Most Frequently Oracle Core Dba Interview Questions and Answers
1. Question 1. What Is Consistent
Backup?
Answer :
A Consistent backup is one in
which the files being backed up contain all changes upto the same system change
number (SCN).
2. Question 2. What Is Fractured
Block?
Answer :
Because the database continues
writing to the file during an online backup, there is the possibility of
backing up inconsistent data within a block. For example, assume that either
RMAN or an operating system utility reads the block while database writer is in
the middle of updating the block. In this case, RMAN or the copy utility could
read the old data in the top half of the block and the new data in the bottom
top half of the block. The block is a fractured block, meaning that the data in
this block is not consistent.
3. Question 3. What Are The Steps
To Performing Complete Recovery On The Whole Database?
Answer :
o
Mount the database
o
Ensure that all
datafiles you want to recover are online
o
Restore a backup
of the whole database or the files you want to recover
o
Apply online or
archived redo logs, or a combination of the two
4. Question 4. What Are The Steps
To Performing Complete Recovery On A Tablespace Or Datafile?
Answer :
o
Take the
tablespace or datafile to be recovered offline if the database is open.
o
Restore a backup
of the datafiles you want to recover.
o
Apply online or
archived redo logs, or a combination of the two.
5. Question 5. What Are The
Components Of Physical Database Structure Of Oracle Database?
Answer :
Oracle database is comprised
of three types of files. One or more datafiles, two are more redo log files,
and one or more control files.
6. Question 6. What Are The
Components Of Logical Database Structure Of Oracle Database?
Answer :
There are tablespaces and
database's schema objects.
7. Question 7. What Is A
Tablespace?
Answer :
A database is divided into
Logical Storage Unit called tablespaces. A tablespace is used to grouped
related logical structures together.
8. Question 8. What Is System
Tablespace And When Is It Created?
Answer :
Every Oracle database contains
a tablespace named SYSTEM, which is automatically created when the database is
created. The SYSTEM tablespace always contains the data dictionary tables for
the entire database.
9. Question 9. Explain The
Relationship Among Database, Tablespace And Data File?
Answer :
Each databases logically
divided into one or more tablespaces one or more data files are explicitly
created for each tablespace.
10. Question 10. What Is Schema?
Answer :
A schema is collection of
database objects of a user.
11. Question 11. What Are Schema
Objects?
Answer :
Schema objects are the logical
structures that directly refer to the database's data. Schema objects include
tables, views, sequences, synonyms, indexes, clusters, database triggers,
procedures, functions packages and database links.
12. Question 12. Can Objects Of
The Same Schema Reside In Different Tablespaces?
Answer :
Yes.
13. Question 13. Can A Tablespace
Hold Objects From Different Schemes?
Answer :
Yes
14. Question 14. What Is Oracle
Table?
Answer :
A table is the basic unit of
data storage in an Oracle database. The tables of a database hold all of the
user accessible data. Table data is stored in rows and columns.
15. Question 15. What Is An Oracle
View?
Answer :
A view is a virtual table.
Every view has a query attached to it. (The query is a SELECT statement that
identifies the columns and rows of the table(s) the view uses.)
16. Question 16. Do A View Contain
Data?
Answer :
Views do not contain or store
data.
17. Question 17. Can A View Based
On Another View?
Answer :
Yes.
18. Question 18. What Are The
Advantages Of Views?
Answer :
o
Provide an
additional level of table security, by restricting access to a predetermined
set of rows and columns of a table.
o
Hide data
complexity.
o
Simplify commands
for the user.
o
Present the data
in a different perspective from that of the base table.
o
Store complex
queries.
19. Question 19. What Is An Oracle
Sequence?
Answer :
A sequence generates a serial
list of unique numbers for numerical columns of a database's tables.
20. Question 20. What Is A
Synonym?
Answer :
A synonym is an alias for a
table, view, sequence or program unit.
21. Question 21. What Are The
Types Of Synonyms?
Answer :
There are two types of
synonyms private and public.
22. Question 22. What Is A Private
Synonym?
Answer :
Only its owner can access a
private synonym.
23. Question 23. What Are Synonyms
Used For?
Answer :
Mask the real name and owner
of an object. - Provide public access to an object - Provide location
transparency for tables, views or program units of a remote database. -
Simplify the SQL statements for database users.
24. Question 24. What Is An Oracle
Index?
Answer :
An index is an optional
structure associated with a table to have direct access to rows, which can be
created to increase the performance of data retrieval. Index can be created on
one or more columns of a table.
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25. Question 25. How Are The Index
Updated?
Answer :
Indexes are automatically
maintained and used by Oracle. Changes to table data are automatically
incorporated into all relevant indexes.
26. Question 26. What Are
Clusters?
Answer :
Clusters are groups of one or
more tables physically stores together to share common columns and are often
used together.
27. Question 27. What Is Cluster
Key?
Answer :
The related columns of the
tables in a cluster are called the cluster key.
28. Question 28. What Is Index
Cluster?
Answer :
A cluster with an index on the
cluster key.
29. Question 29. What Is Hash
Cluster?
Answer :
A row is stored in a hash
cluster based on the result of applying a hash function to the row's cluster
key value. All rows with the same hash key value are stores together on disk.
30. Question 30. When Can Hash
Cluster Used?
Answer :
Hash clusters are better choice
when a table is often queried with equality queries. For such queries the
specified cluster key value is hashed. The resulting hash key value points
directly to the area on disk that stores the specified rows.
31. Question 31. What Is Database
Link?
Answer :
A database link is a named
object that describes a "path" from one database to another.
32. Question 32. What Are The
Types Of Database Links?
Answer :
Private database link, public
database link & network database link.
33. Question 33. What Is Private
Database Link?
Answer :
Private database link is
created on behalf of a specific user. A private database link can be used only
when the owner of the link specifies a global object name in a SQL statement or
in the definition of the owner's views or procedures.
34. Question 34. What Is Public
Database Link?
Answer :
Public database link is
created for the special user group PUBLIC. A public database link can be used
when any user in the associated database specifies a global object name in a
SQL statement or object definition.
35. Question 35. What Is Network
Database Link?
Answer :
Network database link is
created and managed by a network domain service. A network database link can be
used when any user of any database in the network specifies a global object
name in a SQL statement or object definition.
36. Question 36. What Is Data Block?
Answer :
Oracle database's data is
stored in data blocks. One data block corresponds to a specific number of bytes
of physical database space on disk.
37. Question 37. How To Define
Data Block Size?
Answer :
A data block size is specified
for each Oracle database when the database is created. A database users and
allocated free database space in Oracle data blocks. Block size is specified in
init.ora file and cannot be changed latter.
38. Question 38. What Is Row
Chaining?
Answer :
In circumstances, all of the data
for a row in a table may not be able to fit in the same data block. When this
occurs, the data for the row is stored in a chain of data block (one or more)
reserved for that segment.
39. Question 39. What Is An
Extent?
Answer :
An extent is a specific number
of contiguous data blocks, obtained in a single allocation and used to store a
specific type of information.
40. Question 40. What Is A
Segment?
Answer :
A segment is a set of extents
allocated for a certain logical structure.
41. Question 41. What Are The Different
Types Of Segments?
Answer :
Data segment, index segment,
rollback segment and temporary segment.
42. Question 42. What Is A Data
Segment?
Answer :
Each non-clustered table has a
data segment. All of the table's data is stored in the extents of its data
segment. Each cluster has a data segment. The data of every table in the
cluster is stored in the cluster's data segment.
43. Question 43. What Is An Index
Segment?
Answer :
Each index has an index
segment that stores all of its data.
44. Question 44. What Is Rollback
Segment?
Answer :
A database contains one or
more rollback segments to temporarily store "undo" information.
45. Question 45. What Are The Uses
Of Rollback Segment?
Answer :
To generate read-consistent
database information during database recovery and to rollback uncommitted
transactions by the users.
46. Question 46. What Is A
Temporary Segment?
Answer :
Temporary segments are created
by Oracle when a SQL statement needs a temporary work area to complete
execution. When the statement finishes execution, the temporary segment extents
are released to the system for future use.
47. Question 47. What Is A
Datafile?
Answer :
Every Oracle database has one
or more physical data files. A database's data files contain all the database
data. The data of logical database structures such as tablesand indexes is
physically stored in the data files allocated for a database.
48. Question 48. What Are The
Characteristics Of Data Files?
Answer :
A data file can be associated
with only one database. Once created a data file can't change size. One or more
data files form a logical unit of database storage called a tablespace.
49. Question 49. What Is A Redo
Log?
Answer :
The set of redo log files for
a database is collectively known as the database redo log.
50. Question 50. What Is The
Function Of Redo Log?
Answer :
The primary function of the
redo log is to record all changes made to data.
51. Question 51. What Is The Use
Of Redo Log Information?
Answer :
The information in a redo log
file is used only to recover the database from a system or media failure
prevents database data from being written to a database's data files.
52. Question 52. What Does A
Control File Contains?
Answer :
Database name - Names and
locations of a database's files and redolog files. - Time stamp of database
creation.
53. Question 53. What Is The Use
Of Control File?
Answer :
When an instance of an Oracle
database is started, its control file is used to identify the database and redo
log files that must be opened for database operation to proceed. It is also
used in database recovery.
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