Calculate Time Difference Between DateTime Objects

To get time difference you need to use TimeSpan object, with code like this:

TimeSpan ts = DateTime1 - DateTime2;

For example, if you want to calculate time difference between server time and UTC time:

[ C# ]

protected void Page_Load(object sender, EventArgs e)
{
    // Declare and get DateTime values
    DateTime StartDate = System.DateTime.Now;
    DateTime EndDate = System.DateTime.UtcNow;
 
    // Find time difference between two dates
    TimeSpan TimeDifference = StartDate - EndDate;
 
    // Write difference in hours and minutes
    Response.Write("Time difference between server time and Coordinated Universal Time (UTC) is " + 
        TimeDifference.Hours.ToString() + " hours ");
    if (TimeDifference.Minutes != 0)
        Response.Write(" and " + TimeDifference.Minutes.ToString() + " minutes.");
 
}

http://www.beansoftware.com/ASP.NET-FAQ/DateTime-TimeSpan.aspx

Web Farm in Asp.net

Web Farm in Asp.net

After developing our asp.net web application we host it on IIS Server.  Now one standalone server is sufficient to process ASP.NET Request and response for a small web sites but when the site comes for big organization where there an millions of daily user hits then we need to host the sites on multiple Server. This is called web farms. Where single site hosted on multiple IIS Server and they are  running behind the Load Balancer.

Fig : General Web Farm Architecture

This is the most common scenarios for any web based production environment. Where Client will hit an Virtual IP ( vIP) . Which is the IP address of Load Balancer. When Load balancer received the request based on the server load it will redirect the request to particular Server.

http://www.dotnetfunda.com/articles/article713-difference-between-web-farm-and-web-garden.aspx

Trigger in Sql Server

What is a Trigger

A trigger is a special kind of a store procedure that executes in response to certain action on the table like insertion, deletion or updation of data. It is a database object which is bound to a table and is executed automatically. You can’t explicitly invoke triggers. The only way to do this is by performing the required action no the table that they are assigned to.

Types Of Triggers

There are three action query types that you use in SQL which are INSERT, UPDATE and DELETE. So, there are three types of triggers and hybrids that come from mixing and matching the events and timings that fire them.

Basically, triggers are classified into two main types:-

(i) After Triggers (For Triggers)
(ii) Instead Of Triggers

(i) After Triggers

These triggers run after an insert, update or delete on a table. They are not supported for views.
AFTER TRIGGERS can be classified further into three types as:

(a) AFTER INSERT Trigger.
(b) AFTER UPDATE Trigger.
(c) AFTER DELETE Trigger.


http://www.codeproject.com/KB/database/TriggersSqlServer.aspx

Web Garden in asp.net

Web Garden in asp.net

Overview of Web Garden

By default, each application pool runs with a single worker process (W3Wp.exe). We can assign multiple worker processes with a single application pool. An application pool with multiple worker processes is called a Web Garden. Many worker processes with the same application pool can sometimes provide better throughput performance and application response time. And each worker process should have its own thread and memory space.

Web Garden (Application pool with multiple worker processes)

As Shown in the picture, in IIS Server, there may be multiple application pools and each application pool has at least a single worker process. A Web Garden should contain multiple worker processes.

There are certain restrictions in using a Web Garden with your web application. If we use Session Mode as "in proc", our application will not work correctly because the Session will be handled by a different worker process. To avoid this, we should use Session Mode as "out proc" and we can use "Session State Server" or "SQL-Server Session State".


reference:http://www.codeproject.com/KB/aspnet/ExploringIIS.aspx

When to Use Generic Collections in C#

The following generic types correspond to existing collection types:

• List is the generic class corresponding to ArrayList.
• Dictionary is the generic class corresponding to Hashtable.
• Collection is the generic class corresponding to CollectionBase. Collection can be used as a base class, but unlike CollectionBase it is not abstract, making it much easier to use.
• ReadOnlyCollection is the generic class corresponding to ReadOnlyCollectionBase.ReadOnlyCollection is not abstract, and has a constructor that makes it easy to expose an existing List as a read-only collection.
• The Queue, Stack, and SortedList generic classes correspond to the respective nongeneric classes with the same names.
• There are several generic collection types that do not have nongeneric counterparts:
• • LinkedList is a general-purpose linked list that provides O(1) insertion and removal operations.
  • SortedDictionary is a sorted dictionary with O(log n) insertion and retrieval operations, making it a useful alternative to SortedList.
  • KeyedCollection is a hybrid between a list and a dictionary, which provides a way to store objects that contain their own keys.

Difference Between Primary key and Unique key

Difference Between Primary key and Unique key

1.Even though both the primary key and unique key are one or more columns that can uniquely identify a     row in a table, they have some important differences.
2.Most importantly, a table can have only a single primary key while it can have more than one unique key. 
Primary key can be considered as a special case of the unique key. 
3.Another difference is that primary keys have an implicit NOT NULL constraint while the unique key does    not have that constraint. 
4.Therefore, unique key columns may or may not contain NULL values but primary key columns cannot contain NULL values.

Database Keys

Super Key

A Super key is any combination of fields within a table that uniquely identifies each record within that table.

Candidate Key

A candidate is a subset of a super key. A candidate key is a single field or the least combination of fields that uniquely identifies each record in the table. The least combination of fields distinguishes a candidate key from a super key. Every table must have at least one candidate key but at the same time can have several.



As an example we might have a student_id that uniquely identifies the students in a student table. This would be a candidate key. But in the same table we might have the student’s first name and last name that also, when combined, uniquely identify the student in a student table. These would both be candidate keys.
In order to be eligible for a candidate key it must pass certain criteria.

• It must contain unique values
• It must not contain null values
• It contains the minimum number of fields to ensure uniqueness
• It must uniquely identify each record in the table

Once your candidate keys have been identified you can now select one to be your primary key

Primary Key

A primary key is a candidate key that is most appropriate to be the main reference key for the table. As its name suggests, it is the primary key of reference for the table and is used throughout the database to help establish relationships with other tables. As with any candidate key the primary key must contain unique values, must never be null and uniquely identify each record in the table.
As an example, a student id might be a primary key in a student table, a department code in a table of all departments in an organisation. This module has the code DH3D 35 that is no doubt used in a database somewhere to identify RDBMS as a unit in a table of modules. In the table below we have selected the candidate key student_id to be our most appropriate primary key

Secondary Key or Alternative Key

A table may have one or more choices for the primary key. Collectively these are known as candidate keys as discuss earlier. One is selected as the primary key. Those not selected are known as secondary keys or alternative keys.
For example in the table showing candidate keys above we identified two candidate keys, studentId and firstName + lastName. The studentId would be the most appropriate for a primary key leaving the other candidate key as secondary or alternative key. It should be noted for the other key to be candidate keys, we are assuming you will never have a person with the same first and last name combination. As this is unlikely we might consider fistName+lastName to be a suspect candidate key as it would be restrictive of the data you might enter. It would seem a shame to not allow John Smith onto a course just because there was already another John Smith.

Simple Key

Any of the keys described before (ie primary, secondary or foreign) may comprise one or more fields, for example if firstName and lastName was our key this would be a key of two fields where as studentId is only one. A simple key consists of a single field to uniquely identify a record. In addition the field in itself cannot be broken down into other fields, for example, studentId, which uniquely identifies a particular student, is a single field and therefore is a simple key. No two students would have the same student number.

Compound Key

A compound key consists of more than one field to uniquely identify a record. A compound key is distinguished from a composite key because each field, which makes up the primary key, is also a simple key in its own right. An example might be a table that represents the modules a student is attending. This table has a studentId and a moduleCode as its primary key. Each of the fields that make up the primary key are simple keys because each represents a unique reference when identifying a student in one instance and a module in the other.

Composite

A composite key consists of more than one field to uniquely identify a record. This differs from a compound key in that one or more of the attributes, which make up the key, are not simple keys in their own right. Taking the example from compound key, imagine we identified a student by their firstName + lastName. In our table representing students on modules our primary key would now be firstName + lastName + moduleCode. Because firstName + lastName represent a unique reference to a student, they are not each simple keys, they have to be combined in order to uniquely identify the student. Therefore the key for this table is a composite key.