ORACLE BASICS INTERVIEW QUESTIONS

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					ORACLE BASICS INTERVIEW QUESTIONS

1. What is difference between varchar and varchar2?

   Varchar means fixed length char             varchar2 means variable length char

2. Difference between oracle8i and oracle9i?

a. The biggest difference between Oracle8i and Oracle9i is that Oracle9i lets you
resize the SGA memory areas dynamically i.e., the Database           Buffer Cache
DB_CACHE_SIZE or the SHARED_POOL_SIZE, etc., can be resized when the database
is up and running. The same is not     possible with Oracle8i. You can get more
information from OTN

b. Oracle 9i is an enhanced version of the Oracle 8i.Oracle 8i does not      provided
time stamping facility, which is provided in Oracle 9i.

c. you can drop a column in oracle 9i using alter table command where as       this is
not available in oracle 8i

d. Database performance ease of management scalability security availability
Windows 2000 integration and application areas: Internet content        management
commerce integration packaged applications Business             Intelligence native
compilation of PL/SQL reduction in latch          contention (SGA locks) and I/O
improvements better Java performance        (better compilation, improved garbage
collection) distributed database      performance enhancements enhanced 3-tier
security (integration with     LDAP...) improved hosting security (through use of
virtual private databases), fine-grained auditing and single sign-on improved user
security (more password management features, etc.)Ability to encrypt stored data
row-level access control (Oracle Label Security)

e. Listed below are some of the features of 9i:
       1) U has automatic undo management.
       2) U has automatic segment space management
       3) U got these locally managed tablespaces which is better than the
       dictionary managed        tablespaces as u can avoid fragmentation with locally
       managed tablespaces.
       4) U has a new dbms_metadata package to extract object definitions from
       database.
       5) Multi table insert is possible with 9i
       6) Importantly u has this spfile in 9i.
       7) Also u has dynamic memory management facility with 9i.
       8) U has tuning advisories with 9i.
       9) U has multi block size parameter with 9i and many more features like
       these.



3.What is Pro*C? What is OCI?
Pro *C
The Pro* c/C++ precompiler takes the SQL statement that embedded in C/C++ code
convert into standard C/C++ code. When successfully precompile this code, the
result is a C or C++ program that we compile and used to build the application that
access the Oracle Application.

OCI: - OCI refer to Oracle Call interface is set of Low Level API (Application Program
Interface Call) used to interact with Oracle Database. By OCI one can use the
operation such as Logon, Fatch, parse, execute etc. Generally these are written in
C/C++.

4. What is the difference between "NULL in C" and "NULL in Oracle?

The NULL in C treated as Zero or void. But in SQL NULL value is Non or blank
represented it can't manipulated

5. In Oracle varchar2 takes dynamic space for storage then why char is still in
oracle?

The major difference between varchar2 and char is fixed length and variable length.
Varchar2 have variable length mean if we declare as 20 space and its use only 5
space the memory assign only 5. But in char takes declare space while use any
number space less than declare

6. What are the difference between and constraints and triggers?

Constraints are used to maintain the integrity and atomicity of database .in other
words it can be said they are used to prevent invalid data entry. The main 5
constraints are
NOT NULL, PRIMARY KEY, FOREIGN KEY, UNIQUE KEY and CHECK

Triggers are basically stored procedures, which automatically fired when any insert,
update or delete is issued on table

Another most imp, Diff. is that trigger affected only those row after which trigger
applied but constraint affected all row of table.

7. What is normalization? What is the advantage of normalization (briefly?)

1. The process of separating data into distinct, unique sets is called normalization.
This is implemented to improve the performance of the RDBMS, such as reduces
redundancy of data and data inconsistency.

2. Normalization is the process of removing redundant data from your tables in
order to improve storage efficiency, data integrity and scalability.

3. Database normalization is a series of steps followed to obtain a database design
that allows for consistent storage and efficient access of data in a relational
database. These steps reduce data redundancy and the risk of data becoming
inconsistent.
4. Normalization is the process used to reduce the unnecessary repetition of data
i.e., redundant data. It is performed on the data, which is redundant and makes the
data in a normalized format. It is of step-by-step process IstNotmal,
FormIIndNormal, formIIIrdNormal, formIVthNormal form or Boyce odd Normal form
By performing this we will get the data in the Normalized formati.,e from DBMS to
RDBMS.

8. How the logs are escalated?

There are different types are logs which are logged by Oracle Database Engine. A
DBA has to look in for alter log which exist background dump dust. The seviourity of
the problem are analysed and escalated based on the information provided by the
alter log.

9.What is structure of Database?

1.Oracle database usually contains one database and a single instance. But, Oracle
9i, 10g RAC (Real Application Clusters) can have multiple instances to interact with
a single database for high availability.
Instance is non-persistent, memory based background processes and structures.
Database is persistent, disk based, data and control files

2.Physical Structure of Database:
One or more data files, control file(s), Redo log file(s) and init.ora file
Logical Structure of Database:
Table spaces, segments, extents, blocks

10.what is the difference between primary key, unique key, and surrogate key?

Primary Key: A column in a table whose values uniquely identify the rows in the
table. A primary key value cannot be NULL.

Unique Key: Unique Keys are used to uniquely identify each row in an Oracle table.
There can be one and only one row for each unique key value.

Surrogate Key: A system generated key with no business value. Usually implemented
with database-generated sequences.

Primary Key                               Unique key
1.There is only one                       1. There may be more than 1
   Primary key for I table                   Unique Key in table

2.It can contain Null Value               2. It can contain Null Value

1. what are the diffrent file types that are supported by SQL*Loader?

       a.direct method (skips dbcache, no redo generation)

       b. conventional method (just opposite of direct load)
2.How to find how many database reside in Oracle server in query?

      select count(*) from v$database;

3.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?

      CBO (Cost Based Optimizer): Generates an execution plan for a SQL
      statement Optimizer_index_cost_adj parameter can be set to help CBO to
      decide an execution plan, which affects the speed of SQL query. We can also
      make necessary changes to the following parameters to effect CBO
      performance:
      Optimizer_search_limit & optimizer_max_permutations

4.How many memory layers are in the shared pool?

      The shared pool portion of the SGA contains three major areas: library cache,
      dictionary cache, buffers for parallel execution messages, and control
      structures.

5.What are the attributes of the Virtual Indexes?

      a. These are permanent and continue to exist unless we drop them.

      b. Their creation will not affect existing and new sessions. Only sessions
         marked for Virtual Index usage will become aware of their existence.

      c. Such indexes will be used only when              the   hidden   parameter
         "_use_nosegment_indexes" is set to true.

      d. The Rule based optimizer did not recognize Virtual Indexes when I
      Tested, however, CBO recognizes them. In all of my examples, I have used
      CBO. However, I did not carry out intensive testing in RBO and you may come
      across exceptions to this view.

      d. Dictionary view DBA_SEGMENTS will not show an entry for Virtual Indexes.
         The table DBA_INDEXES and DBA_OBJECTS will have an entry for them in
         Oracle 8i; in Oracle 9i onwards, DBA_INDEXES no longer show Virtual
         Indexes.

      e. Virtual Indexes cannot be altered and throw a "fake index" error!
      f. Virtual Indexes can be analyzed, using the ANALYZE command or
      DBMS_STATS package, but the statistics cannot be viewed (in Oracle 8i,
      DBA_INDEXES will not show this either). Oracle may be generating artificial
      statistics and storing it somewhere for referring it later.
      Creating Virtual Index
      Creating a Virtual Index can be achieved by using the NOSEGMENT        clause
      with the CREATE INDEX command.


6.What is meant by Virtual Indexes in Oracle?

      Virtual Indexes are another undocumented feature used by Oracle. Virtual
      indexes, as the name suggests are pseudo-indexes that will not behave the
      same way that normal indexes behave, and are meant for a very specific
      purpose. A virtual index is created in a slightly different manner than the
      normal indexes. A virtual index has no segment pegged to it, i.e., the
      DBA_SEGMENTS view will not show an entry for this.

      Oracle handles such indexes internally and few required dictionary tables are
      updated so that the optimizer can be made aware of its presence and
      generate an execution plan considering such indexes.As per Oracle, this
      functionality is not intended for standalone usage. It is part of the Oracle
      Enterprise Manger Tuning Pack (Virtual Index Wizard).

      The virtual index wizard functionality allows the user to test a potential new
      index prior to actually building the new index in the database.It allows the
      CBO to evaluate the potential new index for a selected SQL statement by
      building an explain plan that is aware of the potential new index.

      This allows the user to determine if the optimizer would use the index, once
      implemented.


7.What are materialized views? When are they used?

      Materialized view is like a view but stores both definition of a view plus the
      rows resulting from execution of the view. It uses a query as the bases and
      the query is executated at the time the view is created and the results are
      stored in a table. You can define the Materialized view with the same storage
      parametes as any other table and place it in any tablespace of your choice.
      You can also index and partition the Materialized view table like other tables
      to improve performance of queries executed aginst them.

      Use of Meterialized view:-

     Expensive operations such as joins and aggregations do not need to be re
     executed.
     If the query is astisfied with data in a Meterialized view, the server
     transforms the query to reference the view rather than the base tables.
8.What is a functional index - explain?

      Function-based indexes can use any Function or Object method that is
      declared as repeatable.
      Queries using expressions can use the index.
      Ex: - CREATE INDEX sales_margin_inx
      ON sales (revenue - cost);

      Sql> SELECT ordid
      FROM sales
      WHERE (revenue - cost) > 1000;
      We have to enable Function-based indexes by enableing the following
      initialization parameters
      ALTER SESSION SET QUERY_REWRITE_ENABLED = TRUE;
      ALTER SESSION SET QUERY_REWRITE_INTEGRITY = TRUSTED;

9.Where we use bitmap index?

      a. Bitmap indexes are most appropriate for columns having low distinct
      values.
      b. We can use bitmap index where cardinality is very low like gender column
      or color column.

10.What is an extent?
     a. An extent is the smallest unit of storage allocation comprising collection of
     Blocks.
     b. Well an extent is a chunk of a space that is used by database segments
     when a segment is created it allocates extents.

11.How to you move from dedicated server Process to a Shared Server Process

      Use DBCA (DATABASE CONFIGUARATION ASSISTANT) toolYou will get the
      option to select shared server mode.

12.What are the components of physical database structure of Oracle database?

      A. Totally there are 6 files (components) of physical database structure.3
      mandatory & 3 optional. Three mandatory files are
            1> data file: store actual data
            2> control file: stores structural & status information of database.
            3> redo log file: stores changed/committed data
      Three optional files are
            4>-parameter file: stores all size related parameters note: this file is
            mandatory for a1st time u create a database, and then it is optional.
            5> archive log file: its offline copy of redo log files
            6>-password file: used to make normal user to behave as a super user.

             b.     1. Control files
                    2. Init file
                    3. Log files 4. Redo/archive log files 5. data files
C. Physical components of oracle database are control files, redo log files and
   datafiles.
    Control file: control file is read in the mount state of database. Control file is a
    small binary file, which records the physical structure of database, which
    includes
     Database name
    Names and locations of datafiles and online redo log files. Timestamp of
    database creation
    Checkpoint information current logs sequence number.
    Redo log files: This files saves all the changes that are made to the database
    as they occur. This plays a great role in the database recovery.
    Datafiles: datafiles are the physical files, which stores data of all logical
                structure.

11.What are the components of logical database structure of Oracle database

      Tablespace, segments, extents, data Blocks.

      A logical unit of storage of database is called Tablespace.

      A segment is a space allocated for a specific logical storage structure within a
      tablespace.

      Extents: Space allocated to a segments.

      Datablocks: Oracle server manage the storage space in the datafiles in units is
      called data blocks or oracle blocks.


12.What are the different types of segments?

      table segment, index segment, IOT, cluster, temp segment, data segment.

13.Can you name few DBMS packages and their use?

      DBMS_OUTPUT.PUT_LINE ('strings');
      Print out the strings
      DBMS_UTILITY.get_time ()
      get the current time
       DBMS_ALERT
      e.g    begin
             dbms_alert.register('myregister');
             end
                            To register interst in a named alert

14.How can be determine the size of the log files.
      Select sum (bytes)/1024/1024 size_in_mb from v$log;

15.How can be determine the size of the database?

      A. Select sum (bytes)/1024/1024/1024 Size_in_GB from dba_data_files;

      B. Select sum (bytes)/1024/1024 from v_$datafile + select sum
      (bytes)/1024/1024 from v_$logfile will give u the total size of the database
      C. Select (select sum (bytes/1024/1024/1024) from v$datafile) +( select
      sum(bytes/1024/1024/1024)      from        v$tempfile)       +      (select
      sum(bytes/1024/1024/1024) from v$log) "Size of Database in GB" from dual.

16. How can you check which user has which Role.

      desc dba_tab_privs (OR) Can use ROLE_TAB_PRIVS also (OR) select * from
      dba_role_privs order by grantee;

17. Can you start a database without SPfile in oracle 9i?

      While starting database Oracle reads spfiledb.ora, spfile.ora, initdb.ora or
      init.ora file. Yes it is possible to start the database using init.ora file only.
      The main advantage of using the SPFILE.ora is only to make changes to the
      dynamic initialization parameters without restarting the database using the
      SCOPE option. The changes will be stored in the spfile only and if you start
      the database using "pfile" option those changes wont be applicable to the
      database.

18.Do a view contain data?

      A view does not contain any data of its own, but is like a window through
      which data from other tables can be viewed and changed
      The answer depends on the type of view. In case of normal view, the ans is
      NO it only contains query based on a base table but in case of materialized
      view, YES it does contain data and for the updated data in the base table, it
      needs to be refreshed.

      NO: Because view is for view one or more tables data like query.

19.What is Oracle table?

      A table is the most commonly used form of storing user data.
      A table is used to store the information in form of rows &columns in the
      database.
      Table is a segment (type of Segments), which is used to store user data.
      Tables can have partitions (value wise, date period wise) and each partition
      can have separate tablespace for better performance. The Collection of
      informations stored in the structured format that is called a table.



20.Can objects of the same schema reside in different tablespaces?

      Yes, it can. For example if you specify a different tablepace (B) for indexes,
      the indexes of the tables that the user create would be residing in B, and the
      table would reside in the user's default tablespace A.

      Yes: Schema objects can stored in different tablespace and a tablespace can
      contained one or more schema objects data.
21.What is an Oracle index?

      An Index is a tree structure that allows direct access to a row in a table.
      Indexes can be classified based on their logical design or on their physical
      implementation.
      The Logical classification groups indexes from an application perspective,
      while the physical classification is derived from the way the indexes are
      stored

      An index is a schema object that can speed up the retrieval of rows by using
      pointers. If you do not have an index, then a full table scan occurs. Its
      purpose is to reduce disk I/O by using an indexed path to locate data quickly.
      If a table is dropped, the corresponding indexes are also dropped.

      It is created in existing table to locate rows more quickly&efficiently. The
      users cannot see the indexes; they are just used to speed up the queries


22.Can we create index on long raw column?

      NO we can't create index on long raw column.

23.What is 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/schema's
      - One or more rollback segments
      - One or more tablespaces
      - Data dictionary tables.
      User objects (table, indexes, views etc.)

24.What are clusters?

      Groups of tables physically stored together because they share common
      columns and are often used together is called clusters.

25.What is the function of redo log?

      The primary function of the redo log is to record all changes made to data.

26.What are the characteristics of data files?

      Characterstics of Data File:
      - A Data file can be associated with only one database.
      - Once created, a data file cannot change is size.
      - One or more data files form a logical unit of database storage called a
      Tablespace.
      Datafile size can be change by using ALTER DATABASE .................RESIZE
      command.




ORACLE DBA INTERVIEW QUESTIONS

1.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 segments extents are released to the system for future
use.

2.What are the uses of rollback segment

The use of RollBack Segment is Database is - to maintain read consistency between
multiple transactions.

3.What process writes from data files to buffer cache?
Server Process (OR) it is an server process not DBWR(DataBase Writer)

4.What is a redo log?

Redo log contains the before and after image copies of changed data.

5.What is a on-line redo log?

The On-line Redo Log is a set of tow or more on-line redo files that record all
committed changes made to the database. Whenever a transaction is committed,
the corresponding redo entries temporarily stores in redo log buffers of the SGA
are written to an on-line redo log file by the background process LGWR. The
on-line redo log files are used in cyclical fashion..

6.What does LGWR do ?

It is one of the main background process in oracle . In oracle and unix environment
you can check this process using ps -ef |pg command . which is writting all the
uncommited transaction from SGA to redologfile . (or)
Log Writer (LGWR) writes redo log entries generated in the redo log buffer of the
SGA to on-line Redo Log File.


7.Name init.ora parameters which effects system performance.

These are the Parameters for init.ora

DB_BLOCK_BUFFERS
SHARED_POOL_SIZE
SORT_AREA_SIZE
DBWR_IO_SLAVES
ROLLBACK_SEGMENTS
SORT_AREA_RETAINED_SIZE
DB_BLOCK_LRU_EXTENDED_STATISTICS
SHARED_POOL_RESERVE_SIZE

8.What is a database instance and Explain

An Oracle instance is a combination of background processes and memory structures
(SGA).



9.What are the Advantages of Using DBCA

These are a few of the advantages of using DBCA:

You can use its wizards to guide you through a selection of options providing an easy
means of creating and tailoring your database. It allows you to provide varying
levels of detail. You can provide a minimum of input and allow Oracle to make
decisions for you, eliminating the need to spend time deciding how best to set
parameters or structure the database. Optionally, it allows you to be very specific
about parameter settings and file allocations.

It builds efficient and effective databases that take advantage of Oracle's new
features.

It uses Optimal Flexible Architecture (OFA), whereby database files and
administrative files, including initialization files, follow standard naming and
placement practices


10.How do you find whether the instance was started with pfile or spfile

There are 3 different ways :-

1) SELECT name, value FROM v$parameter WHERE name = 'spfile'; //This query will
return NULL if you are using PFILE

2) SHOW PARAMETER spfile // This query will returns NULL in the value column if
you are using pfile and not spfile

3) SELECT COUNT(*) FROM v$spparameter WHERE value IS NOT NULL; // if the count
is non-zero then the instance is using a spfile, and if the count is zero then it is
using a pfile:
By Default oracle will look into the default location depends on the o/s. Like in
unix, oracle will check in $oracle_home/dbs directory and on windows it will check
in oracle_home/database directory, and the content of pfile is just text based, but
spfile content is in binary format, that is understandable by oracle very well.

Also oracle server always check the spfile or pfile with these sequence :-

SPFILE<SID>.ORA, SPFILE.ORA, PFILE<SID>.ORA,PFILE.ORA


11.What is an index segment

Oracle creates the index segment for an index or an index partition when you issue
the CREATE INDEX statement. In this statement, you can specify storage parameters
for the extents of the index segment and a tablespace in which to create the index
segment. (The segments of a table and an index associated with it do not have to
occupy the same tablespace.) Setting the storage parameters directly affects the
efficiency of data retrieval and storage

12.What is public database link

You can create a public database link for a database. All users and PL/SQL
subprograms in the database can use a public database link to access data and
database objects in the corresponding remote database.
When many users require an access path to a remote Oracle database, an
administrator can create a single public database link for all users in a database.
CREATE PUBLIC DATABASE LINK ...;


13.What is row chaining

if any of the empty row is not sufficient to hold the row. then row is placed in
multiple blocks. it happenes when the block size is small and rows are of large size.
then it cause chaining. Due to chaining performance degrades and will cause more
IOs

14.What is the use of control file

Control file is binary file which is having all the information realted to database.
db_name, maxlogfiles, maxdatafiles, tablespaces information. Without this u cannot
open your database. Init.ora parameter file showing the location of the controlfile.
(or)
control file is a binary file which contains db_name,dbcreated,checkpoint
information,datafiles and logfiles.

15.What is a tablespace

Tablespace is nothing but a logical object comprisiing of one or more data files
which actually stores the data. (or) A tablespace is a collection of one or more
datafile.

16.What is SYSTEM tablespace and when is it created

SYSTEM TABLESPACE USAGE NOTES:

Username - Name of the user
Created - User creation date
Profile - Name of resource profile assigned to the user
Default Tablespace - Default tablespace for data objects
Temporary Tablespace - Default tablespace for temporary objects

Only SYS, SYSTEM and possibly DBSNMP should have their default tablespace set to
SYSTEM.

select USERNAME,
CREATED,
PROFILE,
DEFAULT_TABLESPACE,
TEMPORARY_TABLESPACE
from dba_users
order by USERNAME


Objects in SYSTEM TS
OBJECTS IN SYSTEM TABLESPACE NOTES:


Owner - Owner of the object
Object Name - Name of object
Object Type - Type of object
Tablespace - Tablespace name
Size - Size (bytes) of object

Any user (other than SYS, SYSTEM) should have their objects moved out of the
SYSTEM tablespace

select OWNER,
SEGMENT_NAME,
SEGMENT_TYPE,
TABLESPACE_NAME,
BYTES
from dba_segments
where TABLESPACE_NAME = 'SYSTEM'
and OWNER not in ('SYS','SYSTEM')
order by OWNER, SEGMENT_NAME

17.How to define data block size

The primary block size is defined by the Initiaization parameter DB_BLOCK_SIZE.

18.What is an Oracle sequence

A sequence is a database object created by a user that can be used to generate
unique integers. A typical usage of sequences is to generate primary key values
which are unique for each row.
It is generated and incremented (or decremented) by an internal Oracle routine. It
can be used by multiple users and for multiple tables too. A sequence can be used
instead of writing an application code for sequence-generating routine.


19.Explain the relationship among database, tablespace and data file.What is
schema

Databases, tablespaces and datafiles are closely related, but they have important
differences:

--- A Oracle Database consists of one or more tablespaces
--- Each Table space in an Oracle database consists of one or more files called
datafiles.
--- A database's data is collectively stored in the datafiles that constitute each
tablespace of the database

                          (or)
When a database user is created, a corresponding schema with the same name is
created for that user. A schema is a named collection of objects that include
Tables, Triggers, constraints, Indexes, Views etc. A user can only be associated with
one schema, and that is the same name as the user's. Username and schema are
often used interchangeably.


20.DIFFERENTIATE BETWEEN Latches vs Enqueues

Enqueues are another type of locking mechanism used in Oracle. An enqueue is a
more sophisticated mechanism which permits several concurrent processes to have
varying degree of sharing of "known" resources. Any object which can be
concurrently used, can be protected with enqueues. A good example is of locks on
tables. We allow varying levels of sharing on tables e.g. two processes can lock a
table in share mode or in share update mode
etc.

One difference is that the enqueue is obtained using an OS specific locking
mechanism. An enqueue allows the user to store a value in the lock, i.e the mode in
which we are requesting it. The OS lock manager keeps track of the resources
locked. If a process cannot be granted the lock because it is incompatible with the
mode requested and the lock is requested
with wait, the OS puts the requesting process on a wait queue which is serviced in
FIFO.
Another difference between latches and enqueues is that in latches there is no
ordered queue of waiters like in enqueues.

Latch waiters may either use timers to wakeup and retry or spin (only in
multiprocessors). Since all waiters are concurrently retrying (depending on the
scheduler), anyone might get the latch and conceivably the first one to try might be
the last one to get.


21.What is a latch?

Latches are low level serialization mechanisms used to protect shared data
structures in the SGA. The implementation of latches is operating system
dependent, particularly in regard to whether a process will wait for a latch and for
how long.

A latch is a type of a lock that can be very quickly acquired and freed. Latches are
typically used to prevent more than one process from executing the same piece of
code at a given time. Associated with each latch is a cleanup procedure that will be
called if a process dies
while holding the latch. Latches have an associated level that is used to prevent
deadlocks. Once a process acquires a latch at a certain level it cannot subsequently
acquire a latch at a level that is equal to or less than that level (unless it acquires it
nowait).
What is difference between Logical Standby Database and Physical Standby
database?

The primary functional difference between logical and physical standby database
setups is that logical standby permits you to add additional objects (tables, indexes,
etc) to the database, while physical standby is always an exact structural duplicate
of the master database. The downside, though, is that logical standby is based on
newer technologies (logical standby is new in Oracle 9.2) and tends to be generally
regarded as more tempramental than physical standby.


22.What is the frequency of log Updated..?

1.COMMIT or ROLLABCK
2.time out occurs (3 secs)
3 1/3 of log is full
4.1 mb of redo
5. Checkpoint occurs

23.How do you pin an object.

Use dbms_shared_pool procedure.
EXECUTE DBMS_SHARED_POOL.KEEP(OBJECTNAME);


24.How do you rename a database?
--------------------------------------------------------------------------------

-- To change the name of the database
-- For this script to run properly do the following:

-- Backup the Control fiel to Trace
ALTER DATABASE BACKUP CONTROLFILE TO TRACE;

-- Shutdown the database to make the changes
SHUTDOWN IMMEDIATE;

-- Edit the trace file and change the CREATE CONTROLFILE command
-- CREATE CONTROLFILE REUSE SET DATABASE "NEW_SID_NAME" RESETLOGS
-- (note the SET keyword)

Change the name in Control file and Init.ora
The first line of Control file should be "CREATE CONTROLFILE REUSE SET DATABASE ""
RESETLOGS ARCHIVELOG"

- modify the db_name parameter in the init.ora

-- Startup the datbase nomount with changed PFile
STARTUP NOMOUNT;
-- Execute the create controlfile command.
@create_control.sql;

-- Cancel base recovery of the database
Recover database USING BACKUP CONTROLFILE until cancel;
CANCEL

-- Open resetlogs the database
ALTER DATABASE OPEN RESETLOGS;

-- Rename GLOBAL_NAME to
ALTER DATABASE RENAME GLOBAL_NAME TO ;

-- Create SPFile, IF required give NAME and PATH of the PFILE
CREATE SPFILE FROM PFILE;

select name from v$database;

         (or)

You can change Database my by simple do some steps.

1. Alter Database backup control file to trace;
2. Above step will create a text control file.
3. Change the Database name there and in init.ora file.
4. create new control file by running script (from backup control file)
5. Startup mount
6.open database resetlogs.
And your database name will be changed

25.What is the use of redo log information

Redo log information are used to recover database if it get currept.

26.Explain Oracle memory structure.

The Oracle RDBMS creates and uses storage on the computer hard disk and in
random access memory (RAM). The portion in the computer’s RAM is called memory
structure. Oracle has two memory structures in the computer’s RAM. The two
structures are the Program Global Area (PGA) and the System Global Area (SGA).
The PGA contains data and control information for a single, user process. The SGA is
the memory segment that stores data that the user has retrieved from the database
or data that the user wants to place into the database



27.What are memory structures in Oracle?

The basic memory structures associated with Oracle include:
• System Global Area (SGA), which is shared by all server and background
processes and holds the following:
o Database buffer cache
o Redo log buffer
o Shared pool
o Large pool (if configured)
• Program Global Areas (PGA), which is private to each server and background
process; there is one PGA for each process. The PGA holds the following:
o Stack areas
o Data areas

28.State new features of Oracle 9i.

1.   Dynamic Memomry Management
2.   Default tablespace at the db levele
3.   temporary tablespace at the dba level
4.   Undo tablespace managemnet (auto/manual)


29.What does database do during mounting process?

During database mount process, Oracle would check for the existence of controlfiles
mentioned in init.ora file but it wont check the contents of the controlfile which is
done during the opening of database.

30.What is the view name where i can get the space in MB for tables or views?

select       segment_name,sum(bytes)   from                        dba_segmentswhere
segment_name='TABLE_NAME' AND OWNER='OWNER                  of   the table'group by
segment_name


31.How to DROP an Oracle Database?

You can do it at the OS level by deleting all the files of the database. The files to be
deleted can be found using:

1)   select * from dba_data_files;
2)   select * from v$logfile;
3)   select * from v$controlfile;
4)   archive log list
5)   initSID.ora
6)   In addition you can clean the UDUMP, BDUMP, scripts etc

Clean up the listener.ora and the tnsnames.ora. make sure that the oratab entry is
also removed. (or)
Go To Dbca And Click On Delete Database


32.What is Parallel Server ?
Multiple  instances      accessing   the   same   database   (Only   In   Multi-CPU
environments)



33.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

34.What is a deadlock ? Explain .

Two processes wating to update the rows of a table which are locked by the other
process then deadlock arises.
In a database environment this will often happen because of not issuing 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.


                                       (OR)

A deadlock is a condition where two or more users are waiting for data locked by
each other. Oracle automatically detects a deadlock and resolves them by rolling
back one of the statements involved in the deadlock, thus releasing one set of data
locked by that statement. Statement rolled back is usually the one which detects
the deadlock. Deadlocks are mostly caused by explicit locking because oracle does
not do lock escalation and does not use read locks. Multitable deadlocks can be
avoided by locking the tables in same order in all the applications, thus precluding a
deadlock. (OR)
System waiting for an event that may or may not happens and can be rectified using
round robin algorithm which implemented internally by operating systems

				
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Description: ORACLE BASICS INTERVIEW QUESTIONS