All Oracle-dba-interview-questions

Oracle DBA interview
questions
Oracle Concepts and Architecture
Database Structures
1. What are the components of
physical database structure of Oracle
database?
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.
2. What are the components of logical
database structure of Oracle
database?
There are tablespaces and database's
schema objects.
3. What is a tablespace?
A database is divided into Logical
Storage Unit called tablespaces. A
tablespace is used to grouped related
logical structures together.
4. What is SYSTEM tablespace and
when is it created?
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.
5. Explain the relationship among
database, tablespace and data file.

Each databases logically divided into
one or more tablespaces one or more
data files are explicitly created for each
tablespace.
6. What is schema?
A schema is collection of database
objects of a user.
7. What are Schema Objects?
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.
8. Can objects of the same schema
reside in different tablespaces?
Yes.
9. Can a tablespace hold objects from
different schemes?
Yes.
10. What is Oracle table?
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.
11. What is an Oracle view?
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.)

12. Do a view contain data?
Views do not contain or store data.
13. Can a view based on another view?
Yes.
14. What are the advantages of views?
- Provide an additional level of table
security, by restricting access to a
predetermined set of rows and columns
of a table.
- Hide data complexity.
- Simplify commands for the user.
- Present the data in a different
perspective from that of the base table.
- Store complex queries.
15. What is an Oracle sequence?
A sequence generates a serial list of
unique numbers for numerical columns
of a database's tables.
16. What is a synonym?
A synonym is an alias for a table, view,
sequence or program unit.
17. What are the types of synonyms?
There are two types of synonyms private
and public.
18. What is a private synonym?
Only its owner can access a private
synonym.
19. What is a public synonym?
Any database user can access a public
synonym.

20. What are synonyms used for?
- 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.
21. What is an Oracle index?
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.
22. How are the index updates?
Indexes are automatically maintained
and used by Oracle. Changes to table
data are automatically incorporated into
all relevant indexes.
23. What are clusters?
Clusters are groups of one or more tables
physically stores together to share
common columns and are often used
together.
24. What is cluster key?
The related columns of the tables in a
cluster are called the cluster key.
25. What is index cluster?
A cluster with an index on the cluster
key.
26. What is hash cluster?

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.
27. When can hash cluster used?
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.
28. What is database link?
A database link is a named object that
describes a "path" from one database to
another.
29. What are the types of database
links?
Private database link, public database
link & network database link.
30. What is private database link?
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.
31. What is public database link?
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.

32. What is network database link?
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.
33. What is data block?
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.
34. How to define data block size?
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.
35. What is row chaining?
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.
36. What is an extent?
An extent is a specific number of
contiguous data blocks, obtained in a
single allocation and used to store a
specific type of information.
37. What is a segment?
A segment is a set of extents allocated
for a certain logical structure.

38. What are the different types of
segments?
Data segment, index segment, rollback
segment and temporary segment.
39. What is a data segment?
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.
40. What is an index segment?
Each index has an index segment that
stores all of its data.
41. What is rollback segment?
A database contains one or more
rollback segments to temporarily store
"undo" information.
42. What are the uses of rollback
segment?
To generate read-consistent database
information during database recovery
and to rollback uncommitted
transactions by the users.
43. What is a temporary segment?
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.
44. What is a datafile?

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 tables
and indexes is physically stored in the
data files allocated for a database.
45. What are the characteristics of
data files?
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.
46. What is a redo log?
The set of redo log files for a database is
collectively known as the database redo
log.
47. What is the function of redo log?
The primary function of the redo log is
to record all changes made to data.
48. What is the use of redo log
information?
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.
49. What does a control file contains?
- Database name
- Names and locations of a database's
files and redolog files.
- Time stamp of database creation.
50. What is the use of control file?

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.
Data Base Administration
51. What is a database instance?
Explain.
A database instance (Server) is a set of
memory structure and background
processes that access a set of database
files. The processes can be shared by all
of the users.
The memory structure that is used to
store the most queried data from
database. This helps up to improve
database performance by decreasing the
amount of I/O performed against data
file.
52. What is Parallel Server?
Multiple instances accessing the same
database (only in multi-CPU
environments)
53. What is a schema?
The set of objects owned by user
account is called the schema.
54. What is an index? How it is
implemented in Oracle database?

An index is a database structure used by
the server to have direct access of a row
in a table. An index is automatically
created when a unique of primary key
constraint clause is specified in create
table command
55. What are clusters?
Group of tables physically stored
together because they share common
columns and are often used together is
called cluster.
56. What is a cluster key?
The related columns of the tables are
called the cluster key. The cluster key is
indexed using a cluster index and its
value is stored only once for multiple
tables in the cluster.
57. What are the basic element of base
configuration of an Oracle database?
It consists of
one or more data files.
one or more control files.
two or more redo log files.
The Database contains
multiple users/schemas
one or more rollback segments
one or more tablespaces
Data dictionary tables
User objects (table,indexes,views
etc.,)
The server that access the database
consists of
SGA (Database buffer,
Dictionary Cache Buffers, Redo log
buffers, Shared SQL pool)
SMON (System MONito)
PMON (Process MONitor)
LGWR (LoG Write)
DBWR (Data Base Write)
ARCH (ARCHiver)

CKPT (Check Point)
RECO
Dispatcher
User Process with associated
PGS
58. What is a deadlock? Explain.
Two processes waiting to update the
rows of a table, which are locked by
other processes then deadlock arises.
In a database environment this will often
happen because of not issuing the proper
row lock commands. Poor design of
front-end application may cause this
situation and the performance of server
will reduce drastically.
These locks will be released
automatically when a commit/rollback
operation performed or any one of this
processes being killed externally.
Memory Management
59. What is SGA?
The System Global Area in an Oracle
database is the area in memory to
facilitate the transfer of information
between users. It holds the most recently
requested structural information between
users. It holds the most recently
requested structural information about
the database. The structure is database
buffers, dictionary cache, redo log buffer
and shared pool area.
60. What is a shared pool?

The data dictionary cache is stored in an
area in SGA called the shared pool. This
will allow sharing of parsed SQL
statements among concurrent users.
61. What is mean by Program Global
Area (PGA)?
It is area in memory that is used by a
single Oracle user process.
62. What is a data segment?
Data segment are the physical areas
within a database block in which the
data associated with tables and clusters
are stored.
63. What are the factors causing the
reparsing of SQL statements in SGA?
Due to insufficient shared pool size.
Monitor the ratio of the reloads takes
place while executing SQL statements. If
the ratio is greater than 1 then increase
the SHARED_POOL_SIZE.
Database Logical & Physical
Architecture
64. What is Database Buffers?
Database buffers are cache in the SGA
used to hold the data blocks that are read
from the data segments in the database
such as tables, indexes and clusters
DB_BLOCK_BUFFERS parameter in
INIT.ORA decides the size.
65. What is dictionary cache?

Dictionary cache is information about
the database objects stored in a data
dictionary table.
66. What is meant by recursive hints?
Number of times processes repeatedly
query the dictionary table is called
recursive hints. It is due to the data
dictionary cache is too small. By
increasing the SHARED_POOL_SIZE
parameter we can optimize the size of
data dictionary cache.
67. What is redo log buffer?
Changes made to the records are written
to the on-line redo log files. So that they
can be used in roll forward operations
during database recoveries. Before
writing them into the redo log files, they
will first brought to redo log buffers in
SGA and LGWR will write into files
frequently. LOG_BUFFER parameter
will decide the size.
68. How will you swap objects into a
different table space for an existing
database?
- Export the user
- Perform import using the command
imp system/manager file=export.dmp
indexfile=newrite.sql. This will create all
definitions into newfile.sql.
- Drop necessary objects.
- Run the script newfile.sql after altering
the tablespaces.
- Import from the backup for the
necessary objects.
69. List the Optional Flexible
Architecture (OFA) of Oracle
database? How can we organize the
tablespaces in Oracle database to have
maximum performance?

SYSTEM - Data dictionary tables.
DATA - Standard operational tables.
DATA2- Static tables used for standard
operations
INDEXES - Indexes for Standard
operational tables.
INDEXES1 - Indexes of static tables
used for standard operations.
TOOLS - Tools table.
TOOLS1 - Indexes for tools table.
RBS - Standard Operations Rollback
Segments,
RBS1,RBS2 - Additional/Special
Rollback segments.
TEMP - Temporary purpose tablespace
TEMP_USER - Temporary tablespace
for users.
USERS - User tablespace.
70. How will you force database to use
particular rollback segment?
SET TRANSACTION USE
ROLLBACK SEGMENT rbs_name.
71. What is meant by free extent?
A free extent is a collection of
continuous free blocks in tablespace.
When a segment is dropped its extents
are reallocated and are marked as free.
72.Which parameter in Storage clause
will reduce number of rows per block?
PCTFREE parameter
Row size also reduces no of rows per
block.
73. What is the significance of having
storage clause?
We can plan the storage for a table as
how much initial extents are required,

how much can be extended next, how
much % should leave free for managing
row updating, etc.,
74. How does Space allocation table
place within a block?
Each block contains entries as follows
Fixed block header
Variable block header
Row Header, row date (multiple rows
may exists)
PCTEREE (% of free space for row
updating in future)
75. What is the role of PCTFREE
parameter is storage clause?
This is used to reserve certain amount of
space in a block for expansion of rows.
76. What is the OPTIMAL
parameter?
It is used to set the optimal length of a
rollback segment.
77. What is the functionality of
SYSTEM table space?
To manage the database level
transactions such as modifications of the
data dictionary table that record
information about the free space usage.
78. How will you create multiple
rollback segments in a database?
- Create a database, which implicitly
creates a SYSTEM rollback segment in a
SYSTEM tablespace.
- Create a second rollback segment name
R0 in the SYSTEM tablespace.

- Make new rollback segment available
(after shutdown, modify init.ora file and
start database)
- Create other tablespaces (RBS) for
rollback segments.
- Deactivate rollback segment R0 and
activate the newly created rollback
segments.
79. How the space utilization takes
place within rollback segments?
It will try to fit the transaction in a cyclic
fashion to all existing extents. Once it
found an extent is in use then it forced to
acquire a new extent (number of extents
is based on the optimal size)
80. Why query fails sometimes?
Rollback segment dynamically extent to
handle larger transactions entry loads.
A single transaction may wipeout all
available free space in the rollback
segment tablespace. This prevents other
user using rollback segments.
81. How will you monitor the space
allocation?
By querying DBA_SEGMENT
table/view
82. How will you monitor rollback
segment status?
Querying the DBA_ROLLBACK_SEGS
view
IN USE - Rollback
Segment is on-line.
AVAILABLE - Rollback
Segment available but not on-line.

OFF-LINE - Rollback
Segment off-line
INVALID - Rollback
Segment Dropped.
NEEDS RECOVERY - Contains data
but need recovery or corrupted.
PARTLY AVAILABLE - Contains data
from an unresolved transaction involving
a
distributed
database.
83. List the sequence of events when a
large transaction that exceeds beyond
its optimal value when an entry wraps
and causes the rollback segment to
expand into another extend.
Transaction Begins.
An entry is made in the RES header for
new transactions entry
Transaction acquires blocks in an extent
of RBS
The entry attempts to wrap into second
extent. None is available, so that the
RBS must extent.
The RBS checks to see if it is part of its
OPTIMAL size.
RBS chooses its oldest inactive segment.
Oldest inactive segment is eliminated.
RBS extents
The data dictionary tables for space
management are updated.
Transaction Completes.
84. How can we plan storage for very
large tables?
Limit the number of extents in the table
Separate table from its indexes.
Allocate sufficient temporary storage.

85. How will you estimate the space
required by a non-clustered tables?
Calculate the total header size
Calculate the available data space per
data block
Calculate the combined column lengths
of the average row
Calculate the total average row size.
Calculate the average number rows that
can fit in a block
Calculate the number of blocks and
bytes required for the table.
After arriving the calculation, add 10 %
additional space to calculate the initial
extent size for a working table.
86. It is possible to use raw devices as
data files and what are the advantages
over file system files?
Yes.
The advantages over file system files are
that I/O will be improved because Oracle
is bye-passing the kernel which writing
into disk. Disk corruption will be very
less.
87. What is a Control file?
Database's overall physical architecture
is maintained in a file called control file.
It will be used to maintain internal
consistency and guide recovery
operations. Multiple copies of control
files are advisable.
88. How to implement the multiple
control files for an existing database?
Shutdown the database
Copy one of the existing controlfile to
new location

Edit Config ora file by adding new
control filename
Restart the database.
89. What is redo log file mirroring?
How can be achieved?
Process of having a copy of redo log
files is called mirroring.
This can be achieved by creating group
of log files together, so that LGWR will
automatically writes them to all the
members of the current on-line redo log
group. If any one group fails then
database automatically switch over to
next group. It degrades performance.
90. What is advantage of having disk
shadowing / mirroring?
Shadow set of disks save as a backup in
the event of disk failure. In most
operating systems if any disk failure
occurs it automatically switchover to
place of failed disk.
Improved performance because most OS
support volume shadowing can direct
file I/O request to use the shadow set of
files instead of the main set of files. This
reduces I/O load on the main set of
disks.
91. What is use of rollback segments
in Oracle database?
They allow the database to maintain read
consistency between multiple
transactions.
92. What is a rollback segment entry?
It is the set of before image data blocks
that contain rows that are modified by a
transaction.

Each rollback segment entry must be
completed within one rollback segment.
A single rollback segment can have
multiple rollback segment entries.
93. What is hit ratio?
It is a measure of well the data cache
buffer is handling requests for data.
Hit Ratio = (Logical Reads - Physical
Reads - Hits Misses)/ Logical Reads.
94. When will be a segment released?
When Segment is dropped.
When Shrink (RBS only)
When truncated (TRUNCATE used with
drop storage option)
95. What are disadvantages of having
raw devices?
We should depend on export/import
utility for backup/recovery (fully
reliable)
The tar command cannot be used for
physical file backup, instead we can use
dd command, which is less flexible and
has limited recoveries.
96. List the factors that can affect the
accuracy of the estimations?
- The space used transaction entries and
deleted records, does not become free
immediately after completion due to
delayed cleanout.
- Trailing nulls and length bytes are not
stored.
- Inserts of, updates to and deletes of
rows as well as columns larger than a

single data block, can cause
fragmentation a chained row pieces.
Database Security & Administration
97. What is user Account in Oracle
database?
A user account is not a physical structure
in database but it is having important
relationship to the objects in the database
and will be having certain privileges.
98. How will you enforce security
using stored procedures?
Don't grant user access directly to tables
within the application.
Instead grant the ability to access the
procedures that access the tables.
When procedure executed it will execute
the privilege of procedures owner. Users
cannot access tables except via the
procedure.
99. What are the dictionary tables
used to monitor a database space?
DBA_FREE_SPACE
DBA_SEGMENTS
DBA_DATA_FILES.
SQL*Plus Statements

100. What are the types of SQL
statement?
Data Definition Language: CREATE,
ALTER, DROP, TRUNCATE,
REVOKE, NO AUDIT & COMMIT.
Data Manipulation Language: INSERT,
UPDATE, DELETE, LOCK TABLE,
EXPLAIN PLAN & SELECT.
Transactional Control: COMMIT &
ROLLBACK
Session Control: ALTERSESSION &
SET ROLE
System Control: ALTER SYSTEM.
101. What is a transaction?
Transaction is logical unit between two
commits and commit and rollback.
102. What is difference between
TRUNCATE & DELETE?
TRUNCATE commits after deleting
entire table i.e., cannot be rolled back.
Database triggers do not fire on
TRUNCATE
DELETE allows the filtered deletion.
Deleted records can be rolled back or
committed.
Database triggers fire on DELETE.
103. What is a join? Explain the
different types of joins?
Join is a query, which retrieves related
columns or rows from multiple tables.
Self Join - Joining the table with itself.
Equi Join - Joining two tables by
equating two common columns.
Non-Equi Join - Joining two tables by
equating two common columns.
Outer Join - Joining two tables in such a
way that query can also retrieve rows

that do not have corresponding join
value in the other table.
104. What is the sub-query?
Sub-query is a query whose return
values are used in filtering conditions of
the main query.
105. What is correlated sub-query?
Correlated sub-query is a sub-query,
which has reference to the main query.
106. Explain CONNECT BY PRIOR?
Retrieves rows in hierarchical order eg.
select empno, ename from emp where.
107. Difference between SUBSTR and
INSTR?
INSTR (String1, String2 (n, (m)),
INSTR returns the position of the m-th
occurrence of the string 2 in string1. The
search begins from nth position of
string1.
SUBSTR (String1 n, m)
SUBSTR returns a character string of
size m in string1, starting from n-th
position of string1.
108. Explain UNION, MINUS,
UNION ALL and INTERSECT?
INTERSECT - returns all distinct rows
selected by both queries.
MINUS - returns all distinct rows
selected by the first query but not by the
second.
UNION - returns all distinct rows
selected by either query

UNION ALL - returns all rows
selected by either query, including all
duplicates.
109. What is ROWID?
ROWID is a pseudo column attached to
each row of a table. It is 18 characters
long, blockno, rownumber are the
components of ROWID.
110. What is the fastest way of
accessing a row in a table?
Using ROWID.
CONSTRAINTS
111. What is an integrity constraint?
Integrity constraint is a rule that restricts
values to a column in a table.
112. What is referential integrity
constraint?
Maintaining data integrity through a set
of rules that restrict the values of one or
more columns of the tables based on the
values of primary key or unique key of
the referenced table.
113. What is the usage of
SAVEPOINTS?
SAVEPOINTS are used to subdivide a
transaction into smaller parts. It enables
rolling back part of a transaction.
Maximum of five save points are
allowed.
114. What is ON DELETE
CASCADE?
When ON DELETE CASCADE is
specified Oracle maintains referential
integrity by automatically removing

dependent foreign key values if a
referenced primary or unique key value
is removed.
115. What are the data types allowed
in a table?
CHAR, VARCHAR2, NUMBER,
DATE, RAW, LONG and LONG RAW.
116. What is difference between
CHAR and VARCHAR2? What is the
maximum SIZE allowed for each
type?
CHAR pads blank spaces to the
maximum length.
VARCHAR2 does not pad blank spaces.
For CHAR the maximum length is 255
and 2000 for VARCHAR2.
117. How many LONG columns are
allowed in a table? Is it possible to use
LONG columns in WHERE clause or
ORDER BY?
Only one LONG column is allowed. It is
not possible to use LONG column in
WHERE or ORDER BY clause.
118. What are the pre-requisites to
modify datatype of a column and to
add a column with NOT NULL
constraint?
- To modify the datatype of a column
the column must be empty.
- To add a column with NOT NULL
constrain, the table must be empty.
119. Where the integrity constraints
are stored in data dictionary?
The integrity constraints are stored in
USER_CONSTRAINTS.

120. How will you activate/deactivate
integrity constraints?
The integrity constraints can be enabled
or disabled by ALTER TABLE
ENABLE CONSTRAINT / DISABLE
CONSTRAINT.
121. If unique key constraint on
DATE column is created, will it
validate the rows that are inserted
with SYSDATE?
It won't, Because SYSDATE format
contains time attached with it.
122. What is a database link?
Database link is a named path through
which a remote database can be
accessed.
123. How to access the current value
and next value from a sequence? Is it
possible to access the current value in
a session before accessing next value?
Sequence name CURRVAL, sequence
name NEXTVAL. It is not possible.
Only if you access next value in the
session, current value can be accessed.
124. What is CYCLE/NO CYCLE in a
Sequence?
CYCLE specifies that the sequence
continue to generate values after
reaching either maximum or minimum
value. After pan-ascending sequence
reaches its maximum value, it generates
its minimum value. After a descending
sequence reaches its minimum, it
generates its maximum.
NO CYCLE specifies that the sequence
cannot generate more values after

reaching its maximum or minimum
value.
125. What are the advantages of
VIEW?
- To protect some of the columns of a
table from other users.
- To hide complexity of a query.
- To hide complexity of calculations.
126. Can a view be
updated/inserted/deleted? If Yes -
under what conditions?
A View can be updated/deleted/inserted
if it has only one base table if the view is
based on columns from one or more
tables then insert, update and delete is
not possible.
127. If a view on a single base table is
manipulated will the changes be
reflected on the base table?
If changes are made to the tables and
these tables are the base tables of a view,
then the changes will be reference on the
view.
Oracle Tips & Tricks: Senior Oracle DBA interview questions
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127 Oracle DBA job
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I recently went on an interview for Senior Oracle DBA position. Prior the interview
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Courtesy of our member: tyager
DBA routine
-----------
[1] Here are
some
categories of
parameters for
routine
monitoring.
Can you
suggest any
more? How
would you
monitor each?
Memory
Storage
Disk I/O
Networking
----------
[1] Say an
application
server uses a
pool of 20
database
connections.
They are
shared among
some
hundreds of
concurrent
users, so each
connection is
active most of
the time. The
database is on
another
machine. How
would you use
Multi Threaded
Server in
these
circumstances
[2] What's
going on here?
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Re: Senior Oracle DBA interview questions (Score: 1)
by terranscv (terran@oracle.com) on Jan 27, 2003 - 04:28 AM
(User info | Send a Message) http://
Some quick answers...
TUNING [2] -- use trace files and tkprof
SHELL [1] --
view: $ tar -tvf ./arch1.tar
extract: $ tar -xvf ./arch1.tar
SHELL [3] -- $ egrep "ORA-00054" *log -r
SHELL [4] -- $ ls -la
SOLARIS [1] -- smtx = mutex stall (type of locking), number of times a CPU failed to obtain a
mutex immediately. smtx=0 all is OK (smtx above 500 = big problem)..... impact: [big smtx] =
[harddisk extremely busy]
SOLARIS [2] -- check swap space: $ /usr/sbin/swap -s
SOLARIS [3] -- setting the kernel memory parameters... for Oracle, modify /etc/system, and server
must have 2 GB RAM (more recommended)
by Administrator on Mar 24, 2003 - 02:52 PM
(User info | Send a Message) http://www.dbaclick.com
If you are looking for more Oracle DBA interview questions, make sure to check these articles too:
Oracle DBA interview questions
127 Oracle DBA job interview questions
How to become Oracle DBA - interview tips and preparation
Good luck on your interviews !!!
by Administrator on Apr 21, 2003 - 02:48 PM
(User info | Send a Message) http://www.dbaclick.com
Hi,
Check out this site for all Sample Question Papers of Major Software Companies:
http://freshersworld.com/questions/questions.html
and also for some job interview tips.
by adrian (nospam@yahoo.com) on May 09, 2003 - 10:17 AM
(User info | Send a Message) http://
I passed my interview last week. It was tough and still waiting for the results. Hope I will get the

position soon.
Here are some of the questions they asked me:
1) Schema A has some objects and created one procedure and granted to Schema B. Schema B has
the same objects like schema A. Schema B executed the procedure like inserting some records. In
this case where the data will be stored whether in Schema A or Schema B?
2) What is mutated trigger, is it the problem of locks. In single user mode we got mutated error, as
a DBA how you will resolve it?
3) In exception handling we have some NOT_FOUND and OTHERS. In inner layer we have some
NOT_FOUND and OTHERS. While executing which one whether outer layer or inner layer will check
first?
4) Dual table explain. Is any data internally storing in dual table. Lot of users are accessing select
sysdate from dual and they getting some millisecond differences. If we execute SELECT SYSDATE
FROM EMP; what error will we get. Why?
5) How can you see the source code of the package?
6) You are regularly changing the package body part. How will you create or what will you do before
creating that package?
7) How do you increase the performance of %LIKE operator?
8) Shall we create procedures to fetch more than one record?
9) If the SQL * Plus hangs for a long time, what is the reason?
10) All the users are complaining that their application is hanging. How you will resolve this
situation in OLTP?
11) How to check to memory gap once the SGA is started in Restricted mode?
12) In which situation whether peak time or off peak time you will execute the ANALYZE TABLE
command. Why?
13) If the large table contains thousands of records and the application is accessing 35% of the
table which method to use: index searching or full table scan?
14) What are the differences between database designing and database modeling?
15) What are the differences you have seen while installing Oracle on NT and Unix platform?
16) How to do the scheduled task/jobs in Unix platform?
17) What is bulk SQL?
18) If the entire disk is corrupted how will you and what are the steps to recover the database?
Hope that will be helpful to everyone.
Oracle DBA interview questions

1. What are the
different tablespaces in
database?
2. How to drop the
index?
3. How to drop the
column in a table?
4. How to take the
export and import of
users level?
5. What are the new
parameters in imp?
6. If the application is
running very slow? At
what points you need
to go about the
database in order
to improve the
performance?
7. Specifically on
Application Tuning?
8. What are the
possible backups are
there?
9. How to see the free
spaces information in
sun solaris?

10. How to find the
running processes?
11. How to clone the
database?
12. 12. What is Oracle
database instance?
13. 13. What is Oracle
database?
14. 14. Name all the
background
processes?
15. 15. What are
LGWR, SMON,
PMON, DBWR?
Explain in details?
16. What exactly
happens when a user
issues an UPDATE
statement?
17. What are the
various hit ratios in SGA?
How to monitor?
18. What files form a
database? Explain about
control files?
19. 19. When an
UPDATE statement

is very slow, what
will you do?
20. What privileges are
needed to connect to a
database?
21. 21. How to monitor
rollback segment
contention?
22. 22. When
“SNAPSHOT TOO
OLD” error will
occur?
23. 23. What is the
difference between
logical backup and
physical backup?
24. 24. How to export
Oracle tablespace?
25. 25. What is
DIRECT=Y option
in export?
26. 26. Pipe command
syntax
27. 27. How to take hot
backup?
28. 28. What third party
tools, you used for
sql tuning?

29. 29. What is
TRANSACTION
TABLE in rollback
segment?
30. 30. What is the
simplest way to
collect database
statistics?
31. 31. How to
generate trace file?
tkprof options?
32. What is the
difference between rule
based optimization and
cost based optimization?
32. 32. When will you
use NESTED LOOP
join and SORT
MERGE join?
33. What is the
difference between CHAINED
ROW and MIGRATED ROW?
33. 33. Rollback
segment
contention? How do
you solve?
34. 34. What for
OPTIMAL (rollback
segment) size? And
tell me the syntax

how will you define
it?
35. 35. Describe the
exp utility
parameters and
syntax?
36. 36. Describe the
imp utility
parameters and
syntax?
37. 37. Backup
strategy that you
followed for different
clients?
38. 38. What are the
different export
options?
39. 39. How to use
pipe commands in
UNIX during
export?
40. 40. How to find the
running processes?
41. 41. Have you ever
used any database
monitoring tools?
42. 42. If the
application is
running very slow?
At what points you

need to go about
the database in
order to improve the
performance?
43. 43. How to solve
the contention on
Rollback
segments?
44. 44. What are the
parameters you
need to look at in
output file (tkprof)?
How to identify that
the given SQL
statement is bad by
looking into the
tkprof output file?
How to use pipe
commands in UNIX
during export?
45. 45. Tell me about
your technical
background?
46. 46. What were all
the problems you
have faced?
47. What are the
projects that you have
so far involved?
Depending on whether the Orace DBA is OCP certified. I would start the interview with
thesee questions:

1. What is the difference between the WHERE clause and the HAVING clause on a SQL
statement?
2. What is SQL.BSQ?
3. What is the difference between a static and a dynamic cursor and when would you
choose one over the other?
Then, if they cannot answer these questions, likely I would show them to the door. But if
they passed I would continue with questions reserved for those with real experience on
their resume.
4. Describe the most difficult crash and restore you have ever had to deal with in great
and painful detail.
If none ... out the door again or we continue with:
5. What dba_ and v$ objects should be available to developers and why?
6. Go to the whiteboard and demonstrate your knowledge of ALL ASPECTS of the
Oracle Security Model.
7. Explain the difference between UNDO and ROLLBACK as implemented inOracle 9i
and explain why you would use one rather than the other.
8. Then I would ask about what they would do if they received a half-dozen or so
common error messages including ORA-00600 and ORA-01555
and make sure they understood multiversioning and other basic architecture matters.
9. A series of questions hardware platform related such as, if a Solaris environment, what
is in /etc/system and how does it relate to Oracle.
10. Finally I'd ask how they feel about not having a life and carrying a pager 24 hours a
day.
I have come across with the following Senior Oracle DBA questions. For all Oracle DBAs looking for
job or preparing for job interviews, a good test to check your knowledge.
Hope that is going to be helpful for the community. Enjoy.
To read the complete article, click on the Read more ... link. Your comments or additions are

welcome.
Submitted by our member: shelley
1. How many memory layers are in the shared pool?
1/3 of physical memory, can be 2/4k depending on bit of 32 or 64
2. How do you find out from the RMAN catalog if a particular archive log has been
backed-up?
The database should be in ARCHIVE mode if you are going to use RMAN as backup
method.
3. How can you tell how much space is left on a given file system and how much space
each of the file system's subdirectories take-up?
4. Define the SGA and:
• How you would configure SGA for a mid-sized OLTP environment?
• What is involved in tuning the SGA?
5. What is the cache hit ratio, what impact does it have on performance of an Oracle
database and what is involved in tuning it?
6. Other than making use of the statspack utility, what would you check when you are
monitoring or running a health check on an Oracle 8i or 9i database?
7. How do you tell what your machine name is and what is its IP address?
8. How would you go about verifying the network name that the local_listener is
currently using?
9. You have 4 instances running on the same UNIX box. How can you determine which
shared memory and semaphores are associated with which instance?
10. What view(s) do you use to associate a user's SQLPLUS session with his o/s process?
11. What is the recommended interval at which to run statspack snapshots, and why?
12. What spfile/init.ora file parameter exists to force the CBO to make the execution path
of a given statement use an index, even if the index scan may appear to be calculated as

more costly?
13. Assuming today is Monday, how would you use the DBMS_JOB package to schedule
the execution of a given procedure owned by SCOTT to start Wednesday at 9AM and to
run subsequently every other day at 2AM.
14. How would you edit your CRONTAB to schedule the running of /test/test.sh to run
every other day at 2PM?
15. What do the 9i dbms_standard.sql_txt() and
dbms_standard.sql_text() procedures do?
16. In which dictionary table or view would you look to determine at which time a
snapshot or MVIEW last successfully refreshed?
17. How would you best determine why your MVIEW couldn't FAST REFRESH?
18. How does propagation differ between Advanced Replication and Snapshot
Replication (read-only)?
19. Which dictionary view(s) would you first look at to
understand or get a high-level idea of a given Advanced Replication environment?
20. How would you begin to troubleshoot an ORA-03113 error?
21. Which dictionary tables and/or views would you look at to diagnose a locking issue?
22. An automatic job running via DBMS_JOB has failed. Knowing only that "it's failed",
how do you approach troubleshooting this issue?
23. How would you extract DDL of a table without using a GUI tool?
24. You're getting high "busy buffer waits" - how can you find what's causing it?
25. What query tells you how much space a tablespace named "test" is taking up, and
how much space is remaining?
26. Database is hung. Old and new user connections alike hang on impact. What do you
do? Your SYS SQLPLUS session IS able to connect.
27. Database crashes. Corruption is found scattered among the file system neither of your
doing nor of Oracle's. What database recovery options are available? Database is in
archive log mode.
28. Illustrate how to determine the amount of physical CPUs a Unix Box possesses
(LINUX and/or Solaris).

29. How do you increase the OS limitation for open files (LINUX and/or Solaris)?
30. Provide an example of a shell script which logs into SQLPLUS as SYS, determines
the current date, changes the date format to include minutes & seconds, issues a drop
table command, displays the date again, and finally exits.
31. Explain how you would restore a database using RMAN to Point in Time?
32. How does Oracle guarantee data integrity of data changes?
33. Which environment variables are absolutely critical in order to run the OUI?
34. What SQL query from v$session can you run to show how many sessions are logged
in as a particular user account?
35. Why does Oracle not permit the use of PCTUSED with indexes?
36. What would you use to improve performance on an insert statement that places
millions of rows into that table?
37. What would you do with an "in-doubt" distributed transaction?
38. What are the commands you'd issue to show the explain plan for "select * from dual"?
39. In what script is "snap$" created? In what script is
the "scott/tiger" schema created?
40. If you're unsure in which script a sys or system-owned object is created, but you
know it's in a script from a specific directory, what UNIX command from that directory
structure can you run to find your answer?
41. How would you configure your networking files to connect to a database by the name
of DSS which resides in domain icallinc.com?
42. You create a private database link and upon connection, fails with: ORA-2085:
connects to <fully qualified remote db name>. What is the problem? How would you go
about resolving this error?
43. I have my backup RMAN script called "backup_rman.sh". I am on the target
database. My catalog username/password is rman/rman. My catalog db is called rman.
How would you run this shell script
from the o/s such that it would run as a background process?
44. Explain the concept of the DUAL table.

45. What are the ways tablespaces can be managed and how do they differ?
46. From the database level, how can you tell under which time zone a database is
operating?
47. What's the benefit of "dbms_stats" over "analyze"?
48. Typically, where is the conventional directory structure chosen for Oracle binaries to
reside?
49. You have found corruption in a tablespace that contains static tables that are part of a
database that is in NOARCHIVE log mode. How would you restore the tablespace
without losing new data in the other tablespaces?
50. How do you recover a datafile that has not been physically been backed up since its
creation and has been deleted. Provide syntax example.
51. Draft one mock email requesting your on-technical management grant you downtime
to (provide justification where applicable) complete the following tasks:
(1) Generate statistics on a large table;
(2) Generate an RDA – if you don't know what an RDA is please say so.
(3) Rename datafiles.
The following article provides some of the PL/SQL DBA Interviews questions, asked durinng a
Oracle DBA interviews for contractors at a Bank in Luxembourg.
To read the complete article, click on the Read more ...link. Your comments or additions are
welcome.
Submitted by our member: F. Lange - Certified DBA
PL/SQL
1. What are the advantages and disadvantages, compared to the standard SQL and SQL*Plus?
2. Read the exercise. This block has not any compilation errors, sometimes it can have run time
errors. How can you trap the errors and how can I force to execute the everytimes the line B := 10
; ?

Declare
A number ;
B number ;
begin
--
select Col
into A
from tab
where col2 = 'Constant' ;
--
B := 10 ;
--
...
end ;
3. How to display the loop counter at the screen in a PL/SQL loop?
4. How can I display a LONG column? What are the maximum value, how to bypass then?
5. What is the first information displayed when you connect in sqlplus between
sqlplus scott/tiger@db
and
SQL>
6. If you execute the following commands, why in the same session have I different answer?
select 'count=' || to_char ( count ( 1 ) ) from tab where Col = 1 ;
count=100
select 'count=' || to_char ( count ( 1 ) ) from tab where Col = 2 ;
count=110
select 'count=' || to_char ( count ( 1 ) ) from tab ;
count=99
7. How can I have consistency and what are the locks ?
8. Explain the following term by a sentence
Initrans
pctincrease
ORACLE_SID
9. What are the differences betwen tkprof and explain plan?
10. What is an instance and what is a data base ?

11. When start and end a transaction ?
12. What are the database control command language? Give examples.
13. What is a view what are the problems and the benefits of it?
14. What happens in this example?
Create table a ( a number ) ;
Create view V_A as select * from a ;
Alter table a add ( b number ) ;
Alter table a modify ( a not null ) ;
select * from from V_A ;
15. What is a database link what are the problems and the benefits of it ?
select T1.col1 , T2.col2
from TAB1 T1 , TAB2@link2 T2
where T1.col1 = T2.col1
order by T2.col1 ;
16. Look at the queries, in rules base mode does Oracle use the index in the following case?
select .... from tab1 where colonne * 13.85 > 100000 /* column NUMBER */ ;
select .... from tab1 where colonne not > 10000 /* column NUMBER */ ;
select .... from tab1 where colonne = 123 /* column CHAR */ ;
select .... from tab1 where trunc ( colonne ) = trunc ( sysdate ) /* column date */ ;
select .... from tab1 where rowid = '000001D3.0000.0001' ;
select .... from tab1 where substr ( colonne , 1 , 5 ) = 'MAIN:' /* column CHAR */ ;
select .... from tab1 where colonne not in ( select colonne from tab1 where col2 = 123 ) ; /* col2
number */ ;
DBA
1. Explain by one sentences, role, references, privilege on a table and profile?
2. What can trigger a snapshot to old error?
3. What are the DB files, how oracle discover them?
4. Where do you look for the trace file?
5. The following question about implementation. The answer is not a number but the way you do it.
You have got a raw partition. The size is 800M
dd if=/dev/rdsk/c.t.d.s. of=/dev/null bs=1024
819200 block.
You create one file table space what is it's maximum size available for the rollback and what is the
maximum size for rollback? Explain how the extents for rollback segments are allocated?
9. How to backup a database and made a recovery of a table?

10. How do you chose your db_block_size ?
11. A database has been created with the default parameters how do you increase the
DB_BLOCK_SIZE and the DB_FILE?
12. How can you move the tablespace ROLLBACK from one disk to an other, given this information?
select segment_name , tablespace_name , status , owner from
dba_rollback_segs ;
SYSTEM SYSTEM ONLINE SYS
RBS1 ROLLBACK ONLINE PUBLIC
RBS2 ROLLBACK ONLINE PUBLIC
select tablespace_name , file_name from dba_data_files where
tablespace_name = 'ROLLBACK' ;
ROLLBACK /dev/rdsk/c0t0d0s0
New location is /dev/rdsk/c1t1d0s0
13. Estimate the size of the table? The answer is not a number but a list of steps you will use to
derive this number.
create table emp ( emp_id number not null ,
name varchar2(50) not null ,
surname varchar2(50) not null,
social_number varchar2(10) ) ;
emp will contains 1000 static rows.
14. Same question but the table already exists and has one extents of 1Gbytes ?
15. How to shutdown a database in Oracle version 8i and 9i?
PRO*C
1. When you can NOT use Pro*C ? Where in your application you can use Embedded SQL?
2. Explain:
ORACA
SQLCA
SQLDA
ora-1403 OR ora-100
3. What will happen in this example?
EXEC SQL AT DB1 DECLARE CURSOR C1 AS SELECT COL1 FROM TABLE2 WHERE COL =
:VAR1 ;
EXEC SQL AT DB1 OPEN C1 ;
EXEC SQL AT DB1 FETCH C1 INTO :VAR2 ;
while ( .... )
{
EXEC SQL AT DB1 UPADTE TABLE1 SET COL1 = COL1 WHERE COL2 = :VAR ;
if ( ......)
{

}
EXEC SQL AT DB2 UPDATE TABLE1 SET COL1 = COL1 + 1 WHERE COL2 = :VAR ;
if ( ....)
{
}
EXEC SQL AT DB1 COMMIT ;
EXEC SQL AT DB2 COMMIT ;
EXEC SQL AT DB1 FETCH C1 INTO :VAR2 ;
}
EXEC SQL AT DB1 CLOSE C1 ;
...
4. How can you know a value fetch is null ?
OCI
1. Explain the following?
lda
hda
2. Translate the following logical model to a physical one (tables,indexes,constraints ... )? Explain
how do you read the relation between these two entities.
A (a1 a2 a3 a4 ... an) 1,1 <-> 0,N B (b1 b2 b3 ... bm)
A (a1 a2 a3 a4 ... an) 1,1 <-> 0,1 B (b1 b2 b3 ... bm)
A (a1 a2 a3 a4 ... an) 1,1 <-> 1,N B (b1 b2 b3 ... bm)
A (a1 a2 a3 a4 ... an) 1,1 <-> 1,1 B (b1 b2 b3 ... bm)
I just wanted to share with all DBA's looking for new job opportunities some of the Oracle DBA
interviews questions a fiend of mine had when attending one job interview.
Hope that would help you better prepare for your interviews and know what type of questions are
usually asked.
To read the complete article, click on the Read more ... link. Your comments or additions are
welcome.
Submitted by our member: The Guru
1. Three users at a time giving the following command:

alter database backup controlfile to trace;
How can you differentiate the file using the filename itself?
2. When you execute:
alter tablespace begin backup;
How can Oracle engine can identify that the corresponding datafiles are in backupmode?
3. When exporting using filesize parameter I have generated three files. How the oracle
name this three files?
4. One of my rollback segments got corrupted? How can I rectified?
5. When yesterday developer gives the following command:
select count(*) from
it gives the output within minutes
Today the same command takes hours? What will u check?
6. When the developer trying to compile the package. But the database gets hanged?
What will u check?
7. What is the use of query in Tkprof?
8. What is the maximum number of value allowed in parse column?
9. How can we force the query not to use the index? (Something else then a using a hint)
10. Till yesterday the query is running smoothly. But today the develper is complaining?
How will u start your tuning?
11. What is the difference between count(*) and count(1)?
12. As a Oracle DBA what are all the UNIX file you should be familar with?

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