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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.
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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
I`m working as Independent Oracle DBA for
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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.
http://download.oracle.com/docs/cd/B19306_01/server.102
/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.
http://download.oracle.com/docs/cd/B19306_01/server.102
/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
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K
SEGMENT SPACE MANAGEMENT AUTO
ONLINE;
CREATE TABLESPACE part2
DATAFILE 'c:\temp\part02.dbf' SIZE 50M
BLOCKSIZE 8192
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K
SEGMENT SPACE MANAGEMENT AUTO
ONLINE;
CREATE TABLESPACE part3
DATAFILE 'c:\temp\part03.dbf' SIZE 50M
BLOCKSIZE 8192
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K
SEGMENT SPACE MANAGEMENT AUTO
ONLINE;
CREATE TABLESPACE part4
DATAFILE 'c:\temp\part04.dbf' SIZE 50MBLOCKSIZE 8192
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K
SEGMENT SPACE MANAGEMENT AUTO
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);
SELECT table_name, tablespace_name, partitioned
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);
SELECT table_name, tablespace_name, partitioned
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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