Rakesh Soni - Oracle DBA_ Oracle Interview Questions

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Wednesday, October 3, 2007

Oracle Interview Questions

These are the Oracle DBA interview Questions that were

asked to me for Fresh /Assitant Oracle DBA Job.

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1-You have written in your CV that As a DBA u can Test a Backup,

How?

2-You have written in your CV, that you can monitor physical and

logical backup, how?

3-You have written in your CV, that you can Rebuild Index to

rectify segment fragmentation. (Coalesce)

4-You has written in your CV, that you can Automatic Schedule a

logical backup. how?

5-HVM, when it will be decreased? How can I do it? (Truncate

table)

6-Alert log file? What it contains?

7-Control file? What information it contains? When it is read?8- I have lost my Control File & dont have any Backup; Can I start

DB & operate? How? (You create a control file in no mount mode.)

9- Mount- No Mount?

10-SGA? Its Components?

11-Checkpoint? Why Checkpoint? Where its recorded? When its

recorded?

12-LGWR? When it writes?

13-Duties of DBA?

14-Whats Statspack? How can I use Statspack?

15-Methods of Backup (Cold & Hot Backup)?

16 -Why do you want to be DBA? Why Not a Developer?

17-What is RECOVERY Catalog? Why we need it? Complete

command/steps of creating Recovery Catalog? How will it know

about the Primary Database? -What role/Privileges are given to

user when he is connected to Recovery Catalog? -How can I

connect with RMAN? Its Steps?

18-RMAN Incremental Backups? What are Differential &

Cumulative Backups?

19-Write a statement/command for exporting all the objects of

owner HR?

20-Direct=y

21-Standby Databases?

22-RAC?

Oracle 11g DBA Certified

Oracle 10g DBA Certified

About Me

Rakesh Kumar Soni

Karachi, Sindh, Pakistan

More Next Blog Create Blog Sign In

I am writing at my blog for future reference. I am writing Oracle related experiences and stuffs. I have

over 5 years of Oracle DBA experience, I am also Oracle 11g DBA & 10g DBA Certified Professional. If you

want to hire me on Permanent / Contract / Project basis then do contact me at [email protected] or

[email protected] or call me at +92-3009274815.

sh Soni - Oracle DBA: Oracle Interview Questions http://rakeshocp.blogspot.in/2007/10/oracle-interview-quest

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23-Partitioning (List, Range, Hash)

24-If my application is slow, how can we make it efficient, faster?

-How will you tune if application is slow?

25-RMAN Backups?

26-ADDM.

27-AWR.

28-Flashback? What is flashback in 10g?

29-What is command for restoring from recycle bin?

2nd interview.30-Difference between User & Schema?

31-Cluster key? 32- RAC?

33-Stand By database?

33-What are duties of DBA?

34-What is Difference among NOMOUNT & MOUNT & OPEN

modes? When Database will be available for read?

35-What is SGA? And what are its components?

36-How can we allocate SGA? How we can know it proper size?

How should we estimate? How can we calculate size of SGA?

37-If database is running 24 hours a day, 7 days a week when I

come to office in morning what should I do Check? What files,

views, or Services should I check?38-How can you perform Fragmentation in tables?

39-Suppose, if I export table data and then import? Does it

perform fragmentation?

40-Interviewer Asked from me:-Tell me if you are DBA, u left the

office at night, and when u arrive at office in the morning, what

you will check in database?

41-How can you schedule a job?

42-RAID?

43-New feature of 10g.

44-What is Database? RDBMS? Rules?

HR Interview Questions?

1.Tell me more about yourself.

2.Why did you choose this career?

3.Why do you want to work here at ABC Inc.?

4.What would you say is your strength? Your weakness?

5.What did you learn from your last job/internship/educational

experience?

7.Why do you want this job?

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1- You have written in your CV that As a DBA u can Test a

Backup, How?Regularly test the backup & recovery srtategy, becaue it shows the

integrity of the backups, the validity of the backup and recovery

method, and the reduction of the problems before the occur in a

production database.

Testing the backup and recovery plan ensures:

That the backup and recovery methods are sound

Integrity of backups

Ensures that the backup and recovery strategy meets business

needs.

It minimizes problems before they occur in a production

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environment.

It ensures that personnel can react quickly and effectively in

case any errors arise, avoiding a crisis situation.

2- You have written in your CV, that you can monitor

physical and logical backup, how?

http://www.oracle.com/technology/deploy/availability/htdocs

/BR_Overview.htm

A backup is a representative copy of data. This copy can include

important parts of a database such as the control file, redo logs,and datafiles. A backup protects data from application error and

acts as a safeguard against unexpected data loss, by providing a

way to restore original data. Backups are divided into physical

backups and logical backups. Physical backups are copies of

physical database files. The phrase "backup and recovery" usually

refers to the transfer of copied files from one location to another,

along with the various operations performed on these files.

In contrast, logical backups contain data that is exported using SQL

commands and stored in a binary file. Oracle records both

committed and uncommitted changes in redo log buffers. Logical

backups are used to supplement physical backups. Restoring a

physical backup means reconstructing it and making it available tothe Oracle server. To recover a restored backup, data is updated

using redo records from the transaction log. The transaction log

records changes made to the database after the backup was taken.

http://www.oracle.com/technology/deploy/availability/htdocs

/BR_Overview.htm

Types of Backup

There are two kinds of database backups available to us physical

backups and logical backups.

Physical Backupis an actual physical copy of the files of the

database copied from one location to another.

Logical Backupis a copy of the data in the database but not a

copy of the physical files.

Cold Backup

A cold backup is a physical backup.

During a cold backup the database is closed and not available to

users. All files of the database are copied (image copy). The

datafiles do not change during the copy so the database is in sync

upon restore.

Used when: Service level allows for some down time for backup

Hot Backup

A hot backup is a physical backup. In a hot backup the database

remains open and available to users. All files of the database arecopied (image copy). There may be changes to the database as the

copy is made and so all log files of changes being made during the

backup must be saved too. Upon a restore, the changes in the log

files are reapplied to bring the database in sync.

Used when: A full backup of a database is needed Service level

allows no down time for the backup

Logical Backup

A logical backup is an extract of the database. All SQL statements

to create the objects and all SQL statements to populate the

objects are included in the extract. Oracle provides a utility export,

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to create the extract. A partner utility, import, is used to bring the

data back into the database.

A logical backup can be done at the table, schema(or proxy owner),

or database level. That is, we can extract only a list of specified

tables, a list of specified schemas or the full database.

Used to:

Move or archive a database

Move or archive a table(s)

Move or archive a schema(s)Verify the structures in the database.

3- You have written in your CV, that you can Rebuild Index

to rectify segment fragmentation. (Coalesce)

Index:An index is a tree structure that allows direct access to a

row in table.

Rebuild:An index contains deleted entries and should be rebuild,

such a case of index on Order number of an Orders tables, where

completed orders are deleted & new orders with higher numbers

are added.

ALTER INDEX orders_index REBUILDTABLESPACE index02;

Above command moves an index to a different TableSpace.

Improve space utilization by removing deleted entries.

COALESCE:If you encounter index fragmentation then you can

rebuild or coalesce. Coalescing an index is a block rebuild that is

performed online.

I.e. Merging B-tree index leaf blocks that can be freed for reuse.

ALTER INDEX hr.employees_idx COALESE;

----------------------------------------------------------

When one must rebuild Indexes, read the at the forums.oracle.com

at below thread.

http://forums.oracle.com/forums

/thread.jspa?threadID=580451&tstart=0

4- You has written in your CV, that you can Automatic

Schedule a logical backup. how?

http://rakeshocp.blogspot.com/2007/09/batch-file-scripts.html

Visit above blog page for Automatic Scheduling of logical

backup.

5- HVM, when it will be decreased? How can I do it?

(Truncate table)

High water mark:The high water mark is the boundary between

used and unused space in a segment. As requests for new free

blocks that cannot be satisfied by existing free lists are received,

the block to which the high water mark points becomes a used

block, and the high water mark is advanced to the next block. In

other words, the segment space to the left of the high water mark

is used, and the space to the right of it is unused.

The high water mark is divides a segmentinto used blocksfree

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blocks

Blocks below the high water mark (used blocks) have at least once

contained data. This data might have been deleted.

Since Oracle knows that blocks beyond the high water mark don't

have data, it only reads blocks up to the high water mark in a full

table scan.

Oracle keeps track of the high water mark for a segmentin the

segment header.

Moving the high water mark

In normal DB operations, the high water mark only movesupwards, not downwards. The exceptions being the truncate.

If there is a lot of free space below the high water mark, one might

consider to use alter table move statements. See On shrinking

table sizes.

http://www.adp-gmbh.ch/blog/2005/july/20.html

truncate table table_name;

truncate cluster cluster_name;

A statement like delete from tablename deletes all records in the

table, but it does not free any space (see On table sizes). In order

to free the space as well, use truncate. However, a truncate can notbe rolled back.

Truncate Table: Basically, a truncate statement resets the high

water markto its initial position.

A truncate statement cannot be used on a synonym.

Ways for reseting high water mark.

- export/import

-CTAS (Create table as select)

- dbms_redefinition

6- Alert log file? What it contains?

Location Defined by BACKGROUND_DUMP_DEST

Alert log file should be the 1st place when diagnosing day-to-day

operations or errors.

Keeps record of

When DB was started & shutdown

List of all non default initialization parameters.

Startup of Background processes.

Log sequence number LGWR writing to.

Info abt log switch

Creation of tablespace & undo segments

Alter statement that has been issued.

Information abt errors messages ora-600 & extent errors.

7- Control file? What information it contains? When it is

read?

Small binary file

Defines current state of physical database.

Required.

At mount state during startup

To operate the database

Linked to a single database.

Loss may require recovery.

Control file contains


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Database Name & Identified

Timestamp of DB creation

Tablespace names

Names & location of data files & online redo log files

Current online redo log file information

Checkpoint information

Begin & end of undo segments

Redo log archive information

Backup Information

Read at the Mount mode of the database.

8- I have lost my Control File & dont have any Backup; Can

I start DB & operate? How? (You create a control file in no

mount mode.)

Yes, we can operate the database, follow the steps below:

Start instance if necessary.

Shut down instance if start failed.

Start the Instance in Mount mode.

Run the trace file script to recreate the control file.

Determine if full back up is required and perform one if

necessary.

Ensure that instance is started & database is open.

http://www.orafaq.com/wiki/Control_file_recovery

http://download.oracle.com/docs/cd/B19306_01/server.102

/b14231/control.htm#i1006360

Steps for Creating New Control Files

Complete the following steps to create a new control file.

1. Make a list of all datafiles and redo log files of the database.

If you follow recommendations for control file backups as discussed

in "Backing Up Control Files" , you will already have a list of

datafiles and redo log files that reflect the current structure of the

database. However, if you have no such list, executing the following

statements will produce one.SELECT MEMBER FROM

V$LOGFILE;SELECT NAME FROM V$DATAFILE; SELECT VALUE

FROM V$PARAMETER WHERE NAME = 'control_files';

If you have no such lists and your control file has been damaged so

that the database cannot be opened, try to locate all of the

datafiles and redo log files that constitute the database. Any files

not specified in step 5 are not recoverable once a new control file

has been created. Moreover, if you omit any of the files that make

up the SYSTEM tablespace, you might not be able to recover the

database.

2. Shut down the database.

If the database is open, shut down the database normally ifpossible. Use the IMMEDIATE or ABORT clauses only as a last

resort.

3. Back up all datafiles and redo log files of the database.

4. Start up a new instance, but do not mount or open the

database:

5. STARTUP NOMOUNT

6.

7. Create a new control file for the database using the CREATE


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CONTROLFILE statement.

When creating a new control file, specify the RESETLOGS clause if

you have lost any redo log groups in addition to control files. In this

case, you will need to recover from the loss of the redo logs (step

8). You must specify the RESETLOGS clause if you have renamed

the database. Otherwise, select the NORESETLOGS clause.

8. Store a backup of the new control file on an offline storage

device. See "Backing Up Control Files" for instructions for creating a

backup.

9. Edit the CONTROL_FILES initialization parameter for the

database to indicate all of the control files now part of your

database as created in step 5 (not including the backup control

file). If you are renaming the database, edit the DB_NAME

parameter in your instance parameter file to specify the new name.

10. Recover the database if necessary. If you are not recovering

the database, skip to step 9.

If you are creating the control file as part of recovery, recover the

database. If the new control file was created using the

NORESETLOGS clause (step 5), you can recover the database withcomplete, closed database recovery.

If the new control file was created using the RESETLOGS clause,

you must specify USING BACKUP CONTROL FILE. If you have lost

online or archived redo logs or datafiles, use the procedures for

recovering those files.

See Also:

Oracle Database Backup and Recovery Basics and Oracle Database

Backup and Recovery Advanced User's Guide for information about

recovering your database and methods of recovering a lost control

file

11. Open the database using one of the following methods:

o If you did not perform recovery, or you performed complete,

closed database recovery in step 8, open the database normally.

o ALTER DATABASE OPEN;

o If you specified RESETLOGS when creating the control file, use

the ALTER DATABASE statement, indicating RESETLOGS.

o ALTER DATABASE OPEN RESETLOGS;

The database is now open and available for use.


/b14231/control.htm#i1006360

====================

Trace File:When one of the Oracle background processes (such as dbwr, lgwr,

pmon, smon and so on ) encounter an exception, they will write a

trace file.

These trace files are also recorded in the alert.log.

Trace files are also created for diagnostic dump events.

An ORA-00600 error also produces a trace file.

9- Mount- No Mount?

NOMOUNT:An oracle instance can be started in NOMOUNT stage

only during database creation or the recreation of control files.

MOUNT: To perform specific maintenance operations, dont open


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the database.

Renaming datafiles

Enabling & disabling archive redo log file archiving options

Performing full database recovery

10- SGA? Its Components?

SGA: Shared Global Area is allocated at instance startup, and is

fundamental component of Oracle Instance.

Size defined by SGA_MAX_SIZE.Components

Shared Pool (SHARED_POOL_SIZE)

Database Buffer Cache (DB_CACHE_SIZE)

Redo Log Buffer (LOG_BUFFER)Additional Components

Large Pool

Java Pool

11- Checkpoint? Why Checkpoint? Where its recorded?

When its recorded?

Database Checkpoint:Checkpoints are you used to determine

where recovery should start.

Checkpoint position where recovery should startCheckpoint queue link list of dirty blocks

The position in the redo log where recovery should start is referred

as to as the checkpoint position.

Types of Checkpoint

1-Full check point

All dirty buffers are written

Shutdown normal, immediate, or transactional

Alter System Checkpoint

2-Incremental Checkpoint

3-Partial Checkpoint

Alter tablespace begin backup

Alter tablespace offline normal

When a checkpoint occurs, Oracle must update the headers of all

datafiles to record the details of the checkpoint. This is done by the

CKPT process. The CKPT process does not write blocks to disk;

DBWn always performs that work.

Every 3 seconds CKPT records the RBA from the oldest entry to in

the checkpoint queue in the control file. This RBA represents the

point in the redo log at which instance recovery is to begin after an

instance failure. It can do this because all of the data blocks

represented in prior redo records are guaranteed to have been

written do disk by DBWn

On the event on a log switch, does CKPT also write this informationto the header of the datafiles.

12- LGWR? When it writes?

LGWR performs sequential writes from the Redo Log Buffer to the

Online redo Log files under the following situations

At Commit

When the Redo Log Buffer is one-third full

When there is more than 1 MB of changes recorded in the Redo

Log Buffer

Befoere DBW writes modified blocks

Every 3 seconds


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13- Duties of DBA?

To plan & Create Databases

To Manage Database Availability

To Manage Physical & Logical Structure

To Manage Storage based on design

To manage security

Network Administration

Backup & Recovery

Database Tuning

14- Whats Statspack? How can I use Statspack?

STATSPACK: STATSPACK is a performance diagnosis tool, available

since Oracle8i. STATSPACK can be considered BSTAT/ESTAT's

successor, incorporating many new features. STATSPACK is a

diagnosis tool for instance-wide performance problems; it also

supports application tuning activities by providing data which

identifies high-load SQL statements. STATSPACK can be used both

proactively to monitor the changing load on a system, and also

reactively to investigate a performance problem.

UTLBSTAT - UTLESTATThe BSTAT-ESTAT utilities capture information directly from the

Oracle's in-memory structures and then compare the information

from two snapshots in order to produce an elapsed-time report

showing the activity of the database. If we look inside utlbstat.sql

and utlestat.sql, we see the SQL that samples directly from the

view: V$SYSSTAT;

insert into stats$begin_stats select * from v$sysstat;

insert into stats$end_stats select * from v$sysstat;

How can I use Statspack

Create PERFSTAT Tablespace

The STATSPACK utility requires an isolated tablespace to obtain all

of the objects and data. For uniformity, it is suggested that the

tablespace be called PERFSTAT, the same name as the schema

owner for the STATSPACK tables. It is important to closely watch

the STATSPACK data to ensure that the stats$sql_summary table is

not taking an inordinate amount of space.

SQL> CREATE TABLESPACE perfstat

DATAFILE '/u01/oracle/db/AKI1_perfstat.dbf' SIZE 1000M REUSE

EXTENT MANAGEMENT LOCAL UNIFORM SIZE 512K

SEGMENT SPACE MANAGEMENT AUTO

PERMANENT

ONLINE;Run catdbsyn.sql as SYS

Run dbmspool.sql as SYS

$ cd $ORACLE_HOME/rdbms/admin$ sqlplus "/ as sysdba"SQL>

start spcreate.sql

Adjusting the STATSPACK Collection Level

STATSPACK has two types of collection options, level and threshold.

The level parameter controls the type of data collected from Oracle,

while the threshold parameter acts as a filter for the collection of

SQL statements into the stats$sql_summary table.

SQL> SELECT * FROM stats$level_description ORDER BY


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snap_level;

Level 0: This level captures general statistics, including rollback

segment, row cache, SGA, system events, background events,

session events, system statistics, wait statistics, lock statistics, and

Latch information.

Level 5:This level includes capturing high resource usage SQL

Statements, along with all data captured by lower levels.

Level 6:This level includes capturing SQL plan and SQL plan usage

information for high resource usage SQL Statements, along with alldata captured by lower levels.

Level 7:This level captures segment level statistics, including

logical and physical reads, row lock, itl and buffer busy waits, along

with all data captured by lower levels.

Level 10:This level includes capturing Child Latch statistics, along

with all data captured by lower levels.

15- Methods of Backup (Cold & Hot Backup)?

A cold backup, also called an offline backup, is a database backup

when the database is offline and thus not accessible for updating.

This is the safest way to back up because it avoids the risk of

copying data that may be in the process of being updated.However, a cold backup involves downtime because users cannot

use the database while it is being backed up.

When system downtime must be minimized, a hot backup can

provide an alternative to the cold backup. A hot backup can be

done even as users access the database, but some method must be

used to ensure that data being updated is noted and can be copied

when the update is complete.

16 -Why do you want to be DBA? Why Not a Developer?

I think being an Oracle DBA is really rewarding. It can be a highly

demanding job, but I feel that this is part of the exciting challenge

of being a DBA. But I choose this path for myself and I am really

happy with it. It is an exciting and rewarding job.

17- What is RECOVERY Catalog? Why we need it? Complete

command/steps of creating Recovery Catalog? How will it

know about the Primary Database? -What role/Privileges

are given to user when he is connected to Recovery Catalog?

-How can I connect with RMAN? Its Steps?

What is RECOVERY Catalog

Recovery Catalog is schema that is created in a separate

tablespace.

RMAN propagates information about the database structure,

archived redo log files, and datafile copies into the recovery catalog

from the control file of target database.

http://www.idevelopment.info/data/Oracle/DBA_tips/RMAN_9i

/RMAN9_4.shtml

To use RMAN, a recovery catalog is not necessary. Remember that

RMAN will always use the control file of the target database to store

backup and recovery operations. To use a recovery catalog, you will

first need to create a recovery catalog database and create a

schema for it. The catalog (database objects) will be located in the

default tablespace of the schema owner. Please note that the owner

of the catalog cannot be the SYS user.


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The recovery catalog database should be created on a different

host, on different disks, and in a different database from the target

databse you will be backing up. If you do not, the benefits of using

a recovery catalog are lost if you loose the database and need to

restore.

The first step is to create a database for the recovery catalog. For

the purpose of this example, I created an Oracle 9.2.0 database

named CATDB. The database has the following installed:

You have access to the SYS password for the database.

A temporary tablespace named TEMP already exists.

A normal tablespace named TOOLS exists and will be used to

store the recovery catalog.

The database is configured in the same way as all normal

databases, for example, catalog.sql and catproc.sql have been

successfully run.

Now, let's create the recovery catalog:

1. Start SQL*Plus and then connect with SYSDBA privileges to thedatabase containing the recovery catalog:

% sqlplus "sys/change_on_install as sysdba"

2. Create a user and schema for the recovery catalog:

3. SQL> CREATE USER rman IDENTIFIED BY rman

4. DEFAULT TABLESPACE tools

5. TEMPORARY TABLESPACE temp

6. QUOTA UNLIMITED ON tools;

7.

User created.

8. Grant the RECOVERY_CATALOG_OWNER role to the schema

owner. This role provides the user with privileges to maintain and

query the recovery catalog: 9.

SQL> GRANT RECOVERY_CATALOG_OWNER TO rman;

10. Grant succeeded.

11. Grant other desired privileges to teh RMAN user:

12. SQL> GRANT CONNECT, RESOURCE TO rman;

13. Grant succeeded.

14. After creating the catalog owner you should now create the

catalog itself by using the CREATE CATALOG command within the

RMAN interface. This command will create the catalog in the default

tablespace of the catalog owner. you will need to connect to the

database that will contain the catalog as teh catalog owner as

follows:

15. % rman catalog rman/rman@catdb16.

17. Recovery Manager: Release 9.2.0.1.0 - Production

18.

19. Copyright (c) 1995, 2002, Oracle Corporation. All rights

reserved.

20.

21. connected to recovery catalog databaserecovery catalog is not

installed

22. Now, run the CREATE CATALOG command to create the catalog.

Note that this process can take several minutes to complete.

23. RMAN> create catalog;


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24. recovery catalog created

Registering the Target Database

Before using RMAN using a recovery catalog, you will need to

register the taget database(s) in the recovery catalog. RMAN will

obtain all information it needs to register the target database from

the database itself.

As long as each target database has a distinct DBID, you can

register more than one target database in the same recovery

catalog. Each database registered in a given catalog must have aunique database identifier (DBID), but not necessarily a unique

database name.

You can use either the command-line utilities provided by RMAN or

the Oracle Enterprise Manager GUI to register the target database.

For the purpose of this example, I will be using the command-line

utilities. I will be registering a database named TARGDB to a

recovery catalog within a database named CATDB. The target

database must be either mounted or opened in order to register it.

% . oraenv

ORACLE_SID = [TARGDB] ? TARGDB

% rman target backup_admin/backup_admin catalogrman/rman@catdb

Recovery Manager: Release 9.2.0.1.0 - Production

Copyright (c) 1995, 2002, Oracle Corporation. All rights reserved.

connected to target database: TARGDB (DBID=2457750772)

connected to recovery catalog database

RMAN> register database;

database registered in recovery catalog

starting full resync of recovery catalog

full resync complete

18- RMAN Incremental Backups? What are Differential &

Cumulative Backups?

Incremental backup is a backup that includes only those blocks that

have changed since the previous backup.

click the link below for details about Differential and Cumulative

Backups.

http://download-uk.oracle.com/docs/cd/B19306_01

/backup.102/b14191/rcmconc1005.htm

19- Write a statement/command for exporting all the

objects of owner HR?

Exp user=hr/hr full=y direct=y

20- Direct=y

Determines whether to use direct or conventional path export.

Direct path exports bypass the SQL command, thereby enhancing

performance

21- Standby Databases?

A standby database is a transactionally consistent copy of the

primary database. A standby database is initially created from a

backup copy of the primary database. Once created, Data Guard

automatically maintains the standby database by transmitting


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primary database redo data to the standby system and then

applying the redo logs to the standby database.

Similar to a primary database, a standby database can be either a

single-instance Oracle database or an Oracle Real Application

Clusters database.

A standby database can be either a physical standby database or a

logical standby database:

Physical standby database

Provides a physically identical copy of the primary database, withon-disk database structures that are identical to the primary

database on a block-for-block basis. The database schema,

including indexes, are the same. A physical standby database is

kept synchronized with the primary database by recovering the

redo data received from the primary database.

Logical standby database

Contains the same logical information as the production database,

although the physical organization and structure of the data can be

different. It is kept synchronized with the primary database by

transforming the data in the redo logs received from the primary

database into SQL statements and then executing the SQL

statements on the standby database. A logical standby databasecan be used for other business purposes in addition to disaster

recovery requirements. This allows users to access a logical

standby database for queries and reporting purposes at any time.

Thus, a logical standby database can be used concurrently for data

protection and reporting.

For more details about Stand By databases visit the link below.


/b14239/concepts.htm

22- RAC?

Real Application Clusters harnesses the processing power of

multiple interconnected computers. Real Application Clusters

software and a collection of hardware known as a cluster unite the

processing power of each component to create a robust computing

environment.

You can use Real Application Clusters to deliver high performance,

increased throughput, and high availability. Before deploying Real

Application Clusters, however, you should understand Real

Application Clusters processing.

In Real Application Clusters environments, all active instances can

concurrently execute transactions against a shared database. Real

Application Clusters coordinates each instance's access to theshared data to provide data consistency and data integrity.

Harnessing the power of clusters offers obvious advantages. A

large task divided into subtasks and distributed among multiple

nodes is completed sooner and more efficiently than if you

processed the entire task on one node. Cluster processing also

provides increased performance for larger workloads and for

accommodating rapidly growing user populations.

For more details visit the link below.

http://download-uk.oracle.com/docs/cd/B10501_01/rac.920


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/a96597/psintro.htm

23- Partitioning (List, Range, Hash)

More details: http://www.devarticles.com/c/a/Oracle

/Partitioning-in-Oracle/

Partitioning provides facilities for implementing large, scalable

applications. Enables control over tables & indexes at a lower level

of granularity than is possible with basic enterprise edition.

CREATE TABLESPACE part1

DATAFILE 'c:\temp\part01.dbf' SIZE 50

MBLOCKSIZE 8192



ONLINE;


DATAFILE 'c:\temp\part02.dbf' SIZE 50M

BLOCKSIZE 8192



ONLINE;


DATAFILE 'c:\temp\part03.dbf' SIZE 50M

BLOCKSIZE 8192



ONLINE;


DATAFILE 'c:\temp\part04.dbf' SIZE 50MBLOCKSIZE 8192



ONLINE;

HASH Partitioning

Hash Partitioning, which maps data to partitions based on a

hashing algorithm, evenly distributing data between the partitions.

This is typically used where ranges aren't appropriate, i.e.

customer number, product ID

Enables partitioning of data that does not lend itself to range or list

partitioning.To view the numbers Oracle uses for hashing:SELECT program, sql_hash_value, prev_hash_value FROM

gv$session;

CREATE TABLE hash_part (

prof_history_id NUMBER(10),

person_id NUMBER(10) NOT NULL,

organization_id NUMBER(10) NOT NULL,

record_date DATE NOT NULL,

prof_hist_comments VARCHAR2(2000))

PARTITION BY HASH (prof_history_id)

PARTITIONS 3


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STORE IN (part1, part2, part3);

desc prof_hist

SELECT table_name, tablespace_name, partitioned

FROM user_tables;

desc user_tab_partitions

SELECT partition_name, tablespace_nameFROM user_tab_partitions;

---------------------------------------------------------------------------

LIST Partitioning

Explicitly controls how rows map to partitions. You do this by

specifying a list of discrete values for the partitioning key in the

description for each partition.

CREATE TABLE list_part (

deptno NUMBER(10),

deptname VARCHAR2(20),

quarterly_sales NUMBER(10,2),state VARCHAR2(2))

PARTITION BY LIST(state)

(PARTITION q1_northwest VALUES ('OR', 'WA')

TABLESPACE part1,

PARTITION q1_southwest VALUES ('AZ', 'CA', 'NM')

TABLESPACE part2,

PARTITION q1_northeast VALUES ('NY', 'VT', 'NJ')

TABLESPACE part1,

PARTITION q1_southeast VALUES ('FL', 'GA')

TABLESPACE part2,

PARTITION q1_northcent VALUES ('MN', 'WI')

TABLESPACE part1,

PARTITION q1_southcent VALUES ('OK', 'TX')

TABLESPACE part2);


FROM user_tables;

SELECT partition_name, tablespace_name, high_valueFROM

user_tab_partitions;

INSERT INTO list_part VALUES (10, 'A', 1000, 'OR');

INSERT INTO list_part VALUES (20, 'B', 1000, 'AZ');

INSERT INTO list_part VALUES (10, 'A', 1000, 'WA');

INSERT INTO list_part VALUES (20, 'B', 1000, 'WA');INSERT INTO list_part VALUES (10, 'A', 1000, 'AZ');

INSERT INTO list_part VALUES (20, 'B', 1000, 'CA');

COMMIT;

SELECT * FROM list_part;

SELECT * FROM list_part PARTITION(q1_northwest);

---------------------------------------------------------------------------

RANGE Partition

Range Partitioning, which maps data to partitions based on a range

of column values (usually a date column)


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CREATE TABLE range_part (prof_history_id NUMBER(10),

person_id NUMBER(10) NOT NULL,

organization_id NUMBER(10) NOT NULL,

record_date DATE NOT NULL,

ph_comments VARCHAR2(200))

PARTITION BY RANGE(record_date) (

PARTITION yr0

VALUES LESS THAN (TO_DATE('01-JAN-2000','DD-MON-YYYY'))

TABLESPACE part1,PARTITION yr1 VALUES LESS THAN (TO_DATE('01-JAN-2001','DD-

MON-YYYY')) TABLESPACE part2,

PARTITION yr2 VALUES LESS THAN (TO_DATE('01-JAN-2002','DD-

MON-YYYY'))

TABLESPACE part3,

PARTITION yr9 VALUES LESS THAN (MAXVALUE)

TABLESPACE part4);


FROM user_tables;

SELECT partition_name, tablespace_name, high_valueFROM user_tab_partitions;

24- If my application is slow, how can we make it efficient,

faster? -How will you tune if application is slow?

25- RMAN Backups?

RMAN 9i

http://download-uk.oracle.com/docs/cd/B10501_01/server.920

/a96566/rcmintro.htm

26- ADDM.

ADDM: Automatic database diagnostic monitor. ADDM enables

Oracle to diagnose its own performance problems. For example,

ADDM identifies the most resource intensive SQL statements and

passes that statement to the SQL tuning advisor.

ADDM automatically monitors the state of the database at short,

regular intervals (by default: 30 mins) which leads to database

performance diagnostics. It promises that you can forget all of your

scripts that link the many v$ views. ADDM can be run from

Enterprise Manager or through a PL/SQL interface.

SQL tuning advisor In my last column, I focused on one of Oracle

Database 10g's quick wins for DBAsusing the new SQL Tuning

Advisor to quickly tune poorly performing SQL statementsandtouched only briefly on the new built-in diagnostic engine,

ADDM details http://www.oracle-base.com/articles

/10g/AutomaticDatabaseDiagnosticMonitor10g.php

27- AWR.

AWR automatic workload repository looks periodically at the system

performance (by default every 60 minutes) and stores the

information found (by default up to 7 days). This allows retrieving

information about workload changes and database usage patterns.

This information is the basis for all self-management decisions. For


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example, it is thus possible to identify the SQL statements that

have the

larges CPU consumption

most buffer gets

disk reads

most parse calls

shared memory

The data is fed from MMON.

The information is stored in the sysauxtablespace.

28- Flashback? What is flashback in 10g?

With Oracle's flashback, it's possible to sort of travel back in time.

That is, flashback provides a means to see data that was altered

through DDL operations and the state of database objects that

were changed with DML operations. Oracle subcategorises

flashback into three categories: Flashback queryGet previous data

with the as of clause of a select statement. See Flashback query

example 1.

Flashback version queryGet changes of data between a time

interval using the versions between clause of a select statement.

See Flashback version query example 1.

Flashback transaction queryFind changes of a specific transactionthrough the flashback_transaction_query view. See Flashback

transaction version query example 1. Flashback Table

Flashback dropUndrops a dropped table.

flashback database In order to make flashback possible, Oracle

uses undo.

http://www.adp-gmbh.ch/ora/admin/flashback

/version_query_ex_1.html

29- What is command for restoring from recycle bin?

To reinstate the table, all you have to do is use the FLASHBACK

TABLE command:

SQL> FLASHBACK TABLE RECYCLETEST TO BEFORE DROP;

PURGE RECYCLEBIN;But what if you want to drop the table

completely, without needing a flashback feature? In that case, you

can drop it permanently using:

DROP TABLE RECYCLETEST PURGE;

This command will not rename the table to the recycle bin name;

rather, it will be deleted permanently, as it would have been

pre-10g.

2nd interview.30- Difference between User & Schema?

A schema is a collection of database objects. A schema is owned by

a database user and has the same name as that user. Schema

objects are the logical structures that directly refer to the

database's data. Schema objects include structures like tables,

views, and indexes. (There is no relationship between a tablespace

and a schema. Objects in the same schema can be in different

tablespaces, and a tablespace can hold objects from different

schemas.)

31- Cluster key?


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important database information, such as the location of the

database datafiles.

In the mount stage, Oracle determines the location of the datafiles,

but does not yet open them. Once the datafile locations have been

identified, the database is ready to be opened.

Some forms of recovery require that the database be opened in

mount stage.

OPEN MODE

The last startup step for an Oracle database is the open stage.When Oracle opens the database, it accesses all of the datafiles

associated with the database. Once it has accessed the database

datafiles, Oracle makes sure that all of the database datafiles are

consistent.

35- What is SGA? And what are its components?

System Global Area: The System Global Area (SGA) is a shared

memory region that contains data and control information for one

Oracle instance. Oracle allocates the SGA when an instance starts

and deallocates it when the instance shuts down. Each instance has

its own SGA.

Users currently connected to an Oracle database share the data inthe SGA. For optimal performance, the entire SGA should be as

large as possible (while still fitting in real memory) to store as

much data in memory as possible and to minimize disk I/O.

SGA Components: The information stored in the SGA is divided

into several types of memory structures, including the database

buffers, redo log buffer, and the shared pool.

Database Buffer Cache of the SGA:Database buffers store the

most recently used blocks of data. The set of database buffers in an

instance is the database buffer cache. The buffer cache contains

modified as well as unmodified blocks. Because the most recently

(and often, the most frequently) used data is kept in memory, less

disk I/O is necessary, and performance is improved.

Redo Log Buffer of the SGA:The redo log buffer stores redo

entriesa log of changes made to the database. The redo entries

stored in the redo log buffers are written to an online redo log,

which is used if database recovery is necessary. The size of the

redo log is static.

Shared Pool of the SGA:The shared pool contains shared

memory constructs, such as shared SQL areas. A shared SQL area

is required to process every unique SQL statement submitted to a

database. A shared SQL area contains information such as the

parse tree and execution plan for the corresponding statement. A

single shared SQL area is used by multiple applications that issue

the same statement, leaving more shared memory for other uses.

36- How can we allocate SGA? How we can know it proper

size? How should we estimate? How can we calculate size of

SGA?

Check SGA Size Tips at following links.

http://www.dba-oracle.com/t_sga_sizing.htm

38- How can you perform Fragmentation in tables?

(No Comments)

check this link for 10g Shrink. http://www.dbazine.com/blogs/blog-

cf/chrisfoot/blogentry.2005-09-10.8045550726


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39-Suppose, if You export table data and then import? Does

it perform fragmentation?

Yes..

40- Interviewer Asked from me:-Tell me if you are DBA, u

left the office at night, and when u arrive at office in the

morning, what you will check in database?

(No Comments)

I have recently joined a Company, and we have a Checklist that Iused to check in the morning, that containts:

Primary Database:

* OracelServiceABC

* OracleListnerABC

* ArchivedLogSequence #

Backups:

* HOT BACKUPS

* Export Full Database

Standby Databases:

* OracelServiceABCYZ

* OracleListnerABCYZ

* ArchivedLogSequence #* DataGuard Status

41- How can you schedule a job?

(No comments)

You can check in my blog for schedule a batch job.

http://rakeshocp.blogspot.com/2007/09/batch-file-scripts.html

42- RAID?

In computing, specifically computer storage, a Redundant Array of

Independent Drives (or Disks), also known as Redundant Array of

Inexpensive Drives (or Disks), (RAID) is an umbrella term for data

storage schemes that divide and/or replicate data among multiple

hard drives. RAID can be designed to provide increased data

reliability or increased I/O performance, or both.

Follow the links below for RAID information

http://www.ecs.umass.edu/ece/koren/architecture

/Raid/raidhome.html

http://en.wikipedia.org/wiki/RAID

http://www.dba-oracle.com/oracle_tips_raid_usage.htm

43- New feature of 10g for DBAz?

CHeck 10g new features for DBAz http://www.oracle.com

/technology/pub/articles/10gdba/index.html

44- What is Database? RDBMS? Rules?

DATABASE:A collection of information organized in such a way

that a computer program can quickly select desired pieces of data.

RDBMS:a type of database management system (DBMS) that

stores data in the form of related tables. Relational databases are

powerful because they require few assumptions about how data is

related or how it will be extracted from the database. As a result,

the same database can be viewed in many different ways. An

important feature of relational systems is that a single database

can be spread across several tables. This differs from flat-file


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databases, in which each database is self-contained in a single

table.

Almost all full-scale database systems are RDBMS's. Small

database systems, however, use other designs that provide less

flexibility in posing queries.

Rules:Codd's 12 rules are a set of 12 rules proposed by Edgar F.

Codd, a pioneer of the relational model for databases, designed to

define what is required from a database management system in

order for it to be considered relational i.e and RDBMS. visit the linkbelow for Codd's 12 rules.

http://en.wikipedia.org/wiki/Codd

I have tried my level best to help Fresh DBAz to get an idea of

Questions that are mostly asked for fresh DBA job.

I couldn't answer few questions thats why i have answered no

comments in Answer.

Regards!!

Rakesh Kumar Soni.

Posted by Rakesh Kumar Soni at 8:41 AM

7 comments:

Srisaid...

thats a pretty good collection of questions.sure u must have

spent a good time on it.good effort ........keep it up......

October 9, 2007 at 12:45 PM

Rakesh Kumar Sonisaid...

Thanks Sri!!

October 10, 2007 at 10:04 AM

shivamsaid...

Thanks Rakesh for sharing knowledge.Good Stuff

October 12, 2007 at 2:36 PM

Sidsaid...

Good Job my friend...

Siddiq.

February 2, 2008 at 2:07 PM

meenakshisaid...

very nice collection of questions my dear.keep it up.thnx

regards

February 20, 2008 at 12:44 AM

NARASIMHAsaid...

thanxs rakesh u done a very good job.. this help a lot... keep it

up.

August 10, 2010 at 4:02 AM

maxdiona03said...

Hi


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October 5, 2010 at 2:16 AM


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