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Network Administrator Preparation Questions

Question # 1
Who is network administrator?
Network administrator is responsible for the maintenance of computer hardware and software systems that make up a computer network including the maintenance and monitoring of active data network or converged infrastructure and related network equipment.
Network administrators are generally mid-level support staff within an organization and do not typically get involved directly with users. Network administrators focus on network components within a company's LAN/WAN infrastructure ensuring integrity. Depending on the company and its size, the network administrator may also design and deploy networks.

Question # 2
What is network management?
Network management is the operation, administration, maintenance, and provisioning (OAMP) of networked systems. Network management is essential to command and control practices and is generally carried out of a network operations center.

Question # 3
List the layers of the OSI reference model?
There are 7 OSI reference layers:
*    Physical Layer
*    Data Link Layer
*    Network Layer
*    Transport Layer
*    Session Layer
*    Presentation Layer
*    Application Layer

Question # 4
Explain routers?
Routers can connect two or more network segments. These are intelligent network devices that store information in its routing table such as paths, hops and bottlenecks. With this info, they are able to determine the best path for data transfer. Routers operate at the OSI Network Layer.

Question # 5
Describe point to point link?
Anonymous FTP is a way of granting user access to files in public servers. Users that are allowed access to data in these servers do not need to identify themselves, but instead log in as an anonymous guest.

Question # 6
What is link?

A link refers to the connectivity between two devices. It includes the type of cables and protocols used in order for one device to be able to communicate with the other.

Question # 7
Explain backbone network?
A backbone network is a centralized infrastructure that is designed to distribute different routes and data to various networks. It also handles management of bandwidth and various channels.

Question # 8
Define LAN?
LAN is short for Local Area Network. It refers to the connection between computers and other network devices that are located within a small physical location.

Question # 9
Define node?
A node refers to a point or joint where a connection takes place. It can be computer or device that is part of a network. Two or more nodes are needed in order to form a network connection.

Question # 10
Explain subnet mask?
A subnet mask is combined with an IP address in order to identify two parts: the extended network address and the host address. Like an IP address, a subnet mask is made up of 32 bits.

Question # 11
Explain the maximum length allowed for a UTP cable?
A single segment of UTP cable has an allowable length of 90 to 100 meters. This limitation can be overcome by using repeaters and switches.

Question # 12
What can be considered as good passwords?
Good passwords are made up of not just letters, but by combining letters and numbers. A password that combines uppercase and lowercase letters is favorable than one that uses all upper case or all lower case letters. Passwords must be not words that can easily be guessed by hackers, such as dates, names, favorites, etc. Longer passwords are also better than short ones.

Question # 13
Define the number of network IDs in a class C network?
For a Class C network, the number of usable Network ID bits is 21. The number of possible network IDs is 2 raised to 21 or 2,097,152. The number of host IDs per network ID is 2 raised to 8 minus 2, or 254.

Question # 14
Tell me what happens when you use cables longer than the prescribed length?
Cables that are too long would result in signal loss. This means that data transmission and reception would be affected, because the signal degrades over length.

Question # 15
What common software problems can lead to network defects?
Software related problems can be any or a combination of the following:

*    Client server problems
*    Application conflicts
*    Error in configuration
*    Protocol mismatch
*    Security issues
*    User policy and rights issues

Question # 16
Tell me which protocol can be applied when you want to transfer files between different platforms, such between UNIX systems and Windows servers?
Use FTP (File Transfer Protocol) for file transfers between such different servers. This is possible because FTP is platform independent.

Question # 17
Explain the use of a default gateway?
Default gateways provide means for the local networks to connect to the external network. The default gateway for connecting to the external network is usually the address of the external router port.

Question # 18
Define the proper termination rate for UTP cables?
The proper termination for unshielded twisted pair network cable is 100 ohms.

Question # 19
Explain netstat?
Netstat is a command line utility program. It provides useful information about the current TCP/IP settings of a connection.

Question # 20
What is ping?
Ping is a utility program that allows you to check connectivity between network devices on the network. You can ping a device by using its IP address or device name, such as a computer name.

Question # 21
Define peer to peer?
Peer to peer are networks that does not reply on a server. All PCs on this network act as individual workstations.

Question # 22
Tell me what advantages does fiber optics have over other media?
One major advantage of fiber optics is that is it less susceptible to electrical interference. It also supports higher bandwidth, meaning more data can be transmitted and received. Signal degrading is also very minimal over long distances.

Question # 23
Can you please explain the difference between hub and a switch?
A hub acts as a multi-port repeater. However, as more and more devices connect to it, it would not be able to efficiently manage the volume of traffic that passes through it. A switch provides a better alternative that can improve the performance especially when high traffic volume is expected across all ports.

Question # 24
Explain DNS?

DNS is Domain Name System. The main function of this network service is to provide host names to TCP/IP address resolution.

Question # 25
List the different network protocols that are supported by Windows RRAS services?
There are three main network protocols supported: NetBEUI, TCP/IP, and IPX.

Question # 26
How maximum networks and hosts are in a class A, B and C network?
1)    For Class A, there are 126 possible networks and 16,777,214 hosts
2)    For Class B, there are 16,384 possible networks and 65,534 hosts
3)    For Class C, there are 2,097,152 possible networks and 254 hosts

Question # 27
What is the standard color sequence of a straight-through cable?
Orange/white, orange, green/white, blue, blue/white, green, brown/white, brown.

Question # 28
Tell me what protocols fall under the application layer of the TCP/IP stack?
Following are the protocols under TCP/IP Application layer: FTP, TFTP, Telnet and SMTP.

Question # 29
Is it possible to connect two computers for file sharing without using a hub or router?
Yes, you can connect two computers together using only one cable. A crossover type cable can be use in this scenario. In this setup, the data transmit pin of one cable is connected to the data receive pin of the other cable, and vice versa.

Question # 30
Define ipconfig?
Ipconfig is a utility program that is commonly used to identify the addresses information of a computer on a network. It can show the physical address as well as the IP address.

Question # 31
Can you please explain the difference between straight-through and crossover cable?
A straight-through cable is used to connect computers to a switch, hub or router. A crossover cable is used to connect two similar devices together, such as a PC to PC or Hub to hub.

Question # 32
Explain client/server?
Client/server is a type of network wherein one or more computers act as servers. Servers provide a centralized repository of resources such as printers and files. Clients refers to workstation that access the server.

Question # 33
What is networking?

Networking refers to the inter connection between computers and peripherals for data communication. Networking can be done using wired cabling or through wireless link.

Question # 34
Suppose when you move the NIC cards from one PC to another PC, does the MAC address gets transferred as well?
Yes, that's because MAC addresses are hard-wired into the NIC circuitry, not the PC. This also means that a PC can have a different MAC address when the NIC card was replace by another one.

Question # 35
What is clustering support?
Clustering support refers to the ability of a network operating system to connect multiple servers in a fault-tolerant group. The main purpose of this is the in the event that one server fails, all processing will continue on with the next server in the cluster.

Question # 36
Suppose if a network which contains two servers and twenty workstations, where is the best place to install an Anti-virus program?
An anti-virus program must be installed on all servers and workstations to ensure protection. That's because individual users can access any workstation and introduce a computer virus when plugging in their removable hard drives or flash drives.

Question # 37
What is Ethernet?
Ethernet is one of the popular networking technologies used these days. It was developed during the early 1970s and is based on specifications as stated in the IEEE. Ethernet is used in local area networks.

Question # 38
Give some drawbacks of implementing a ring topology?
In case one workstation on the network suffers a malfunction, it can bring down the entire network. Another drawback is that when there are adjustments and reconfiguration's needed to be performed on a particular part of the network, the entire network has to be temporarily brought down as well.

Question # 39
Can you please explain the difference between CSMA/CD and CSMA/CA?
CSMA/CD, or Collision Detect, retransmits data frames whenever a collision occurred. CSMA/CA, or Collision Avoidance, will first broadcast intent to send prior to data transmission.

Question # 40
What is SMTP?
SMTP is short for Simple Mail Transfer Protocol. This protocol deals with all Internal mail, and provides the necessary mail delivery services on the TCP/IP protocol stack.

Question # 41
Define multicast routing?
Multicast routing is a targeted form of broadcasting that sends message to a selected group of user, instead of sending it to all users on a subnet.

Question # 42
Explain the importance of encryption on a network?

Encryption is the process of translating information into a code that is unreadable by the user. It is then translated back or decrypted back to its normal readable format using a secret key or password. Encryption help ensure that information that is intercepted halfway would remain unreadable because the user has to have the correct password or key for it.

Question # 43
How are IP addresses arranged and displayed?
IP addresses are displayed as a series of four decimal numbers that are separated by period or dots. Another term for this arrangement is the dotted decimal format.  An example is

Question # 44
Explain the importance of authentication?
Authentication is the process of verifying a user's credentials before he can log into the network. It is normally performed using a username and password. This provides a secure means of limiting the access from unwanted intruders on the network.

Question # 45
What is tunnel mode?
This is a mode of data exchange wherein two communicating computers do not use IPSec themselves. Instead, the gateway that is connecting their LANs to the  transit network creates a virtual tunnel that uses the IPSec protocol to secure all communication that passes through it.

Windows Administrator Interview Questions II

Question # 35
How to cancel a print job?
To cancel a print job:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Printers and Faxes. The Printers and Faxes control panel will appear.
*    Double-click the printer to which you sent the print jobs. The Printer window will open.
*    Click the job you want to stop. If you want to stop more than one job, hold down the Control key while you click the additional jobs.
*    Click Document, which is located on the menu bar.
*    Click Cancel.

Question # 36
How to restart print jobs which temporarily stopped?
To restart a print job you temporarily stopped:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A sub-menu will appear.
*    Click Printers and Faxes. The Printers and Faxes control panel will appear.
*    Double-click the printer to which you sent the print job. The Printer window will open.
*    Click the documents you paused. If more than one document has been paused, hold down the Ctrl key as you click the additional documents.
*    Click Document, which is located on the menu bar.
*    Click Pause. The check-mark next to Pause should disappear.

Question # 37
How to temporarily stop selected jobs from printing?
To temporarily stop selected jobs from printing:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Printers and Faxes. The Printers and Faxes control panel will appear.
*    Double-click the printer to which you sent the print job. The Printer window will open.
*    Click the document you want to pause. If you want to pause more than one document, hold down the Control key as you select the additional documents.
*    Click Document, which is located on the menu bar.
*    Click Pause. A check-mark should appear next to Pause.

Question # 38
Suppose if temporarily stopped all of the print jobs and now I want to restart them. How do I do that?
To restart a print queue that has been stopped:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A sub-menu will appear.
*    Click Printers and Faxes. The Printer control panel will appear.
*    Double-click the printer to which you sent the print job. The Printer window will open.
*    Click Printer, which is located on the menu bar. A drop-down menu will appear.
*    Click Pause Printing. The check-mark next to Pause Printing should disappear.

Question # 39
How to temporarily stop all jobs from printing?
To temporarily stop all jobs from printing:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A sub-menu will appear.
*    Click Printers. The Printer control panel will appear.
*    Double-click the printer to which you sent the print jobs. The Printer window will open.
*    Click Printer, which is located on the menu bar. A drop-down menu will appear.
*    Click Pause Printing. A check-mark should appear next to Pause Printing.

Question # 40
How to create a desktop shortcut?
To create a shortcut to an item located on the Start menu:

*    Click Start. The Start menu will appear.
*    Locate the item to which you want to create a shortcut. If the item is located on a sub-menu, go to the sub-menu.
*    Click and drag the item to your desktop.

Question # 41
What is desktop shortcut?
A desktop shortcut, usually represented by an icon, is a small file that points to a program, folder, document, or Internet location. Clicking on a shortcut icon takes  you directly to the object to which the shortcut points. Shortcut icons contain a small arrow in their lower left corner. Shortcuts are merely pointers deleting a shortcut will not delete the item to which the shortcut points.

Question # 42
How to create a shortcut to items visible in Windows Explorer?
*    Open Windows Explorer.
*    Minimize the Windows Explorer window.
*    Locate in Windows Explorer the item to which you want to create a shortcut.
*    Hold down the right mouse button and drag the item onto the desktop.
*    Release the right mouse button. A context menu will appear.
*    Click Create Shortcuts Here.

Question # 43
How to turn a Web link into a desktop shortcut?
To turn a Web link into a desktop shortcut, click the link in your browser window (usually underlined text) and drag it to the desktop. An icon will appear on your desktop. When you click the icon, your browser will open and you will go directly to the Web page.

Question # 44
How to delete a desktop shortcut?
To delete a shortcut:
*    Click the shortcut.
*    Press the Delete key.
*    Click Yes.

Question # 45
How to rename a desktop shortcut?
To rename a shortcut:
*    Right-click the shortcut.
*    Click Rename.
*    Type the new name.

Question # 46
How to change the icon associated with an object?
To change the icon associated with an object:
*    Right-click the icon. The context menu will appear.
*    Click Properties.
*    Click the Change Icon button.
*    Click the icon of your choice.
*    Click OK.

Question # 47
How does desktop shortcut wizard work?
*    Right-click the desktop. The context menu will appear.
*    Click New. A sub-menu will appear.
*    Click Shortcut. The Create Shortcut dialog box will appear.

*    Type in the location and name of the item to which you want to create a shortcut. Alternatively, browse to find the item.
*    Click Next. A dialog box will appear.
*    Accept the default name or type in a new name.
*    Click Finish.

Question # 48
What is the mean of image to appear on center screen?
Place the image in the center of the screen.

Question # 49
What is the mean of image to appear on Tile screen?
Have the image display as tiles across and down the screen.

Question # 50
What is the mean of image to appear on Stretch screen?
Stretch the image so the image covers the entire screen.

Question # 51
What is font?
A font is a set of characters represented in a single typeface. Each character within a font is created by using the same basic style.

Question # 52
What is font size?
Fonts are measured in points. There are 72 points to an inch. The number of points assigned to a font is based on the distance from the top to the bottom of its longest character.

Question # 53
How to install a new font?
To install a new font:
*    Click the Start button.
*    Highlight Settings.
*    Click Control Panel.
*    Click Fonts. The Fonts window will open.
*    Click File, which is located on the menu bar.
*    Click Install New Font.
*    Specify the drive and folder where the font you want to install is currently located.
*    Select the font you want to install from the fonts listed in the List of Fonts box.
*    Select Copy Fonts to Fonts Folder (this will put a copy of the font you are installing in the Fonts folder).
*    Click OK.

Question # 54
What is the Character Map?
The Character Map displays the characters available in a selected font. To view the Character Map dialog box:
*    Click the Start button.
*    Highlight Programs.
*    Highlight Accessories.
*    Highlight System Tools.
*    Click Character Map.

Question # 55

What is wallpaper?
Wallpaper is the background that displays on your desktop.

Question # 56
How to change wallpaper?
To change your wallpaper:
*    Right-click your desktop.
*    Highlight Properties.
*    Click the Desktop tab.
*    Select the wallpaper you want from the list that appears in the Background box.

Question # 57
How Windows XP organize files and folders on drives?
Windows XP organizes folders and files in a hierarchical system. The drive is the highest level of the hierarchy. You can put all of your files on the drive without creating any folders, but that is like putting all of your papers in a file cabinet without organizing them into folders. It works fine if you have only a few files, but as the number of files increases, there comes a point at which things become very difficult to find. So you create folders and put related material together in folders.

Question # 58
How to create a new folder when in Windows Explorer?
To create a new folder:
*    In the left pane, click the drive or folder in which you want to create the new folder.
*    Click any free area in the right pane. A context menu will appear.
*    Highlight New.
*    Click Folder.
*    Type a name for the folder.

Question # 59
What are folders?
Folders are used to organize the data stored on your drives. The files that make up a program are stored together in their own set of folders. You will want to organize the files you create in folders. You will want to store files of a like kind in a single folder.

Question # 60
Explain the Windows Explorer window?
Windows XP separates the window into two panes. If you click an object in the left pane, the contents of the object display in the right pane. Click Desktop and the contents of the Desktop folder display on the right. Click My Computer and your computer resources display on the right. To see the contents of a drive, click the drive. To see the contents of a folder, click the icon for the folder in the left pane.

Question # 61
How to change the Windows Explorer views?
To change the view:
*    Right-click any free area in the right pane. A context menu will appear.
*    Highlight View.
*    Select the view you want from the drop-down menu.

Question # 62
Explain Windows Explorer views?
Yes. Views control how Windows Explorer displays information in the right pane. Windows Explorer provides you with the following choices: Thumbnails, Tiles, Icons, List, and Details.
*    Thumbnails view displays images. These images represent the contents of folders and files. For example, if a folder contains pictures, up to four of the pictures in the folder will be displayed on the folder icon.

*    Tiles view and Icons view display icons to represent drives, folders, and the contents of folders. The icons displayed when you choose Tiles view are larger than the icons that display when you choose Icon view.
*    List view displays all of the files and folders without supplying the size, type, or date modified.
*    Details view displays the size, type, and date modified.

Question # 63
How to cut a file or folder?
To cut a file or folder:
*    Right-click the file or folder you want to cut. A context menu will appear.
*    Click Cut. The file or folder should now be on the Clipboard. Note:
Cutting differs from deleting. When you cut a file, the file is placed on the Clipboard. When you delete a file, the file is sent to the Recycle Bin.

Question # 64
How to delete a file or folder?
To delete a file or folder:
*    Right-click the file or folder you want to delete. A context menu will appear.
*    Click Delete. Windows Explorer will ask, "Are sure you want to send this object to the recycle bin?"
*    Click Yes.

Question # 65
How to paste a file or folder?
To paste a file or folder:
*    After cutting or copying the file, right-click the object or right-click in the right pane of the folder to which you want to paste. A context menu will appear.
*    Click Paste.

Question # 66
How to copy a file or folder?
To copy a file or folder:
*    Right-click the file or folder you want to copy. A context menu will appear.
*    Click Copy. The file or folder should now be on the Clipboard.

Question # 67
How to rename a file or folder?
To rename a file or folder:
*    Right-click the file or folder. A context menu will appear.
*    Click Rename.
*    Type the new name.

Question # 68
What is screen saver?
Computer monitors display images by firing electron beams at a phosphor-coated screen. If the same image stays on the screen too long, there is a danger that the image will leave a permanent imprint on the screen. Screen savers help prevent this by providing a constantly changing image.

Question # 69
How to select a screen saver?
To select a screen saver:
*    Right-click anywhere on the Windows desktop. A context menu will appear.
*    Choose Properties. The Display Properties dialog box will appear.
*    Click the Screen Saver tab.
*    The Screen Saver field provides the list of available screen savers. Select the screen saver you want from the list.
*    Click Preview to preview your screen saver.

*    Click Esc to return to the Display Properties dialog box.
*    In the Wait field, set the number of minutes of inactivity before the screen saver starts.
*    Click OK.

Question # 70
Where are games?
Several games are included with Windows XP. To access the games:
*    Click the Start button, which is located in the lower left corner of the screen. The Start menu will appear.
*    Highlight Programs. A submenu will appear.
*    Highlight Games. Another submenu will appear.
*    Click the game you want to play.

Question # 71
What are drives?
Drives are used to store data. Almost all computers come with at least two drives: a hard drive (which is used to store large volumes of data) and a CD drive(which stores smaller volumes of data that can be easily transported from one computer to another). The hard drive is typically designated the C: drive and the CD drive is typically designated the D: drive. If you have an additional floppy drive, it is typically designated the A: drive. If your hard drive is partitioned or if you have additional drives, the letters E:, F:, G: and so on are assigned.

DBA Interview Questions

DBA Interview Questions with Answers

Can one switch to another database user without a password?
Users normally use the "CONNECT" statement to connect from one database user to another. However, DBAs can switch from one user to another without a password. Of course it is not advisable to bridge Oracle's security, but look at this example:
SQL> CONNECT / as sysdba
SQL> SELECT password FROM dba_users WHERE  username='SCOTT';
SQL> CONNECT scott/anything
OK, we're in. Let's quickly change the password back before anybody notices.
User altered.
How do you delete duplicate rows in a table?
There is a several method to delete duplicate row from the table:
delete from SHAAN t1
where  exists (select 'x' from SHAAN t2
and t2.rowid      > t1.rowid);
WHERE  rowid IN
delete from SHAAN where rowid not in
( select min(rowid)
from SHAAN group by EMPLOYEE_ID);
delete from SHAAN
where rowid not in ( select min(rowid)
from SHAAN group by EMPLOYEE_ID);
SQL> create table table_name2 as select distinct * from table_name1;
SQL> drop table table_name1;
SQL> rename table_name2 to table_name1;
What is Automatic Management of Segment Space setting?
Automatic Segment Space Management (ASSM) introduced in Oracle9i is an easier way of managing space in a segment using bitmaps. It eliminates the DBA from setting the parameters pctused, freelists, and freelist groups.
ASSM can be specified only with the locally managed tablespaces (LMT). The CREATE TABLESPACE statement has a new clause SEGMENT SPACE MANAGEMENT. Oracle uses bitmaps to manage the free space. A bitmap, in this case, is a map that describes the status of each data block within a segment with respect to the amount of space in the block available for inserting rows. As more or less space becomes available in a data block, its new state is reflected in the bitmap.
CREATE TABLESPACE myts DATAFILE '/oradata/mysid/myts01.dbf' SIZE 100M

What is COMPRESS and CONSISTENT setting in EXPORT utility?
If COMPRESS=Y, the INITIAL storage parameter is set to the total size of all extents allocated for the object. The change takes effect only when the object is imported.
Setting CONSISTENT=Y exports all tables and references in a consistent state. This slows the export, as rollback space is used. If CONSISTENT=N and a record is modified during the export, the data will become inconsistent.
What is the difference between Direct Path and Convention Path loading?
When you use SQL loader by default it use conventional path to load data. This method competes equally with all other oracle processes for buffer resources. This can slow the load. A direct path load eliminates much of the Oracle database overhead by formatting Oracle data blocks and writing the data blocks directly to the database files. If load speed is most important to you, you should use direct path load because it is faster.
What is an Index Organized Table?
An index-organized table (IOT) is a type of table that stores data in a B*Tree index structure. Normal relational tables, called heap-organized tables, store rows in any order (unsorted).
What are a Global Index and Local Index?
When you create a partitioned table, you should create an index on the table. The index may be partitioned according to the same range values that were used to partition the table. Local keyword in the index partition tells oracle to create a separate index for each partition of the table. TheGlobal clause in create index command allows you to create a non-partitioned index or to specify ranges for the index values that are different from the ranges for the table partitions. Local indexes may be easier to manage than global indexes however, global indexes may perform uniqueness checks faster than local (portioned) indexes perform them.
What is difference between Multithreaded/Shared Server and Dedicated Server?
Oracle Database creates server processes to handle the requests of user processes connected to an instance.dedicated server process, which services only one user processshared server process, which can service multiple user processes
Your database is always enabled to allow dedicated server processes, but you must specifically configure and enable shared server by setting one or more initialization parameters.
Can you import objects from Oracle ver. 7.3 to 9i?
We can not import from lower version export to higher version in fact. But not sure may be now concept is changed.
How do you move tables from one tablespace to another tablespace?
Method 1:
Export the table, drop the table, create the table definition in the new tablespace, and then import the data (imp ignore=y).
Method 2:
Create a new table in the new tablespace with the "CREATE TABLE x AS SELECT * from y" command:
CREATE TABLE temp_name TABLESPACE new_tablespace AS SELECT * FROM real_table;
Then drop the original table and rename the temporary table as the original:
DROP TABLE real_table;
RENAME temp_name TO real_table;
Note: After step #1 or #2 is done, be sure to recompile any procedures that may have been
invalidated by dropping the table. Prefer method #1, but #2 is easier if there are no indexes, constraints, or triggers. If there are, you must manually recreate them.
Method 3:
If you are using Oracle 8i or above then simply use:
SQL>Alter table table_name move tablespace tablespace_name;

How do see how much space is used and free in a tablespace?
Can view be the based on other view?
Yes, the view can be created from other view by directing a select query to use the other view data.
What happens, if you not specify Dictionary option with the start option in case of LogMinor concept?
It is recommended that you specify a dictionary option. If you do not, LogMiner cannot translate internal object identifiers and datatypes to object names and external data formats. Therefore, it would return internal object IDs and present data as hex bytes. Additionally, the MINE_VALUE andCOLUMN_PRESENT functions cannot be used without a dictionary.

What is the Benefit and draw back of Continuous Mining?

The continuous mining option is useful if you are mining in the same instance that is generating the redo logs. When you plan to use the continuous mining option, you only need to specify one archived redo log before starting LogMiner. Then, when you start LogMiner specify theDBMS_LOGMNR.CONTINUOUS_MINE option, which directs LogMiner to automatically add and mine subsequent archived redo logs and also the online catalog.
Continuous Mining is not available in Real Application Cluster.
What is LogMiner and its Benefit?
LogMiner is a recovery utility. You can use it to recover the data from oracle redo log and archive log file. The Oracle LogMiner utility enables you to query redo logs through a SQL interface. Redo logs contain information about the history of activity on a database.
Benefit of LogMiner?
1.  Pinpointing when a logical corruption to a database; suppose when a row is accidentally deleted then logMiner helps to recover the database exact time based and changed based recovery.
2.  Perform table specific undo operation to return the table to its original state. LogMiner reconstruct the SQL statement in reverse order from which they are executed.
3.  It helps in performance tuning and capacity planning. You can determine which table gets the most update and insert. That information provides a historical perspective on disk access statistics, which can be used for tuning purpose.
4.  Performing post auditing; LogMiner is used to track any DML and DDL performed on database in the order they were executed.
What is Oracle DataGuard?
Oracle DataGuard is a tools that provides data protection and ensures disaster recovery for enterprise data. It provides comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruption. Dataguard maintains these standsby databases as transitionally consistent copies of the production database. Then, if the production database becomes failure Data Guard can switch any standby database to the production role, minimizing the downtime associated with the outage. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.
What is Standby Databases
A standby database is a transitionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to9 standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo 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:
Difference between Physical standby Logical standby databases
Provides a physically identical copy of the primary database on a block-for-block basis. The database schema, including indexes, is the same. A physical standby database is kept synchronized with the primary database, though Redo Apply, which recovers the redo data, received from the primary database and applies the redo to the physical standby 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. The logical standby database is kept synchronized with the primary database though SQL Apply, which transforms the data in the redo received from the primary database into SQL statements and then executing the SQL statements on the standby database.
If you are going to setup standby database what will be your Choice Logical or Physical?
We need to keep the physical standby database in “recovery mode” in order to apply the received archive logs from the primary database. We can open “physical stand by database to “read only” and make it available to the applications users (Only select is allowed during this period). Once the database is opened in “Read only” mode then we can not apply redo logs received from primary database.
We do not see such issues with logical standby database. We can open up the database in normal mode and make it available to the users. At the same time, we can apply archived logs received from primary database.
If the primary database needed to support pretty large user community for the OLTP system and pretty large “Reporting Group” then better to uselogical standby as primary database instead of physical database.
What are the requirements needed before preparing standby database?
·   OS Architecture of primary database secondary database should be same.
·   The version of secondary database must be the same as primary database.
·   The Primary database must run in Archivelog mode.
·   Require the same hardware architecture on the primary and all standby site.
·   Does not require the same OS version and release on the primary and secondary site.
·   Each Primary and secondary database must have its own database.
What are “Failover” and “Switchover” in case of dataguard?
Failover is the operation of bringing one of the standby databases online as the new primary database when failure occurs on the primary database and there is no possibility of recover primary database in a timely manner. The switchover is a situation to handle planned maintenance on the primary database. The main difference between switchover operation and failover operation is that switchover is performed when primary database is still available or it does not require a flash back or re-installation of the original primary database. This allows the original primary database to the role of standby database almost immediately. As a result schedule maintenance can performed more easily and frequently.
When you use WHERE clause and when you use HAVING clause?
HAVING clause is used when you want to specify a condition for a group function and it is written after GROUP BY clause The WHERE clause is used when you want to specify a condition for columns, single row functions except group functions and it is written before GROUP BY clause if it is used.
What is a cursor and difference between an implicit & an explicit cursor?
A cursor is a PL/SQL block used to fetch more than one row in a Pl/SQl block. PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including quries that return only one row. However, queries that return more than one row you must declare an explicit cursor or use a cursor FOR loop.
Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT statement via the CURSOR...IS statement. An implicit cursor is used for all SQL statements Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements An implicit cursor is used to process INSERT, UPDATE, DELETE and single row SELECT. .INTO statements.

Explain the difference between a data block, an extent and a segment.A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.
A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?Disable the foreign key constraint to the parent, drop the table, re-create the table, and enable the foreign key constraint.
How to Unregister database from Rman catalog
First we start up RMAN with a connection to the catalog and the target, making a note of the DBID in the banner:
C:\>rman catalog=rman/rman@shaan target=HRMS/password@orcl3
connected to target database: W2K1 (DBID=691421794)
connected to recovery catalog database
Note the DBID from here. Next we list and delete any backupset recorded in the repository:
Next we connect to the RMAN catalog owner using SQL*Plus and issue the following statement:
SQL> CONNECT rman/rman@shaan
SQL> SELECT db_key, db_id  FROM   db
                WHERE  db_id = 1487421514;
                DB_KEY                DB_ID
----------                   ----------
                1                              691421794
The resulting key and id can then be used to unregister the database:
SQL> EXECUTE dbms_rcvcat.unregisterdatabase(1, 691421794);
PL/SQL procedure successfully completed.

DBA Interview Questions 2

DBA Interview Questions With Answers

What are four common errors found in an alert .log?
If we are getting any issue regarding database while performing any activity we should check alert log file in dump destination.. The four common error we find in alert.log are:
Deadlock Errors (ORA-00060), Oracle Internal errors, Backup and recovery errors, Snapshot too old error (O1555)
What is PCT Free/PCT Used/PCT increase parameter in segment? What is growth factor?
PCT-FREE is a block storage it uses to mention how much space should be left in database block for future updates (updating the records eg. previously name Smith after that we will update the name as Smith Taylor). If mention PCTFREE as 10, oracle will adding the new rows to block up to 90% it allows 10% for future updates.
If the PCT used was set to 60 this means if the data inside the block is 60 it is FULL and if the data inside the block is 59 it is Empty.
This is the parameter which specify in percent that a block can only used for insert or come in the free list(list of blocks in segment ready for insert operation) when used space in a block is less than PCTUSED.
Suppose value of pctused is 40 and pctfree is 20 then data can be inserted till 80 of the block directly. And suppose the used space is 60 and some one has perform a delete operation in a row in the same block which brings the used space to 50 .Now one cannot insert any record in the same block unless the used space comes down below 40 i.e. pctused.

What is dump destination? What are bdump, cdump and udump?
The dump destination is the location where the trace files are located for all the Oracle process.
bdump-->Background processes + alert_SID.log file location
cdump--> Core Processes dump, udump--> User Processes dump, adump--> for ASM processes
These destinations contains useful information related to process failures.

UDUMP is specifying the user dump directory where all user error logs (trace files) will be placed.
BDUMP is specifying the background dump directory where all database error logs (trace files) will be placed.
CDUMP is specifying the core dump directory where all OS error logs (core dump files) will be placed.
Default location is (ORACLE_BASE/admin/<SID>) 
SQL>show parameters dump_dest;

It'll show you all the dump directories wherever it is currently located. You can change your parameters in init.ora by creating spfile from pfile.
What will you do if in any condition you do not know how to troubleshoot the error at all and there are no seniors or your co-workers around?

We need to find where in the compilation the error is occurring. We have to divide the code and check for correctness of the code part-by-part. This is called debugging. Keep checking the code until you find the code which is wrong.
Search forums for similar error codes or symptoms and make a plan then submit it to your supervising DBA if you are not authorized to carry it out yourself.

I am getting error "No Communication channel" after changing the domain name? What is the solution?
Here Question is not clear about Where the Oracle database is residing. If the Oracle Database is resides on your local machine then the domain name must be updated in the tnsnames.ora file. Change this file in ../Admin folder contained one. If you are accessing remote Database then there are no changes required to your tnsnames.ora file only check with tnsping with the database service name. Change the domain name in the sqlnet.ora file in NAMES.DEFAULT_DOMAIN parameter
You have taken import of a table in a database. You have got the Integrity constraint violation error. How you are going to resolve it.
If u wants to import the table just says constraints=n the movement table got imported then u create constraint on that tables.
What is the most important action a DBA must perform after changing the database from NOARCHIVELOG TO ARCHIVELOG?
First of all take an offline backup of whole database (including the (datafile controlfile and redolog files). It is obvious that archive log process should be started by: 
SQL>alter system Archivelog start;

Otherwise the database halts if unable to rotate redo logs
Show one instance when you encountered an error in alert log and you overcome that error. What actions you took to overcome that error.
Oracle writes error in alert log file. Depending upon the error corrective action needs to be taken.
1) Deadlock Error: Take the trace file in user dump destination and analysis it for the error.
2) ORA-01555 Snapshot error: Check the query try to fine tune and check the undo size.
3) Unable to extent segment: Check the tablespace size and if require add space in the tablespace by 'alter database datafile .... resize' or alter tablespace add datafile command.
What is Ora-1555 Snapshot too Old error? Explain in detail?
Oracle Rollback Segments (Undo more recently) hold a copy of data before it was modified and they work in a round-robin fashion. Writing and then eventually overwriting the entries as soon as the changes are committed.
They are needed to provide read consistency (a consistent set of data at a point in time) or to allow a process to abandon or rollback the changes or for database recovery.
Here’s a typical scenario:-
User A opens a query to fetch every row from a billion row table. If User B updates and commits the last row of the billion row table a Rollback entry will be created so User A can see the data as it was before the update.
Other users are busily updating rows in the database and this in turn generates rollback – which may eventually cause the entry needed for User A to be overwritten (after all User B did commit the change – so it’s OK to overwrite the rollback segment). Maybe 15 minutes later the query is still running and User A finally fetches the last row of the billion row table – but the rollback entry is gone. He gets ORA-01555: Snapshot too old rollback segment too small
I have applied the following commands: Now what will happen, will the database will give an error / it will work?
Shutdown abort;
Definitely database will be start without error but all uncommitted data will be lost such as killed all sessions, killed all transactions, and didn't write from the buffers because shutdown abort directly shutdown instance without committing.

There is four modes to shutdown the database:
1) Shutdown immediate, 2) Shutdown normal, 3) Shutdown transactional, 4) Shutdown aborts
When the database is shutdown by first 3 methods checkpoint takes place but when is shutdown by abort option it doesn't enforces checkpoints, it simply shutdowns without waiting any users to disconnect.

What is mutated trigger? In single user mode we got mutated error, as a DBA how you will resolve it?
Mutated error will occur when same table access more than once in one state. If you are using before in trigger block then replace it with after.
Explain Dual table. Is any data internally stored in dual Table. Lot of users is accessing select sysdate from dual and they getting some millisecond differences. If we execute SELECT SYSDATE FROM EMP; what error will we get. Why?

Dual is a system owned table created during database creation. Dual table consist of a single column and a single row with value x. We will not get any error if we execute select sysdate from scott.emp instead sysdate will be treated as a pseudo column and displays the value for all the rows retrieved. For Example if there is 12 rows in emp table it will give result of date in 12 rows.
As an Oracle DBA what are the entire UNIX file you should be familiar with?
To check the process use:  ps -ef |grep pmon or ps -ef
To check the alert log file:  Tail -f alert.log 
To check the cpu usage;    Top vmstat 2 5

What is a Database instance?
A database instance also known as server is a set of memory structures and background processes that access a set of database files. It is possible for a single database to be accessed by multiple instances (this is oracle parallel server option). 
What are the Requirements of simple Database?
A simple database consists of:
One or more data files, One or more control files, Two or more redo log files, Multiple users/schemas, One or more rollback segments, One or more Tablespaces, Data dictionary tables, User objects (table, indexes, views etc.)
The server (Instance) that access the database consists of:
SGA  (Database  buffer,  Dictionary  Cache  Buffers, Redo log buffers, Shared SQL pool), SMON (System Monitor),PMON (Process Monitor), LGWR (Log  Write), DBWR (Data Base Write), ARCH (ARCHiver), CKPT  (Check Point), RECO, Dispatcher, User Process with associated PGS
Which process writes data from data files to database buffer cache?
The Background process DBWR rights data from datafile to DB cache.
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) clean the UDUMP, BDUMP, scripts etc, 7) Cleanup the listener.ora and the tnsnames.ora. Make sure that the oratab entry is also removed. 

Otherwise, go to DBCA and click on delete database.
In Oracle 10g there is a new command to drop an entire database.
Startup restrict mount;
drop database <instance_name>;

In fact DBA should never drop a database via OS level commands rather use GUI utility DBCA to drop the database
How can be determining the size of the log files.
Select sum(bytes)/1024/1024 "size_in_MB" from v$log;
What is difference between Logical Standby Database and Physical Standby database?
A physical or logical standby database is a database replica created from a backup of a primary database. A physical standby database is physically identical to the primary database on a block-for-block basis.  It's maintained in managed recovery mode to remain current and can be set to read only; archive logs are copied and applied.
A logical standby database is logically identical to the primary database.  It is updated using SQL statements
How do you find whether the instance was started with pfile or spfile
1) SELECT name, value FROM v$parameter WHERE name = 'spfile';
This query will return NULL if you are using PFILE

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:
SQL> SELECT DECODE(value, NULL, 'PFILE', 'SPFILE') "Init File Type"

           FROM sys.v_$parameter WHERE name = 'spfile';
What is full backup?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute oracle database and the parameter.If you are using the Rman for backup then in Rman full backup means Incremental backup on 0 level.
While taking hot backup (begin end backup) what will happens back end?
When we r taking hot backup (begin backup - end backup) the datafile header associated with the datafiles in the corresponding Tablespace is frozen. So Oracle will stop updating the datafile header but will continue to write data into datafiles. In hot backup oracle will generate more redos this is because oracle will write out complete changed blocks to the redo log files.
Which is the best option used to move database from one server to another serve on same network and Why?
Import – Export, Backup-Restore, Detach-Attach

Import-Export is the best option used to move database from one server to another serve on same network. It reduces the network traffic.Import/Export works well if you’re dealing with very small databases. If we have few million rows its takes minutes to copy when compared to seconds using backup and restore.

What is Different Type of RMAN Backup?
Full backup: During a Full backup (Level 0) all of the block ever used in datafile are backed up. The only difference between a level 0 incremental backup and a full backup is that a full backup is never included in an incremental strategy.
Comulative Backup: During a cumulative (Level 0) the entire block used since last full backup are backed up.
Differential Backup: During incremental backup only those blocks that have changed since last cumulative (Level 1) or full backup (Level 0) are backed up. Incremental backup are differential by default.
Give one method for transferring a table from one schema to another:
There are several possible methods: Export-Import, CREATE TABLE... AS SELECT or COPY.
What is the purpose of the IMPORT option IGNORE? What is its default setting?
The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is not specified the tables that already exist will be skipped. If it is specified, the error is ignored and the table’s data will be inserted. The default value is N.
What happens when the DEFAULT and TEMP tablespace clauses are left out from CREATE USER statements?
The user is assigned the SYSTEM tablespace as a default and temporary tablespace. This is bad because it causes user objects and temporary segments to be placed into the SYSTEM tablespace resulting in fragmentation and improper table placement (only data dictionary objects and the system rollback segment should be in SYSTEM).
What happens if the constraint name is left out of a constraint clause?
The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system generated number. This is bad since it makes tracking which table the constraint belongs to or what the constraint does harder.
What happens if a Tablespace clause is left off of a primary key constraint clause?
This result in the index that is automatically generated being placed in then USERS default tablespace. Since this will usually be the same tablespace as the table is being created in, this can cause serious performance problems.
What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause?
The index is created in the user’s default tablespace and all sizing information is lost. Oracle doesn’t store this information as a part of the constraint definition, but only as part of the index definition, when the constraint was disabled the index was dropped and the information is gone.
Using hot backup without being in archive log mode, can you recover in the event of a failure? Why or why not?
You can't recover the data because in archive log mode it take the backup of redo log files if it in Active mode, If it in inactive mode then it is not possible to take the backup of redolog files once the size is full, so in that case it is impossible to take hot backup
What causes the "snapshot too old" error? How can this be prevented or mitigated?
This is caused by large or long running transactions that have either wrapped onto their own rollback space or have had another transaction write on part of their rollback space. This can be prevented or mitigated by breaking the transaction into a set of smaller transactions or increasing the size of the rollback segments and their extents.
How can you tell if a database object is invalid?

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