use the DBMS_SESSION.SET_SQL_TRACE or

Use ALTER SESSION SET SQL_TRACE = TRUE;

49.  What is the difference between the SQL*Loader and IMPORT utilities?

These two Oracle utilities are used for loading data into the database. The difference is that the import utility relies on the data being produced by another Oracle utility EXPORT while the SQL*Loader utility allows data to be loaded that has been produced by other utilities from different data sources just so long as it conforms to ASCII formatted or delimited files.

50.  Name two files used for network connection to a database.

TNSNAMES.ORA and SQLNET.ORA

Technical - UNIX

Every DBA should know something about the operating system that the database will be running on. The questions here are related to UNIX but you should equally be able to answer questions related to common Windows environments.

1.  How do you list the files in an UNIX directory while also showing hidden files?

ls -ltra

2.  How do you execute a UNIX command in the background?

Use the "&"

3.  What UNIX command will control the default file permissions when files are created?

Umask

4.  Explain the read, write, and execute permissions on a UNIX directory.

Read allows you to see and list the directory contents.

Write allows you to create, edit and delete files and subdirectories in the directory.

Execute gives you the previous read/write permissions plus allows you to change into the directory and execute programs or shells from the directory.

5.  the difference between a soft link and a hard link?

A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system.

6.  Give the command to display space usage on the UNIX file system.

df -lk

7.  Explain iostat, vmstat and netstat.

Iostat reports on terminal, disk and tape I/O activity.

Vmstat reports on virtual memory statistics for processes, disk, tape and CPU activity.

Netstat reports on the contents of network data structures.

8.  How would you change all occurrences of a value using VI?

Use :%s/<old>/<new>/g

9.  Give two UNIX kernel parameters that effect an Oracle install

SHMMAX & SHMMNI

10.  Briefly, how do you install Oracle software on UNIX.

Basically, set up disks, kernel parameters, and run orainst.

I hope that these interview questions were not too hard. Remember these are "core" DBA questions and not necessarily related to the Oracle options that you may encounter in some interviews. Take a close look at the requirements for any job and try to extract questions that interviewers may ask from manuals and real life experiences. For instance, if they are looking for a DBA to run their databases in RAC environments, you should try to determine what hardware and software they are using BEFORE you get to the interview. This would allow you to brush up on particular environments and not be caught off-guard. Good luck!

» See All Articles by Columnist James Koopmann



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