Oracle DBA Interview Questions and Answers pdf free download

Below is the list of latest and updated Oracle DBA interview questions and their answers for freshers as well as experienced users. These interview questions will help you to prepare for the interviews, So let's start....
1. What are four common errors found in an alert .log?
2. What is PCT Free/PCT Used/PCT increase parameter in segment? What is growth factor?
3. What is dump destination? What are bdump, cdump and udump?
4. What will you do if in any condition you do not know how to troubleshoot the error at all and there are no seniors or your co-workers around?
5. I am getting error "No Communication channel" after changing the domain name? What is the solution?
6. You have taken import of a table in a database. You have got the Integrity constraint violation error. How you are going to resolve it.
7. What is the most important action a DBA must perform after changing the database from NOARCHIVELOG TO ARCHIVELOG?
8. Show one instance when you encountered an error in alert log and you overcome that error. What actions you took to overcome that error.
9. What is Ora-1555 Snapshot too Old error? Explain in detail?
10. I have applied the following commands: Now what will happen, will the database will give an error / it will work?
11. What is mutated trigger? In single user mode we got mutated error, as a DBA how you will resolve it?
12. Explain Dual table. 
13. As an Oracle DBA what are the entire UNIX file you should be familiar with?
14. What is a Database instance?
15. What are the Requirements of simple Database?
16. Which process writes data from data files to database buffer cache?
17. How to DROP an Oracle Database?
18. How can be determining the size of the log files.
19. What is difference between Logical Standby Database and Physical Standby database?
20. What is full backup?
21. While taking hot backup (begin end backup) what will happens back end?
22. Which is the best option used to move database from one server to another serve on same network and Why?
23. What is Different Type of RMAN Backup?
24. Give one method for transferring a table from one schema to another:
25. What is the purpose of the IMPORT option IGNORE? What is its default setting?
26. What happens when the DEFAULT and TEMP tablespace clauses are left out from CREATE USER statements?
27. What happens if the constraint name is left out of a constraint clause?
28. What happens if a Tablespace clause is left off of a primary key constraint clause?
29. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause?
30. Using hot backup without being in archive log mode, can you recover in the event of a failure? Why or why not?
31. What causes the "snapshot too old" error? How can this be prevented or mitigated?
32. How can you tell if a database object is invalid?
33. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check?
34. A developer is trying to create a view and the database won’t let him. 
35. If you have an example table, what is the best way to get sizing data for the production table implementation?
36. How can you find out how many users are currently logged into the database? How can you find their operating system id?
37. How can you determine if an index needs to be dropped and rebuilt?
38. What is tkprof and how is it used?
39. What is Explain plan and how is it used?
40. How do you prevent output from coming to the screen?
41. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?
42. How do you generate file output from SQL?
43. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.
44. How do you set up tablespaces during an Oracle installation?
45. You see multiple fragments in the SYSTEM tablespace, what should you check first?
46. What are some indications that you need to increase the SHARED_POOL_SIZE parameter?
47. Guideline for sizing db_block_size and db_multi_block_read for an application that does many full table scans?
48. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad -How do you correct it?
49. When should you increase copy latches? What parameters control copy latches?
50. Where can you get a list of all initialization parameters for your instance? How about an indication if they are default settings or have been changed?
51. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning?
52. Discuss row chaining, how does it happen? How can you reduce it? How do you correct it?
53. You are getting busy buffer waits. Is this bad? How can you find what is causing it?
54. If you see contention for library caches how you can fix it?
55. If you see statistics that deal with "undo" what are they really talking about?
56. If a tablespace has a default pctincrease of zero what will this cause (in relationship to the SMON process)?
57. If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only)
58. How can you tell if a tablespace has excessive fragmentation?
59. You see the following on a status report: redo log space requests 23 redo log space wait time 0 Is this something to worry about? What if redo log space wait time is high? How can you fix this?
60. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a problem? If so, how do you fix it?
61. If you see the value for reloads is high in the estat library cache report is this a matter for concern?
62. You look at the dba_rollback_segs view and see that there is a large number of shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is a problem?
63. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem?
64. You see multiple extents in the Temporary Tablespace. Is this a problem?
65. How do you set up your Tablespace on installation Level: Low?
66. You have installed Oracle and you are now setting up the actual instance. You have been waiting an hour for the initialization script to finish, what should you check first to determine if there is a problem?
67. When configuring SQLNET on the server what files must be set up?
68. When configuring SQLNET on the client what files need to be set up?
69. You have just started a new instance with a large SGA on a busy existing server. Performance is terrible, what should you check for?
70. What OS user should be used for the first part of an Oracle installation (on UNIX)?
71. When should the default values for Oracle initialization parameters be used as is?
72. How many control files should you have? Where should they be located?
73. How many redo logs should you have and how should they be configured for maximum recoverability?
74. Why are recursive relationships bad? How do you resolve them?
75. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")?
76. How should a many-to-many relationship be handled?
77. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used?
78. When should you consider de-normalization?
79. How can you determine the space left in a file system?
80. How can you determine the number of SQLNET users logged in to the UNIX system?
81. What command is used to type files to the screen?
82. Can you remove an open file under UNIX?
83. What is the purpose of the grep command?
84. The system has a program that always includes the word nocomp in its name, how can you determine the number of processes that are using this program?
85. The system administrator tells you that the system has not been rebooted in 6 months, should he be proud of this?
86. How can you find dead processes?
87. How can you find all the processes on your system?
88. How can you find your id on a system?
89. What is the finger command?
90. What is the easiest method to create a file on UNIX?
91. What does >> do?
92. If you are not sure what command does a particular UNIX function what is the best way to determine the command?
93. How can you determine if an Oracle instance is up from the operating system level?
94. Users from the PC clients are getting messages indicating : ORA-06114: NETTCP: SID lookup failure. What could the problem be?
95. Users from the PC clients are getting the following error stack:
96. How can you determine if the SQLNET process is running for SQLNET V1? How about V2?
97. What file will give you Oracle instance status information? Where is it located?
98. Users are not being allowed on the system. The following message is received: ORA-00257 archiver is stuck. Connect internal only, until freed. What is the problem?
99. Where would you look to find out if a redo log was corrupted assuming you are using Oracle mirrored redo logs?
100. You attempt to add a datafile and get: ORA-01118: cannot add anymore datafiles: limit of 40 exceeded. What is the problem and how can you fix it?
101. You look at your fragmentation report and see that smon has not coalesced any of you tablespaces, even though you know several have large chunks of contiguous 
102. Your users get the following error: ORA-00055 maximum number of DML locks exceeded? What is the problem and how do you fix it?
103. You get a call from you backup DBA while you are on vacation. He has corrupted all of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE command. What do you do?
104. You have taken a manual backup of a datafile using OS. How RMAN will know about it?
105. How to Uncatalog Backup?
106. How would you find total size of database in OS level