Blogging World

PHP AJAX simple example

2009-12-11T14:15:00.002+05:30

Today I'll write simple AJAX (Asynchronous JavaScript And XML) program using PHP language.
In this example, you will be able to display user a Welcome Message without refreshing the webpage.
The webpage have one Name textbox and a command button. When user enter his name in textbox and press the Hola button, it will display 'Hola User!' message.

If the name textbox is left blank, it will display message 'Hola Guest!'.

Here is the home.html code.

<html>
<head>
<script type="text/javascript" src="simple.js"></script>
</head>
<body>
Name: <input type="text" id="txtName"/>
<input type="button" id="btnHola" value="Hola" onClick="HolaMe(txtName.value)"></input
<p><span id="txtMsg"></span></p>
</body>
</html>

This html file need simple.js javascript file to process your request asynchronously. The simple.js file looks like below

var xmlhttp;
function HolaMe(str)
{
if(str.length==0)
{
document.getElementById("txtMsg").innerHTML="Hola Guest!";
return;
}
xmlhttp=GetXmlHttpObject();
if(xmlhttp==null)
{
alert("Your browser don't support XMLHTTP!");
return;
}
var url="hola.php";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlhttp.onreadystatechange=showHolaMsg;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

function showHolaMsg()
{
if(xmlhttp.readyState==4)
{
document.getElementById("txtMsg").innerHTML=xmlhttp.responseText;
}
}

function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
{
// code for IE7+, Firefox, Chrome, Opera, Safari
return new XMLHttpRequest();
}
if (window.ActiveXObject)
{
// code for IE6, IE5
return new ActiveXObject("Microsoft.XMLHTTP");
}
return null;
}

This javascript check if the textbox is empty it displays 'Hola Guest!' message. Otherwise it sends the user name to hola.php file.

The hola.php file is very simple. It just echo the formatted response.

<?php
$q=$_GET["q"];
$response="Hola ".$q."!";
echo $response;
?>

Computer Networks Fundamentals

2009-05-11T08:11:00.002+05:30

Today we'll learn some computer networks fundamentals. You might have heard about following terms in day to day life, but this post will give you detail idea about them.

What is Protocol?

Protocol is an agreement between the communication parties about how communication is to proceed.

Connection-oriented service: The service first establish connection, uses the connection and then release the connection.

Connection-less service: Each message carries the full destination address and each one is routed independent of others.

OSI Reference Model/Open System Interconnect Model:

Physical Layer: transmitting raw bits over a communication channel.
Data Link Layer: break up input data (raw bits) into data frames (few hundress/thousand bytes) and transmit the frames sequentially. If service is reliable, receiver send Acknowledgment frame.
Network Layer: controls the operation of the subnet.
Transport Layer: accept data from above, split it into smaller units pass these to the network layer and ensure that all arrived correctly at the other end. Also determine what kind of service to provide to Session Layer ultimately to end user of the network.
Session Layer: allows user on different machines to establish sessions between them. Offers various services including dialog control (keeping track of whose turn it is to transmit), token management (preventing two parties attempting the same critical operation at the same time), synchronization (checkpointing long transmissions to allow them to continue from where they were after a crash).
Presentation Layer: unlike lower layers, which are concerned with moving bits around, this layer is concerned with the syntax and semantics of information transmitted. To allow computers with different data representations to communication, the data structures can be defined in abstract way.
Application Layer: contains a variety of protocols needed by user like HTTP (Hyper Text Transfer Protocol). Other application protocols are used for file transfer, email and network news.

TCP/IP Reference Model:

Host to network Layer: This is not defined by TCP/IP and it varies from host to host and n/w to n/w.
Internet Layer: is connectionless internetwork layer. Its job is to permit host to inject packets into any network and have them travel independently to the destination. They may arrive in different order and its job of higher layers to rearrange them. The internet layer define official packet format and protocol called IP (Internet Protocol). The job of Internet layer is to deliver IP packets to destination.
Transport Layer: allow peer entities to carry on a conversation. Two protocols are defined-
1. TCP (Transmission Control Protocol): reliable connection-oriented protocol allows a byte stream originating on one machine to be delivered on other machine. It fragment incoming byte stream into discrete messages and pass them on internet layer. At destination, TCP reassemble incoming messages. TCP also handle flow control to allow fast sender and slow receiver communication.
2. UDP (User Datagram Protocol): unreliable connection-less protocol. Used for once shot, client-server type request reply queries and application in which prompt delivery is more important than accurate delivery (e.g. speech and video transmission).
TCP/IP model does not have session or presentation layers.
Application Layer: Contains all higher level protocols like virtual terminal (TELNET), FTP, and email (SMPT). Virtual terminal allow user on one m/c to log onto distant m/c and work there. The FTP allows user to move data efficiently. SMTP is for email in which other protocols are added like Domain Name System (DNS) for mapping host names onto their network addresses, NNTP the protocol for moving USENET news articles around and HTTP the protocol for fetching pages on the World Wide Web and many more.

DNS(Domain Name System): DNS is used for mapping host names and e-mail destinations to IP addresses.
Working-To map name onto an IP address, an application program calls the resolver with name as parameter. The resolver then sends a UDP packet to a local DNS server which then looks up the name and returns the IP address to the resolver, which then returns it to the caller. The program then can establish a TCP connection or send UDP packets.

DHCP(Dynamic Host Configuration Protocol): allows both manual and automatic IP address assignment. The DHCP server need not be on same LAN as the requesting host. Since DHCP server may not be reachable by broadcasting, a DHCP relay agent is needed on each LAN.
To find its IP, newly booted system broadcasts a DHCP DISCOVER packet. The DHCP relay agent on its LAN intercepts all DHCP broadcasts and sends the packet as a unicast packet to the DHCP server possibly on a distant network. The only information the relay agent need is IP address of DHCP server.
Automatic IP assignment use a technique called leasing. Just before lease expires the host must ask DHCP for renewal otherwise host may no longer be able to use same IP. This helps to avoid permanent loss of IP, if host fail to return it to DHCP.

References: Some of the content is referred from the book Computer Networks by A. Tannenbaum

Enable OpenMP in Visual Studio

2009-04-25T23:55:00.006+05:30

To Enable OpenMP support in Visual Studio:

To use OpenMP, you must do the following

1. Include

2. Enable OpenMP compiler switch in Project Properties>>Configuration Properties>>C/C++>>Language>>OpenMP Support > Yes(/openmp)

3. That's all!

Applicable to: Visual Studio 2008

Sql Server 2005 on Windows 2008

2008-10-25T23:55:00.001+05:30

For those who face error 26 for SQL Server 2005 installed on Windows Server 2008

Named instances of SQL server connect to dynamic TCP/IP Ports instead of default 1433. SQL Server Browser which is listening on 1434 , respond to the client request and returns the TCP/IP port or named pipe associated with the requested SQL Server instance.

On Windows 2008 Server you need to configure your firewall for requests coming on UDP 1434
Check if Sql Server instance is running in SQL Server Configuration manager
Check if Sql Server Browser is running in SQL Server Configuration manager. (You can use netstat to make sure UDP 1434 is in use)
Check if firewall is allowing connections

To open Windows server 2008 firewall go to ServerManager/Configuration/Windows firewall

Changing the name of a SQL Server Host machine

2008-09-25T23:55:00.000+05:30

Overview
If you change the name of a machine with SQL Server installed, you need to do a few things in SQL Server after the host name change.
This blog applies to SQL Server 7.0, 2000, 2005 and 2008.

Note: If the SQL Server is installed in a cluster, you should reinstall.

Step 1 (all versions)
After starting SQL Server, you need to take care of the sysservers table in the master database. SQL Server stores the local machine name here and this will not match if you have renamed the machine in Windows. This is also easy to fix:

EXEC sp_dropserver ''
GO
EXEC sp_addserver '', 'local'
GO

You need to replace above with the old machine name and with the new machine name. If you have instance name, then the server names will be .
Get old name of server by executing-

EXEC sp_helpserver
GO

OR
SELECT * FROM sysservers

Step 3 (7.0 and 2000)
In this last step, you need to handle the sysjobs table in the msdb database. There is one row in sysjobs for each SQL Server agent job. In the column originating_server, you find the name of the server where the job was created. This is to support master and target server (MSX). If a job is created on a master server, you cannot modify the job definition on the targer server; all modifications has to be done on the master server.

So, if you changed the machine name, SQL Server will think that the job originated on a master server, and you will not be able to do anything with that job definition. You can handle this in two ways:

1. Rename the machine back to the old name, script the job definitions, delete the jobs, rename the machine to the new name again and use the script to re-create the jobs. See Error 14274 Occurs When You Update a SQL Agent Job After Renaming Windows Server for more information.

2. I find it easier to modify the sysjobs table directly. Note that this isn't supported and if you don't feel confident with doing below, don't; use above steps instead.

DECLARE @srv sysname
SET @srv = CAST(SERVERPROPERTY('ServerName') AS sysname)
UPDATE sysjobs SET originating_server = @srv

If this is a target server (you have jobs sent from a master server), you have to exclude them, so you don't convert those jobs into local jobs:

WHERE originating_server = ''

You need to replace above with the old machine name.

Restore master database - Sql Server 2005

2008-05-25T23:55:00.001+05:30

If you want to restore your master database then you need to follow those steps-
1. Disable all services of Sql server. One way to do this is- Open 'Sql Server Configuration Manager' then disable all services running under 'Sql Server 2005 services'.
2. Now run Sql server instance in single user mode by running
NET START "Sql Server (InstanceName)" /m
3. Now open the sqlcmd or Management studio and launch New Query window. (If you connect to instance and then try to connect to new query, it wont allow as you already connected to Instance. So one way is to disconnect to instance from Disconnect button in Management studio. Then click on New Query, it will ask for Username and Pwd)
4. Now restore your master database using
use master
Restore database master from disk = '...'
5. Now all changes in master after the backup you restore will be lost. So if you have created any users/logins you need to create then. If you have any databases created after that, you will not be able to find them under System databases. So you can Attach them from management studio from the Data file path of sql server.

Enable & Disable Hibernate on Windows Vista

2008-02-07T23:55:00.001+05:30

On Windows Vista, there is not option to enable or disable Hibernate. Here is the trick to do so…

To enable hibernation:

Click Start.

Type powercfg /hibernate on

Press Ctrl+Shift+Enter.

To disable hibernation:

Click Start.

Type powercfg /hibernate off

Press Ctrl+Shift+Enter.

SQL Server Backup & Recovery

2008-01-25T23:55:00.001+05:30

Backup

Full Backup: With this backup you are backing up the entire database and will be able to restore the entire database from just this backup. This backup will match the state of the database at the time the backup completes (except for uncommitted transactions which on restore of the backup will be rolled back). Generally this backup takes up the most time and uses up the most space out of all of the different types of backups.

Differential Backup: A differential backup will record all of the data that has changed since the last database backup (differential is the cumulative of all changes since the last full backup) you must have a database backup in place to use a starting point for your differential backup. Like database backups, differential backups will match the state of the database at the time that the backup is completed. Differential backups aren't like transaction log backups because they aren't incremental. When a differential backup occurs, it does not pay any regard to any differential backups that occurred before, it looks back only to the last database backup and records any data changed since that database backup.

Transaction log (Incremental) Backup: Transaction log backups record all transactions that have been recorded against the database since the last transaction log backup. You must have either a differential database backup or a database backup to use as a starting point for your transaction log backups. Unlike database and differential backups, transaction log backups will match the state of the database at the time that the backup is started. These backups use less space and time than database backups, and should be taken frequently to avoid loss of data. Your transaction logs should also be located on a separate disk if possible from your data files.

File Backup: File backups involve backing up individual files within a database. This can be the quickest way to restore, but it also has a lot of overhead associated with it. You must keep track of your file backups as well as use these file backups in conjunction with transaction log backups. Transaction log backups must be performed after a file backup is completed. You will restore your file backups first, and then all transaction log backups that occurred.

Both the differential and transaction log backups requires the Full backup to be restored first before they can be restored.

Permissions Required for Backup and Restore: Any logon that requires permissions to perform backup or restore operations should be provided membership in the following SQL Server roles.
Permissions required for performing backup-
Server Role : sysadmin
DB role : db_backupoperator, dbo_owner
Permissions required for performing restore -
Server role : sysadmin, dbcreator
DB role : db_owner

Creating a Backup Device using T-SQL:
Exec sp_addumpdevice 'device_type', 'logical_name', 'physical_name_or_location'
Exec sp_addumpdevie 'disk', 'Test Backup', 'D:\Backups\Test_Backup.bak'

To Check Transaction Log File being used:
DBCC SQLPERF(LOGSPACE)

Backup Database:
BACKUP DATABASE northwind
TO DISK = 'd:\backups\northwind\nwind.bak'

Full Backup:
BACKUP DATABASE [Inventory]
TO [InventoryBackup1], [InventoryBackup2], [InventoryBackup3]
WITH

FORMAT,
MEDIANAME = N'InventoryStripeSet',
MEDIADESCRIPTION = N'3 Devices = InventoryBackup1-3',
MEDIAPASSWORD = N'InventoryStripeSetPassword',
RETAINDAYS = 7,
NAME = N'InventoryBackup',
DESCRIPTION = N'Full Database Backup of Inventory',
PASSWORD = N'InventoryBackupFullDBPassword',
NOREWIND, STATS = 10

MediaName, MediaDescription- Every media should have name and description
MediaPassword- If a password is used on the backup, a media set password will need to be supplied for every restore.
Password-This password is for the individual backup, not the media set.
Name, Description-Every backup should have a name and a description.
INIT initializes backup devices only when they are in the correct structure.
RETAINDAYS set the backup retention period. The retention period is set as the number of days that must pass before the backup can be overwritten with INIT.
EXPIREDATE is the date when a backup can use INIT- to the same device- without error
All expiration options are discarded if FORMAT is used or if SKIP is used. If you use FORMAT, it implies the use of SKIP.

Differential Backup:
BACKUP DATABASE MyNwind
TO MyNwind_1 WITH DIFFERENTIAL
GO

BACKUP DATABASE [Inventory]
TO [InventoryBackup1], [InventoryBackup2], [InventoryBackup3]
WITH

DIFFERENTIAL, NOINIT,
MEDIAPASSWORD = N'InventoryStripeSetPassword',
NAME = N'InventoryDiffBackup',
DESCRIPTION = N'Differential Database Backup of Inventory',
PASSWORD = N'InventoryBackupDiffPassword',
UNLOAD, STATS = 10

Transaction Log/Incremental Backup:
BACKUP LOG MyNwind
TO MyNwind_log1
GO

BACKUP LOG [Inventory]
TO [InventoryBackup1], [InventoryBackup2], [InventoryBackup3]

WITH

NOINIT,
MEDIAPASSWORD = N'InventoryStripeSetPassword',
NAME = N'InventoryTLogBackup',
DESCRIPTION = N'Transaction Log Backup of Inventory',
PASSWORD = N'InventoryBackupTlogPassword',
NOREWIND, STATS = 10

File Backup:
BACKUP DATABASE MyNwind
FILE = 'MyNwind_data_1',
FILEGROUP = 'new_customers',
FILE = 'MyNwind_data_2',
FILEGROUP = 'first_qtr_sales'
TO MyNwind_1
GO

Truncating Log: Transaction Log truncation occurs at-
1) The completion of any BACKUP LOG statement.
2) Every time a checkpoint is processed, provided the database is using the simple recovery model.
Truncation does not reduce the size of a physical log file, it reduces the size of the logical log file.

DBCC SHRINKFILE: DBCC SHRINKFILE allows you to shrink files in the current database. When target_size is specified, DBCC SHRINKFILE attempts to shrink the specified file to the specified size inmegabytes. Used pages in the part of the file to be freed are relocated to available free space in the part of the file retained. For example, for a 15-MB data file, a DBCC SHRINKFILE with a target_size of 12 causes all used pages in the last 3 MB of the file to be reallocated into any free slots in the first 12 MB of the file. DBCC SHRINKFILE doesn't shrink a file past the size needed to store the data.
For example, if 70 percent of the pages in a 10-MB data file are used, a DBCC SHRINKFILE statement with a target_size of 5 shrinks the file to only 7 MB, not 5 MB.

DBCC SHRINKFILE ( {file_name | file_id }
[, target_size][, {EMPTYFILE | NOTRUNCATE | TRUNCATEONLY} ] )

DBCC SHRINKDATABASE: The DBCC SHRINKDATABASE command shrinks all files in a database. The database can't be made smaller than the model database. In addition, the DBCC SHRINKDATABASE command does not allow any file to be shrunk to a size smaller than its minimum/initial size. For example, if you've used 60 MB of a 100-MB database file, you can specify a shrink percentage of 25 percent. SQL Server will then shrink the file to a size of 80 MB, and you'll have 20 MB of free space in addition to the original 60 MB of data.

DBCC SHRINKDATABASE (database_name [, target_percent]
[, {NOTRUNCATE | TRUNCATEONLY} ] )

NOTRUNCATE option causes all the freed file space to be retained in the database files. SQL Server only compacts the data by moving it to the front of the file. The default is to release the freed file space to the operating system.
TRUNCATEONLY option causes any unused space in the data files to be released to the operating system. No attempt is made to relocate rows to unallocated pages. When TRUNCATEONLY is used, target_size and target_percent are ignored.
EMPTYFILE option, available only with DBCC SHRINKFILE, empties the contents of a data file and moves them to other files in the filegroup.

-.-.-.-.-.-.-.-.-.-.-.-
Restore

Database Restore:
RESTORE DATABASE database_name
[ FROM backup_device ]
[ WITH options ]

E.g. Restore Database with New Database name on same Server:
RESTORE DATABASE nwind_new FROM DISK = 'c:\backups\northwind\nwind.bak'
WITH
MOVE 'northwind' TO 'd:\Program Files\Microsoft SQL Server\Data\nwind_new.mdf'

MOVE 'northwind_log' TO 'd:\Program Files\Microsoft SQL Server\Data\nwind_new_log.ldf

File or file group Restore:
RESTORE DATABASE database_name
[FILE = file_name ]
[FILEGROUP = filegroup_name ]
[ FROM backup_device ]
[ WITH options ]

Transaction Log restore:
RESTORE LOG database_name
[ FROM backup_device ]
[ WITH options ]

OPTIONS-
PASSWORD = password
NORECOVERY | RECOVERY | STANDBY = undo_file

RECOVERY: The RECOVERY option should not be specified on any backup except the very last one. When the undo phase is performed with the RECOVERY completion state, no additional backups can be applied. If a database is recovered too early (meaning that you still have backups to apply) then you will need to restart the restore sequence with the first backup.

NORECOVERY: This phase does not allow anyone, including system administrators, to access the database. This option leaves the database nonoperational but able to restore additional backups. NORECOVERY is not the default, but it is always safer to err on the side of NORECOVERY. Perform every restore with NORECOVERY and when you are absolutely certain that you just applied the very last transaction log (usually the tail of the transaction log), recover the database using the RECOVERY option.

STANDBY: This is a special combination of the two. With this recovery completion state specified, SQL Server performs undo yet keeps the transactional information that was undone in a file that can be used when the next log is applied. STANDBY recovery completion state offers the ability to use the database for read activity in between the restores. This allows you to verify the state of the data between restores. This is extremely useful if you are trying to determine when data became damaged. Additionally, this allows you to create a secondary copy of the database that can be used for read activity until the next restore must be performed.

Using RESTORE LABELONLY to view information about the backup media set and the retention period, use RESTORE LABELONLY. If you have used good naming conventions then you should easily be able to see if devices belong to the same media set. Otherwise, you will need to review the MediaFamilyID, which is a GUID, to make sure you have all devices in the parallel striped backup. To see the device label use:
RESTORE LABELONLY FROM BackupDevice

Using RESTORE HEADERONLY To view information about the backups that exist on a multifile backup, use the RESTORE HEADERONLY command. This command works against a single device— even when the device is part of a parallel striped media set. If the device is part of a media set, all devices in that media set will return exactly the same information Lists of backup performed on Backup device: This lists all of the backups that have been performed to this device or these devices.
RESTORE HEADERONLY FROM WITH Password = 'password'
This list following columns-

Backup type-
1 = Database
2 = Transaction Log
4 = File
5 = Differential Database
6 = Differential File

Device Type-
Disk 2 = Logical 102 = Physical
Tape 5 = Logical 105 = Physical
Pipe 6 = Logical 106 = Physical
Virtual Device 7 = Logical 107 = Physical

To verify Validity of backup-
RESTORE VERIFYONLY FROM

Recovery Model:
SQL Server Automatic Recovery:
Recovery Models- Simple, Bulk-logged or Full
USE master
ALTER DATABASE mydatabase SET RECOVERY FULL ;

Full and Bulk-logged Recovery Model: In those recovery models, a sequence of transaction log backups is being maintained. The part of the logical log before the MinLSN cannot be truncated until those log records have been copied to a log backup. NOTRUNCATE, TRUNCATEONLY, EMPTYFILE.

Simple Recovery Model: NO_LOG and TRUNCATE_ONLY are the only BACKUP LOG options that are valid for a database.
MinLSN-minimum recovery log sequence number.

Important things to remember while you Restore Database:
1. When we restore database, we always need to start restore procedure from Full backup followed by Differential backup and/or Transaction log backup.
2. The Differential backup take backup of all changes made since last full backup (and not from last differential backup)
3. The Transaction log backup take log backup of all changes made since last backup (any of full, differential or transaction).
4. To restore database, first restore last Full backup then restore following last differential backup (if any) and lastly all transaction log backup followed by differential backup (of full backup if diff backup is not taken/restored).
5. In restoration procedure, all restores must specify NORECOVERY option except last restore. Otherwise we need to start recovery process again.
6. By NORECOVERY option the database is restored but we cannot read it as there may be some uncommitted transactions. If you want to read/check status of the database after each restore then restore database with STAND BY option. This allows us to read database in between restore procedures.
7. You can provide password to media/backup device for your safety. To restore such password protected backup you need to provide PASSWORD in options of recovery.
8. If the database backup is large and you want to check the status whether restore is going or not, you can specify STATS = percentage option so that, restoration process gets updated on screen.

Microsoft Surface

2007-05-25T23:55:00.000+05:30

Microsoft Surface Video - Touch screen, Multi Touch Coffee Table:
Microsoft has quietly been developing the first completely new computing platform since the PC — a project that was given the internal code name Milan.

The product behind the Milan project is called the Microsoft Surface, and the company's unofficial Surface showman is Jeff Gattis. He's a clean-cut fellow who is obviously the veteran of a thousand marketing seminars. He spoke in sentences peppered with "application scenarios," "operational efficiencies" and "consumer pain points" while he took me through a few demonstrations of what the Surface can do. One of Gattis's consumer pain points is the frustrating mess of cables, drivers and protocols that people must use to link their peripheral devices to their personal computers. Surface has no cables or external USB ports for plugging in peripherals. For that matter, it has no keyboard, no mouse, no trackball — no obvious point of interaction except its screen.

Gattis took out a digital camera and placed it on the Surface. Instantly, digital pictures spilled out onto the tabletop. As Gattis touched and dragged each picture, it followed his fingers around the screen. Using two fingers, he pulled the corners of a photo and stretched it to a new size. Then, Gattis put a cellphone on the surface and dragged several photos to it — just like that, the pictures uploaded to the phone. It was like a magic trick. He was dragging and dropping virtual content to physical objects. I'm not often surprised by new technology, but I can honestly say I'd never seen anything like it.

Yahoo's Lyrics Database

2007-04-25T23:55:00.000+05:30

Today, Yahoo Music has added a legit lyrics database--licensed from music data kingpin Gracenote. It fills a huge, gaping hole out there,” said Ian Rogers, general manager of Yahoo music. Song lyrics have been available through scores of other Web sites for years, but most of those destinations are technically breaking the law by posting the words without the approval of the publishers and writers that own the rights. According to yahoo it contains 400,000 songs lyrics span about 9,000 different artists, which is largest than any other site currently have. If you want to buy a song, you can look up lyrics and buy the song if it’s available.

Yahoo’s song lyrics, in contrast, are supposed to be the official versions. Under the licensing agreement, Yahoo will share with copyright holders the revenue from the ads that will be displayed alongside the lyrics.

Yahoo is hoping its database stimulates even more traffic on its music service, which is already the most popular on the Web. Yahoo music attracted 22 million U.S. visitors last month to rank it ahead of AOL music (17.5 million visitors) and MySpace music (14.8 million visitors), according to comScore Media Metrix.

Here are some of my favorite lyrics- Escape, Be with you, It’s my Life, Baby One More Time, Oops I did it again.

Windows CardSpace

2007-03-25T23:55:00.000+05:30

Introducing Windows CardSpace: Windows CardSpace (formerly "InfoCard") is a Microsoft .NET Framework version 3.0 (formerly WinFX) component that provides the consistent user experience required by the identity metasystem. It is specifically hardened against tampering and spoofing to protect the end user's digital identities and maintain end-user control.

Digital Identity: Like identities in the real world, digital identities come in all shapes and sizes. Perhaps you have an e-mail account with Gmail, for example, identified by an e-mail address. You might also have digital identities with various commercial organizations, such as Amazon or eBay, along with identities for sites such as Orkut.com. Each of these is typically identified by a username that you defined. At work, you might have a digital identity assigned to you by your employer, identified by your network login. This identity is probably maintained by some directory service, such as Active Directory, and today it's typically useful only within the boundaries of your company network.

Just as in the real world, there are good reasons to use different digital identities in different contexts. It's common, for instance, to associate different information with each identity. An identity that you use with Amazon might allow access to your credit card number, while one used with Orkut.com does not. The rules for getting each identity are also different. Getting a digital identity at Amazon is easy: just make up a username and password. Getting a digital identity at your employer is probably somewhat more difficult, since, at a minimum, it requires the approval of the administrators who run your company's network.

Windows CardSpace, formerly codenamed “InfoCard”, is a piece of client software that enables users to provide their digital identity to online services in a simple, secure and trusted way. It is what is known as an identity selector: when a user or subject needs to authenticate to a website or a web service, CardSpace pops up a special security-hardened UI with a set of “cards” for the user to choose from. Each card has some identity data associated with it – though this is not actually stored in the card – and has been given to the user by an identity provider such as their bank, employer or government. In fact, the user can also act as an identity provider – this is essentially what we do every time we register at a website. The CardSpace UI enables users to create Personal cards and associate a limited set of identity data. When the user chooses a card, a request in the form of a web service call goes to the relevant provider, and a signed and encrypted security token is returned containing the required information (e.g. credit limit, employer’s name and address, or perhaps a social security number). The user then decides whether to release this information to the requesting online service. If the user approves then the token is sent on to this relying party where the token is processed and the user is authenticated.

CardSpace is an implementation of an identity selector on Microsoft Windows. Other operating systems will see their own identity selector implementations. The architecture upon which CardSpace has been built – consisting of subjects, identity providers and relying parties – is called “The Identity Metasystem”. This isn’t just a Microsoft initiative, but rather it is the shared vision of many across the industry as to how we can solve some of the fundamental identity challenges on the Internet today. The initial vision for the Identity Metasystem was developed by Microsoft’s Identity Architect, Kim Cameron, and has been broadly adopted and championed by thought-leaders such as Doc Searls and Lawrence Lessig.

Google Analytics Vs Yahoo Analytics

2007-02-25T23:55:00.000+05:30

Google launched Google Analytics which was UrChin before, provides both hosted and log-based tools for understanding how people are interacting with web sites. Yahoo already owns web analytics technology that it obtained through its 2003 purchase of Overture. One reason to jump into web analytics is that the search companies understand that as search ad prices rise, people will only be willing to pay more if they can justify this by showing better conversions. Web analytics can help those who aren't tracking conversions or who are tracking conversions at only a basic level to better understand the full picture of what happens on their web sites. There are many other sites are available like, OneStat, ShinyStat and ClicksTracks .

How Urchin or Google Analytics works:
There are two components to the Urchin Traffic Monitor System: the UTM Sensor, which is a lightweight module installed into the content of the website; and the UTM Engine which is part of the log processing Urchin Engine. The UTM Sensor enables client-side data collection, which is then funneled back through the web server augmenting the normal logfile. The client-side information is combined with the existing server-side data by the UTM Engine to provide a more accurate and complete picture of website activity.

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The UTM Sensor is a small amount of JavaScript code that accomplishes two important functions. First, the Sensor negates the effects of caching by forcing at least one hit to progress to the original web server for each pageview. The impact on the server is minimal, and the details about the additional hit are logged into the normal web logfiles resulting in a more complete data set. Secondly, the UTM Sensor uniquely identifies each visitor by using client-side "1st party" cookies to keep track of first time and returning visitors. This cookie identifier is a communication tag only viewable to your web server in the same nature as session ids. It is not a third party cookie, which provides information outside your system, violating many privacy policies.

How Big B had his first break?

2007-01-25T23:55:00.000+05:30

There are stories and stories about how Dr. Amitabh Bachchan took his first step ever in Hindi films. He has told his story himself in his autobiography, “Amitabh Bachchan – To B Or Not to B.”

But I have had the privilege of knowing the truth from the man who gave him the opportunity, the truth according to Padma Shri Khwaja Ahmad Abbas. The man, who really knows the truth, about how Amitabh Bachchan started his career as an actor.

Abbas was a man who kept making films even though his films didn’t work at the box office and he kept loosing money, which he earned by writing articles, short stories, books and scripts for filmmakers like Raj Kapoor. Some of the biggest hits of Kapoor were based on the scripts written by Abbas.

Raj Kapoor was so grateful to Abbas that he called Abbas “my soul, my mind and the pillar of my company, R.K. Films.” Abbas was known as one of the first few filmmakers who made films on topical subjects, which he created from the headlines of newspapers and from everyday happenings.

Abbas was inspired by the liberation of Goa from the Portuguese, a victory won by Pandit Jawaharlal Nehru, the then Prime Minister and Defense Minister V.K. Krishna Menon. It was also a victory of the jawans of the Indian army. Abbas decided to make a film on the subject, the role played by seven Indian, six young man and a woman in the struggle. He was happy when he found all the seven artists to play the seven characters and was ready to start shooting in Goa.

There were just four days left for his unit to leave for Goa when a crisis was created by a young man, who was very close to Abbas. The young man, Tinnu Anand, the son of his best friend, Inder Raj Anand, the first Indian film writer, was paid a price that was as good as the fee paid to any big star.

Tinnu gave his ‘Mamoojaan’ (uncle) the shock of his life when he very timidly told him that he could not go to Goa and do the film which was now called ‘Saat Hindustani.’ Abbas felt he was joking, he was used to the little pranks played by Tinnu. The young Tinnu, however, was serious. He told ‘Mamoojaan” that he had another tempting option. He had received a letter from the greatest ever Indian filmmaker, Satyajit Ray to be his assistant.

It was Abbas himself who had asked Ray to take Tinnu as one of his assistants and now his own idea was creating a crisis for him! Abbas was furious how could Tinnu do this to him. He almost thundered and it looked he would bring down the five-storied building down. He calmed down and finally told Tinnu that he would let him go to Calcutta only on condition, that he finds a replacement for him within two days.

Tinnu was in a fix. He did not know what to do. Then an unexpected idea struck him like a flash. He put his hand into his back-pocket and culled out his purse. Abbas asked him if he was working some magic. Little did Abbas and Tinnu know that Tinnu was working the kind of magic which would shake up the world one day.

He remembered he was carrying a photograph of a young man given to him by Neena, a friend from Delhi. She had told him it was the photograph of her friend, who was from a very good family and who was having a good job in Calcutta, but was interested in making it in a Hindi film.

Tinnu placed the photograph of the unknown young man before Abbas who had one look and asked Tinnu where the young man was and asked him to send a message to him to come down to Bombay and that he was willing to pay his one way third class fair from Calcutta to Bombay. Tinnu immediately called his friend in Delhi and got his telephone number, spoke to him and asked him to come to Bombay.

The young man flew down to Bombay with his brother, contacted Tinnu, and he took the two to Abbas. The two brothers found Abbas and he asked “inn dono mein actor kaun banna chahta hain?.” One of them spoke up. “Main sir,” the voice was rich. He introduced himself and told Abbas all that he could.

Abbas asked him if he was willing to give up his job with a handsome salary of Rs 3,500 a month. He clearly told him that even if he was selected he would be paid only Rs 6,000 and he would have to work for 40 days at a stretch in Goa. It was an offer accepted by all the other six artists, which included leading actors like Utpal Dutt from Calcutta and Madhu from Kerala and Anwar Ali, brother of the famous comedian Mehmood from Banglore.

The young man was silent and so was his brother. Abbas read meaning into their silence and gave them a night to think over and report to him the next morning at 11, if they were willing to work according to his terms and conditions.

The two brothers found a place to rest for the night. They did not sleep. They discussed the offer. They went over the achievements of Abbas and finally took a decision to meet Abbas. The next morning they reached his office 10 minutes before 11. Abbas was already there, waiting for them. He made them set on two steel chairs, while he sat across a large old fashioned wooden table. He came to the point. He asked the brother who had said he wanted to be an actor what his decision was.

The two brothers looked at each other and said they were willing to act in his film. That was not the end of the test for the young man. He was asked what he had done as an actor. He then told him that he would have to live in a dormitory where the entire unit would live. The young man agreed and then came the dramatic moment. Abbas asked the two their names for the first time. The brother who wanted to be an actor said his name was Amitabh Bachchan. The other brother said he was Ajitabh Bachchan. The names forced Abbas to pause a moment and he then asked them, if they were in any way related to well-known poet Harivanshrai Bachchan. They said they were his sons. Abbas shook his head and asked them for their father’s phone number. He picked up the phone and called their father. The brothers looked anxious.

Abbas spoke to Harivanshrai, who was his friend. He told him that his sons were sitting with him and one of them, Amitabh wanted to be an actor. He asked the senior Bachchan if the boy had his permission or had run away from home. The father laughed and said if he, Abbas was giving him a break as an actor, he had absolutely no objection. Abbas heaved a sigh of relief.

The two brothers looked nervous for the first time. Abbas then drafted a contract with the help of his secretary, Abdul Rehman. The young man signed the contract without having any premonition that he was not signing his name, but writing his name in history. He was then given two days to get ready to leave for Goa. He said he would not need to take anything much because they would be shooting almost round the clock.

Abbas completed the film and at the end of it patted Amitabh on his back and said he was confident that he would make it as a good actor, if he made the right choice when it came to roles. The film was released. It did not do very well like most of the films made by Abbas, but Amitabh was marked out as an actor with a difference.

His work was seen by a friend of Abbas, Hrishikesh Mukherjee who cast him in ‘Anand.’ He then did a film called ‘Bomba to Goa.’ The ruling writers of the time, Salim and Javed saw just two scenes from the film and recommended him as the hero to Prakash Mehra who was making ‘Zanjeer’ for which he was looking for a hero after Dev Anand, Dharmendra and Raaj Kumar had turned down his offer.

Mehra reluctantly agreed to cast him as the angry young police officer in his film. The film was released on a Friday morning. During the interval Amitabh kicked the chair on which Pran was to sit on and the audience roared with applause. At the end of the first day a superstar called Amitabh Bachchan was born and he has never looked back during the last 36 years. And he never forgets Philomena Apartment, Juhu where Abbas lived and where he signed his first film to create history.

Windows Vista®

2007-01-17T23:55:00.000+05:30

Windows Vista® is the name of the next major version of Windows, and the successor to Windows XP. You have to choose Vista from four editions-

Windows Vista Home: For basic home needs such as e-mail and Internet access.
Windows Vista Home Premium: For the best home computing and entertainment.
Windows Vista Business: For small and mid-sized organizations
Windows Vista Ultimate: For work and entertainment, this is the most complete edition.

Features:
Security: Windows Vista® builds on the security features in Windows XP with Service Pack 2 (SP2) and Windows Server 2003 with Service Pack 1 (SP1) and adds some deep-seated security improvements that will finally make the Windows platform competitive with Linux and Mac OS X from a security standpoint. With Windows Vista, the system will inform users about security and privacy choices so they feel more confident that they are as secure as possible, and that their privacy is protected.
User Account Control: User Account Control is a new infrastructure that requires user consent before allowing any action that requires administrative privileges. With this feature, all users, including users with administrative privileges, run in a standard user mode by default, since most applications do not require higher privileges. When some action is attempted that needs administrative privileges, such as installing new software or changing system settings, Windows will prompt the user whether to allow the action or not. If the user chooses to allow, the process initiating the action is elevated to a higher privilege context to continue. While standard users need to enter a username and password of an administrative account to get a process elevated (Over-the-shoulder Credentials), an administrator can choose to be prompted just for consent or ask for credentials.
UAC asks for credentials in a Secure Desktop mode, where the entire screen is faded out and temporarily disabled, to present only the elevation UI. This is to prevent spoofing of the UI or the mouse by the application requesting elevation. Any application requesting elevation has to have focus before the switch to Secure Desktop occurs. Else its taskbar icon blinks, and when focussed, the elevation UI is presented. Since the Secure Desktop allows only highest privilege System applications to run, no user mode application can present its dialog boxes, so any prompt for elevation consent can be safely assumed to be genuine. Additionally, they can also help protect against shatter attacks, which intercept Windows inter-process messages to run malicious code or spoof the user interface, by preventing unauthorized processes from sending messages to high privilege processes. Any process that wants to send a message to a high privilege process must get itself elevated to the higher privilege context, via UAC.
Windows Defender: Windows Vista includes Windows Defender, Microsoft's anti-spyware utility. According to Microsoft, it was renamed from 'Microsoft AntiSpyware' because it not only features scanning of the system for spyware, similar to other free products on the market, but also includes Real Time Security agents that monitor several common areas of Windows for changes which may be caused by spyware. These areas include Internet Explorer configuration and downloads, auto-start applications, system configuration settings, and add-ons to Windows such as Windows Shell extensions.
Parental Control: Windows Vista includes a range of parental controls. An administrator can apply parental control restrictions to other users on the computer.
Facilities include:

Web content blocking, including the ability to limit web browsing to "kids websites", as well as blocking particular categories of content such as "Pornography", "Drugs", "Web e-mail", "Web chat", and so on. File downloads may also be disabled.

Time limitations on when the account may be used.

Restrictions on what kind of games may be played.

Restrictions on what programs may be executed.

Activity reports to monitor what was done under Parental Controls.

Digital Rights Management: Microsoft is introducing a number of Digital Rights Management and content-protection features in Windows Vista, to help digital content providers, corporations, and end-users protect their data from being copied.

Protected User Mode Audio (PUMA)

Protected Video Path - Output Protection Management (PVP-OPM)

Protected Video Path - User-Accessible Bus (PVP-UAB)

Rights Management Services (RMS)

Application isolation: Windows Vista introduces Mandatory Integrity Control to set integrity levels for processes. A low integrity process can not access the resources of a higher integrity process. This feature is being used to enforce application isolation, where applications in a medium integrity level, such as all applications running in the standard user context can not hook into system level processes which run in high integrity level, such as administrator mode applications but can hook onto lower integrity processes like Windows Internet Explorer 7.
Service hardening: Windows Service Hardening prevents Windows services from doing operations on file systems, registry or networks which they are not supposed to, thereby preventing entry of malware by piggybacking on system services. Services are now assigned a per-service Security identifier (SID), which allows controlling access to the service as per the access specified by the security identifier. Services can also use access control lists (ACL) to prevent external access to resources private to itself. Services in Windows Vista also run in a less privileged account such as Local Service or Network Service, instead of the System account. Services will also need explicit write permissions to write to resources, on a per-service basis. Only those resources which have to be modified by a service give it write access. So trying to modify any other resource fails. Services will also have pre-configured firewall policy, which gives it only as much privilege as is needed for it to function properly.
Network Access Protection: Network Access Protection, (NAP) which makes sure that computers connecting to a network or communicating over a network conform to a required level of system health, as has been set by the administrator of the network, has been upgraded significantly in Windows Vista. Depending on the policy set by the administrator, the computers which do not meet the requirements will either be warned and granted access or allowed a limited access to network resources or completely denied access. NAP can also optionally provide software updates to a non-compliant computer to upgrade itself to the level as required to access the network, using a Remediation Server. A conforming client is given a Health Certificate, which it then uses to access protected resources on the network.
Other Security Features:

Windows Resource Protection: prevents "potentially damaging system configuration changes", by preventing change to system files and settings by any process other than Windows Installer. Also changes to registry by unauthorized software are blocked.

Protected-Mode IE: Internet Explorer runs in a separate, low-privilege process, protecting the user from malicious content and security vulnerabilities, even in ActiveX controls.

Windows Firewall: has been upgraded to support outbound packet filtering and full IPv6 support. A new MMC-based interface has been introduced which offers much more advanced control over the firewall.

Session 0 Isolation: Previous versions of Windows ran System services in the same login session as the locally logged-in user (Session 0). In Windows Vista, Session 0 is now reserved for these services, and all interactive logins are done in other sessions. This is intended to help mitigate a class of exploits of the Windows message-passing system, known as Shatter attacks.

Full support for the "NX" (No-Execute) feature of modern processors. This feature, present as NX (EVP) in AMD's AMD64 processors and as XD (EDB) in Intel's processors, can flag certain parts of memory as containing data instead of executable code, which prevents overflow errors from resulting in arbitrary code execution. This feature was introduced in Windows XP Service Pack 2 and Windows Server 2003 Service Pack 1.

Address Space Layout Randomization (ASLR): to prevent Return-to-libc buffer overflow attacks.

BitLocker Drive Encryption: Formerly known as "Secure Startup", this software utilizes a Trusted Platform Module (compliant with the 1.2 version of the TCG specifications) to improve PC security. It ensures that the PC running Windows Vista starts in a known-good state, and it also protects data from unauthorized access through full volume encryption. Data on the volume is encrypted with a Full Volume Encryption Key (FVEK), which is further encrypted with a Volume Master Key(VMK) and stored on the disk itself.

Windows Vista can use Smart Cards or Smart Card/Password combo for user authentication.

Windows Vista can use smart cards to store Encrypting File System (EFS) keys. This makes sure that encrypted files are accessible only as long as the smart card is physically available.

Internet Explorer 7: Internet Explorer 7 adds new security and privacy features. Also it comes with new features such as tabbed browsing, inline search, and shrink-to-fit printing.

Performance: Windows Vista comes with new features like Sleep, Windows SuperFetch, Windows ReadyBoost, and Windows ReadyDrive

User Interface Feature: Windows Vista has a user experience that can scale depending on hardware configuration.
Windows Vista Basic UI: All versions of Windows Vista, from Starter on up to Ultimate, can utilize the Windows Vista Basic UI, though it will not be the default unless your video card is incapable of displaying Windows Vista Standard or Windows Aero. Windows Vista Basic is based on the same interface technologies used by the Windows XP user interface, and it therefore suffers from the same instability issues that can sometimes afflict that system.
Windows Vista Standard UI: On Windows Vista Home Basic only, which is artificially limited for marketing purposes and does not include the beautiful Windows Aero UI, users will see a rare Vista UI option called Windows Vista Standard. This UI visually resembles Windows Aero, but offers none of the associated graphical effects, including translucency, Windows Flip 3D, and Live Taskbar Thumbnails. From a technological perspective, Windows Vista Standard provides only software-based rendering, so it offers none of the performance or stability benefits of Windows Aero.

Windows Vista Aero UI: Most Windows Vista users will simply get the Windows Aero user interface, which is the default on all Vista product editions (aside from Vista Starter and Home Basic). This UI offers the stunning glass-like effects you've seen in most Windows Vista screenshots, including the glass-like chrome on floating windows, the translucent Start Menu and taskbar, Windows Flip 3D, and Live Taskbar Thumbnails. And because Windows Aero takes advantage of your video card's GPU, it provides better performance and stability than does a software-based UI, which requires the PC's microprocessor to do all the work.
Aero is an environment with an additional level of visual sophistication, one that is even more responsive and manageable, providing a further level of clarity to Windows users.
Windows Classic UI: For corporations that don't want to retrain their users on the new Windows Vista UI types, Microsoft still provides a Windows Classic UI, that somewhat resembles the UI in Windows 2000. However, there are many differences due to some of the massive changes Microsoft made to Windows Explorer in this version. For this reason, it's going to take users a while to get used to the new system even when Windows Classic is enabled.
Windows Flip 3D: In addition to Windows Flip, Microsoft now supports a new 3D task switcher called Windows Flip 3D. This mode, which is enabled with the WINDOWS KEY + TAB keyboard shortcut, or via a new "Switch between windows" icon in the Quick Launch toolbar in the taskbar, puts task switching in a new dimension.
Windows Flip 3D requires Windows Aero.

32-bit & 64-bit: Virtually every Windows Vista product edition (with the exception of Starter) ships with both 32-bit (x86) and 64-bit (x64) versions on the same DVD. Microsoft expects the computer buying public to switch to x64 during Vista's lifetime. There will not be an Itanium version of Windows Vista.

Live Taskbar Thumbnail: When you mouse over a taskbar button, you'll see a thumbnail pop-up, showing you the window you'll see if you should click that button.
Live Taskbar Thumbnails require Windows Aero. If you are running a different user interface, you'll see tooltips when you mouse over taskbar buttons, as you do in previous Windows versions.

Kernel Patch Protection: The Kernel Patch Protection feature (also known as "Patchguard") on 64-bit versions of Vista that locks down the OS kernel has been criticized by computer security company McAfee who claim that since PatchGuard also prevents third-party security companies from getting inside the OS, they cannot activate crucial security measures in their software to protect the OS from intruders. Microsoft's argument is that this will keep miscreants out of the OS and prevent the incidence of attacks, and it is something for which customers have been asking. Security vendor Kaspersky Lab claims that it is not more difficult in Vista for anti-virus software to work, and that it would not make sense for Microsoft to stop working with security companies because it would make their system more vulnerable to attacks. Sophos adds that Microsoft does not need to open PatchGuard for third party developers, instead, they should use the APIs Microsoft supplies them.

Digital Rights Management: Another common criticism concerns the integration of new forms of Digital Rights Management into the operating system, specifically the introduction of the Protected Video Path (PVP). This architecture is designed such that "premium content" from HD-DVD or Blu-ray discs may mandate that the connections between PC components are encrypted. Devices such as graphic cards must be approved by Microsoft. Depending on what the content demands, the devices may not pass premium content over non-encrypted outputs, or they must artificially degrade the quality of the signal on such outputs or not display it all. There is also a revocation mechanism that allows Microsoft to disable drivers of compromised devices in end-user PCs over the Internet.

Hardware Requirements:
Windows Vista Capable PC: A new PC that carries the Windows Vista Capable PC logo can run Windows Vista.
A Windows Vista Capable PC includes at least:

A modern processor (at least 800MHz¹).
512 MB of system memory.
A graphics processor that is DirectX 9 capable.

Windows Vista Premium Ready PC: To get an even better Windows Vista experience, including the Windows Aero user experience, ask for a Windows Vista Capable PC that is designated Premium Ready, or exceeds the premium ready requirements.
A Windows Vista Premium Ready PC includes at least:

1 GHz 32-bit (x86) or 64-bit (x64) processor.
1 GB of system memory.
Support for DirectX 9 graphics with a WDDM driver, 128 MB of graphics memory (minimum), Pixel Shader 2.0 and 32 bits per pixel.
40 GB of hard drive capacity with 15 GB free space.
DVD-ROM Drive.
Audio output capability.
Internet access capability.

Longhorn Server: Currently codenamed Longhorn Server, will be called Windows Server 2008. It will definitely not be called Windows Vista Server. Longhorn Server was being developed concurrently with Windows Vista, but will ship in late 2007.

Oracle Fundamentals

2007-01-04T23:55:00.000+05:30

ORACLE ARCHITECTURE

Oracle Server: There are several files, processes, and memory structures in an Oracle server; however, not all of them are used when processing a SQL statement. Some are used to improve the performance of the database, ensure that the database can be recovered in the event of a software or hardware error, or perform other tasks necessary to maintain the database. The Oracle server consists of an Oracle Instance and an Oracle Database.

Oracle Instance: An Oracle instance is the combination of the background processes and memory structures. The instance must be started to access the data in the database. Every time an instance is started, a System Global Area (SGA) is allocated and Oracle background processes are started.

Background processes perform functions on behalf of the invoking process. They consolidate functions that would otherwise be handled by multiple Oracle programs running for each user. The background processes perform input/output (I/O) and monitor other Oracle processes to provide increased parallelism for better performance and reliability.

Oracle Instance Startup: has 3 distinct steps:

1.Starting the instance process.
2.Mounting the database, which consists of opening the control files for the instance
3.Opening the database, which makes the database available for user requests.

üOracle Database: An Oracle database consists of operating system files, also known as database files, that provide the actual physical storage for database information. The database files are used to ensure that the data is kept consistent and can be recovered in the event of a failure of the instance.

Consists of 3 types of Files:

1. Data Files: containing the actual data in the database

2.Redo Log Files: containing a record of changes made to the

database to enable recovery of the data in case of failures

3.Control Files: containing information necessary to maintain

and verify database integrity.

Other key files: Non-database files are used to configure the instance, authenticate privileged users, and recover the database in the event of a disk failure.

User Processes: Started at the time a database user requests connection to the Oracle Server.

Server Processes: Connects to Oracle Instance and is started when a user establishes a session.

Background Processes: Available when an Oracle Instance is started.

Other processes: Many other processes exist that are used by other options within Oracle, such as Advanced Queuing, Real Application Clusters, Shared Server, Advanced Replication, and so on.

Memory Structure: Consists of two memory areas-
1.System Global Area (SGA): Allocated at instance startup, and is a fundamental component of an Oracle Instance. Shared by several processes.

SGA Consists of several memory structures:
-Shared Pool: Used to store most recently used SQL Statements and data definitions

1. Library Cache: Stores SQL Statements

2. Data Dictionary Cache: Stores Data Definition

“ALTER SYSTEM SET SHARED_POOL_SIZE = 64M;”

-Database Buffer Cache: Stores copies of data blocks that have been retrieved from the data files.

“ALTER SYSTEM SET DB_CACHE_SIZE = 96M;”

-Redo Log Buffer Cache: Stores changes made in Data Blocks.

“LOG_BUFFER”

-Other Structures:

There are 2 other structures that can be configured in SGA:-

I.Large Pool: Configured only in Shared server environment, used for session memory, I/O slaves and backup and restore operation.

“ALTER SYSTEM SET LARGE_POOL_SIZE = 64M;”

II.Java Pool: Requires if installing and using JAVA. Stored much the same way as PL/SQL in db.

“JAVA_POOL_SIZE”

2.Program Global Area (PGA): PGA is memory reserved for each user process that connects to an Oracle Database. Allocated when server process is started and de-allocated when process is terminated. PGA is used by One process only.

Logical Structure:
Dictates how the physical space of database is to be used. Hierarchy- Tablespaces, Segments, Extent & Blocks. Individual objects in database are stored in segments, which are collection of extents.
Block is smallest unit for read and write operations.