Tips on how to avoid or resolve deadlocking on your SQL Server

Deadlocking occurs when two user processes have locks on separate objects and each process is trying to acquire a lock on the object that the other process has. Usualy, they have different incompatible locks which are illegal or conflict (as per the compatible mode on locks).When this happens, SQL Server identifies the problem and ends the deadlock by automatically choosing one process and aborting the other process, allowing the other process to continue. The aborted transaction is rolled back and an error message is sent to the user of the aborted process. Generally, the transaction that requires the least amount of overhead to rollback is the transaction that is aborted.

Identify Deadlock:

1. Using SQL Profiler
2. Using System_health extended event(It highly depends on the ring buffer)
3. Using Server side trace (DBCC TRACEON (1204) )
4. Using SQL Error Log with a trace
5. Predefined notification functionalities to log the deadlock info using service broker, extended events etc.

Here are some tips on how to avoid/resolve deadlocking on your SQL Server:

1. Ensure the database design is properly normalized.
2. Have the application access server objects in the same order each time.
3. During transactions, don’t allow any user input. Collect it before the transaction begins.
4. Avoid cursors.
5. Keep transactions as short as possible. One way to help accomplish this is to reduce the number of round trips between your application and SQL Server by using stored procedures or keeping transactions with a single batch. Another way of reducing the time a transaction takes to complete is to make sure you are not performing the same reads over and over again. If your application does need to read the same data more than once, cache it by storing it in a variable or an array, and then re-reading it from there, not from SQL Server.
6. Reduce lock time. Try to develop your application so that it grabs locks at the latest possible time, and then releases them at the very earliest time.
7. If appropriate, reduce lock escalation by using the ROWLOCK or PAGLOCK.
8. Consider using the NOLOCK hint to prevent locking if the data being locked is not modified often.
9. If appropriate, use as low of an isolation level as possible for the user connection running the transaction.
10. Consider using bound connections.
11. Adding missing indexes to support faster queries
12. Dropping unnecessary indexes which may slow down INSERTs for example
13. Redesigning indexes to be "thinner", for example, removing columns from composite indexes or making table columns "thinner" (see below)
14. Adding index hints to queries appropriately(I dont prefer this mostly, but it has got its own scope)
15. Redesigning tables with "thinner" columns like smalldatetime vs. datetime or smallint vs. int
16. Modifying the stored procedures to access tables in a similar pattern
17. Keeping transactions as short and quick as possible: "mean & lean"
18. Removing unnecessary extra activity from the transactions like triggers
19. Removing JOINs to Linked Server (remote) tables if possible
20. Implementing regular index maintenance; usually weekend schedule suffices; use FILLFACTOR = 80 for dynamic tables (Needs a good evaluation)

The list really goes on. The solution will vary from situation to situation.

Source: http://beyondrelational.com/quiz/sqlserver/general/2012/questions/a-query-always-ran-in-split-second-and-suddenly-it-started-to-timeout.aspx

Cloud development: 9 gotchas to know before you jump in

Whether developing, testing, or deploying your apps in the cloud, you have to unlearn some beliefs and learn new ones to make it work

Application development and testing in the cloud are gaining popularity, as more businesses launch public and private cloud computing initiatives. Cloud development typically includes integrated development environments, application lifecycle management components (such as test and quality management, source code and configuration management, continuous delivery tools), and application security testing components.

Although technology executives and developers with experience in cloud-based development say there are clear benefits to developing in these environments -- such as costs savings and increased speed to market -- they also caution that there are challenges and surprises to look out for.

[ Get the no-nonsense explanations and advice you need to take real advantage of cloud computing in InfoWorld editors' 21-page Cloud Computing Deep Dive PDF special report. | Stay up on the cloud with InfoWorld's Cloud Computing Report newsletter. ]

Gotcha 1: The cloud doesn't always work like the "real world"

Developers might find that the configuration they use in production is hard to replicate on cloud services. For example, with an application you develop in the cloud before bringing back to run locally, you might need to test against a legacy system that you can't simply copy onto a cloud service

Gotcha 2: Some apps aren't ideal for development in the cloud

The more hard-to-access or hard-to-replicate systems an application integrates with, the more difficult it is to develop and test it on cloud computing resources

Gotcha 3: Developers often dislike the unfamiliar cloud territory

Cloud computing is still relatively new to a lot of organizations, and it can be a disruptive technology, including in the development arena. 

Gotcha 4: Lack of documentation hinders cloud developers

There is a lack of documentation to help developers understand the cloud and the tools and resources that can be used to build applications in that environment.

Gotcha 5: Network issues can bedevil private cloud environments 

Developing in the cloud sometimes means developing in your own private cloud, which may not have the multitenancy and load-movement capabilities that keep your applications available 24/7. Other issues that can affect development and testing involve network delays and latency and the size of network pipes, especially in certain parts of the world. 

Gotcha 6: It's easy to let the meter run unnecessarily on the cloud

Another potential problem is wasting money on cloud fees. Developers can easily forget or neglect to turn off virtual machines they aren't using. When it was on an in-house, capitalized server, this was no big deal. But when it is on usage-metered, leased resources as with public cloud computing, this is a waste of money

Gotcha 7: Cloud licenses can contain surprising deployment restrictions 

Among the nontechnical issues with the cloud that can have an impact on development are licensing restrictions.

Gotcha 8: Integration can be harder to troubleshoot

Integrating new applications with existing ones can be a key part of the development process, and the cloud brings even more challenges from an integration perspective.

Gotcha 9: The cloud's fast pace of change can be hard to keep up with 

Being on a quickly evolving cloud development platform, like Azure, means it's necessary to update best practices frequently

Despite the learning curve, cloud development is appealing
Despite the potential challenges, for many organizations application development in the cloud rather than sticking with traditional methods makes sense, for the same reasons that cloud computing in general makes sense: elasticity of resources and cost, and reduced operational complexity, both of which lead to shorter completion time.

This article, "Cloud development: 9 gotchas to know before you jump in," was originally published at InfoWorld.com. 

Data access optimization steps in SQL Server

Use Indexing

• Apply proper indexing in the table columns in the database
• Make sure that every table in your database has a primary key.
• Create non-clustered indexes on columns which are, frequently used in the search criteria, Used to join other tables, Used as foreign key fields , Of having high selectivity (Column which returns a low percentage (0-5%) of rows from a total number of rows on a particular value) or Used in the ORDER BY clause
  
• Create appropriate covering indexes
• Use Database Tuning Advisor’s help while creating covered index
  
• Defragment indexes if fragmentation occurs

It's really tempting to create index on all eligible columns in your database tables. But, if you are working with a transactional database (An OLTP system where update operations take place most of the times), creating indexes on all eligible columns might not be desirable every time. In fact, creating heavy indexing on OLTP systems might reduce overall database performance (As most operations are update operations, updating data means updating indexes as well).

A rule of thumb can be suggested as follows: If you work on a transactional database, you should not create more than 5 indexes on the tables on an average. On the other hand, if you work on a Data warehouse application, you should be able to create up to 10 indexes on the tables on an average.

Re-factor TSQLs and apply best practices

• Move TSQL codes from application into the database server
• Identify inefficient TSQLs, re-factor and apply best practices
• Don’t use “SELECT*" in SQL Query
• Avoid unnecessary columns in SELECT list and unnecessary tables in join conditions
• Do not use the COUNT() aggregate in a subquery to do an existence check
• Try to avoid joining between two types of columns
• Try to avoid deadlocks 
• Write TSQLs using “Set based approach” rather than using “Procedural approach” 
• Try not to use COUNT(*) to obtain the record count in the table 
• Try to avoid dynamic SQLs
• Try to avoid the use of Temporary Tables, try to use Table variables.
• Instead of LIKE search, Use Full Text Search for searching textual data 
• Try to use UNION to implement “OR” operation 
• Use VARCHAR(MAX), VARBINARY(MAX) and NVARCHAR(MAX) 
• Do not call functions repeatedly within your stored procedures, triggers, functions and batches.
• Try to avoid the use of triggers.
• Try to avoid nested transaction.
• Understanding the query execution plan
• Getting rid of the unnecessary Text column in the SELECT list
  

Apply advanced indexing and denormalization

• Apply some advanced indexing techniques
• Implement computed columns and create index on these
• Create "Indexed Views"
• Create indexes on User Defined Functions (UDF), using computed columns
• Create indexes on XML columns
  
• Apply de-normalizations, use history tables and pre-calculated columns

Diagnose database performance problems

• Diagnose performance problem, use SQL Profiler and Performance Monitoring tool effectively.
  

Optimize database files and apply partitioning

• Organize the file groups and files in the database
• Apply partitioning in the big fat tables
  

Original Source: M.M.Al-Farooque Shubho

Importance of CSS in web development

CSS style sheets have made it easier to handle web pages during web development. CSS or Cascading Style Sheets as the name suggests is a style sheet that allows you to easily link to other documents in your website. It allows you to retain control over the various elements in different web pages of your website.

CSS only defines the structure and content presentation of a website it has nothing to do with the design of a website. A single CSS sheet can control the font, positioning, colour and style information of an entire website.

9 advantages of using CSS
* Web pages are easier to load and uses less bandwidth
CSS style sheets are preferred by web developers for website development because they are lighter than table layouts, which consumes lots of bandwidth. The style sheet is downloaded only once and stored in the cache memory, so subsequent pages load faster.

* A CSS style sheet compliments well with HTML
HTML is insufficient when used independently in website development, but when combined with CSS they can result in technically stronger web pages.

* CSS allows you to position your element anywhere in the webpage
Web developers love to use CSS because it allows them to position their element where ever they want in the web page. If during any phase of web development the developer feels that particular links or columns are not going well with the situation then it becomes easier for them to position them easily using CSS. CSS reduces the risks associated with maintenance of the website.

* CSS is compatible with all web browsers
CSS is combined with HTML or XHTML by web developers for web application development because it is compatible with all web browsers. The sites that use CSS appear similar in all the web browsers.

* CSS can be used to create print friendly web pages
Most of the web developers love to use CSS for building their HTML based web applications because they allow them to create print friendly web pages. These web pages can be easily printed. The colours, images and other things which are difficult to be printed can be eliminated and printed easily.

* CSS style sheets allows the user to customize the webpage
Now days many websites allow the user to change the layout of the website without affecting the content. The CSS style sheets which are stored externally allow the user to make requisite changes by themselves. Most of the modern browsers give user the liberty to define their own style sheets like changing some font properties etc.

* CSS style sheets makes it easier for your website to feature in search engines
The CSS style sheets are favoured by web developers because they allow them to position their elements as per their wish anywhere in web application. Positioning helps to project the main contents first, so that it is easily captured by web spiders. CSS also gives cleaner HTML codes thus cutting down the job of web spider to search the real content from junk code.

* CSS allows the web pages to have absolute consistency
One of the reasons for using CSS during web development is that they allow consistency to all web pages. All the expressions and texts will get their characteristics from external style sheet. Web developers need not to worry about the change in characteristics of the elements because they can be easily altered at any stage of web development by using CSS.

* CSS lends portability to content
By using CSS you can make separate style sheets for different media. This provides you the great flexibility in presenting your content. CSS allows you to redefine the characteristics of elements in a website to suit the need of the situation. For e.g.: A separate style sheet will allow you to redefine the characteristics of certain elements so that they are easier to be printed. Also the user will never come to know that you had restructured the characteristics for their benefit.

CSS is created to make the things easier for your website and also to give you control over different elements in your website. Utilizing benefits of CSS will give you popular user friendly web pages.

To appreciate the beauty and flexibility of CSS, check out the site, CSSZenGarden.com
The Zen Garden aims to excite, inspire, and encourage participation. To begin, view some of the existing designs in the list. Clicking on any one will load the style sheet into this very page. The code remains the same, the only thing that has changed is the external .css file.

CSS allows complete and total control over the style of a hypertext document. The only way this can be illustrated in a way that gets people excited is by demonstrating what it can truly be, once the reins are placed in the hands of those able to create beauty from structure. To date, most examples of neat tricks and hacks have been demonstrated by structurists and coders. Designers have yet to make their mark. This needs to change.

Original Source:
http://support.fuchsiasoft.org/importance-of-css-in-web-development-t67.html

SQL Injection

SQL injection is a technique that exploits a security vulnerability occurring in the database layer of an application. The vulnerability is present when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and thereby unexpectedly executed. It is in fact an instance of a more general class of vulnerabilities that can occur whenever one programming or scripting language is embedded inside another.

SQL Injection: A Simple Example
Take a simple login page where a legitimate user would enter his username and password combination to enter a secure area to view his personal details or upload his comments in a forum.

When the legitimate user submits his details, an SQL query is generated from these details and submitted to the database for verification. If valid, the user is allowed access. In other words, the web application that controls the login page will communicate with the database through a series of planned commands so as to verify the username and password combination. On verification, the legitimate user is granted appropriate access.

Through SQL Injection, the hacker may input specifically crafted SQL commands with the intent of bypassing the login form barrier and seeing what lies behind it. This is only possible if the inputs are not properly sanitized (i.e., made invulnerable) and sent directly with the SQL query to the database. SQL Injection vulnerabilities provide the means for a hacker to communicate directly to the database.

The technologies vulnerable to this attack are dynamic script languages including ASP, ASP.NET, PHP, JSP, and CGI. All an attacker needs to perform an SQL Injection hacking attack is a web browser, knowledge of SQL queries and creative guess work to important table and field names. The sheer simplicity of SQL Injection has fueled its popularity.

Forms of SQL injection vulnerabilities
Incorrectly filtered escape characters
This form of SQL injection occurs when user input is not filtered for escape characters and is then passed into a SQL statement. This results in the potential manipulation of the statements performed on the database by the end user of the application.

Incorrect type handling
This form of SQL injection occurs when a user supplied field is not strongly typed or is not checked for type constraints. This could take place when a numeric field is to be used in a SQL statement, but the programmer makes no checks to validate that the user supplied input is numeric.

Blind SQL Injection
Blind SQL Injection is used when a web application is vulnerable to SQL injection but the results of the injection are not visible to the attacker. The page with the vulnerability may not be one that displays data but will display differently depending on the results of a logical statement injected into the legitimate SQL statement called for that page. This type of attack can become time-intensive because a new statement must be crafted for each byte recovered. A tool called Absinthe can automate these attacks once the location of the vulnerability and the target information has been established.

Preventing SQL Injection
To protect against SQL injection, user input must not directly be embedded in SQL statements. Instead, user input must be escaped, or parameterized statements must be used.

Using Parameterized Statements
Parameterized statements use parameters (sometimes called placeholders or bind variables) instead of embedding user input in the statement. In many cases, the SQL statement is fixed. The user input is then assigned (bound) to a parameter.

Enforcing the Use of Parameterized Statements
There are two ways to ensure an application is not vulnerable to SQL injection: using code reviews (which is a manual process), and enforcing the use of parameterized statements. Enforcing the use of parameterized statements means that SQL statements with embedded user input is rejected at runtime.

How to check for SQL injection vulnerabilities
Securing your website and web applications from SQL Injection involves a three-part process:

   1. Analysing the present state of security present by performing a thorough audit of your website and web applications for SQL Injection and other hacking vulnerabilities.
   2. Making sure that you use coding best practice sanitizing your web applications and all other components of your IT infrastructure.
   3. Regularly performing a web security audit after each change and addition to your web components.

Furthermore, the principles you need to keep in mind when checking for SQL Injection and all other hacking techniques are the following: “Which parts of a website we thought are secure are open to hack attacks?” and “what data can we throw at an application to cause it to perform something it shouldn’t do?”.

Checking for SQL Injection vulnerabilities involves auditing your website and web applications. Manual vulnerability auditing is complex and very time-consuming. It also demands a high-level of expertise and the ability to keep track of considerable volumes of code and of all the latest tricks of the hacker’s ‘trade’.

The best way to check whether your web site and applications are vulnerable to SQL injection attacks is by using an automated and heuristic web vulnerability scanner.

An automated web vulnerability scanner crawls your entire website and should automatically check for vulnerabilities to SQL Injection attacks. It will indicate which URLs/scripts are vulnerable to SQL injection so that you can immediately fix the code. Besides SQL injection vulnerabilities a web application scanner will also check for Cross site scripting and other web vulnerabilities.

Resources:

• http://en.wikipedia.org/wiki/SQL_injection
• http://www.unixwiz.net/techtips/sql-injection.html
• http://www.acunetix.com/websitesecurity/sql-injection.htm
• http://ferruh.mavituna.com/sql-injection-cheatsheet-oku/
• http://www.acunetix.com/websitesecurity/sql-injection2.htm