Page 2 - Best Practices : ASP Coding, SQL Statements, and Database Structuring

Variable Value Trimming

Be consistent when trimming values. Trim numeric values to the desired length before putting them in state. This will eliminate errors in processing caused by inconsistencies in trimming schemes. For example, a value such as 9.997 used repeatedly as a multiplier would accumulate a different result than the trimmed value 9.9. Trim unneeded leading and trailing spaces from strings by using LTrim, RTrim, or Trim, to eliminate the possibility of a space causing a processing error or a display misalignment.

Object and Variable Initialization

The following information will help you to initialize and set dimensions for objects and variables, in order to achieve faster execution and efficient use of server resources. Unless stated otherwise, VBScript is assumed.


Scoping Variables

Using Page Scope for Best Performance


Local variables reside within functions and subroutines. Give page scope (also called local scope) to variables unless you have a compelling reason to use a broader scope. For example, you might want to assign session scope to a variable that is used in more than one script in a user session. Local variables are compiled into table entries. At run time, references to local variables are resolved with fast-executing table lookups, giving local variables faster performance than global variables.


Using Global Variables Sparingly and Efficiently


Global variables are resolved at run time, and execute much more slowly than local variables. An undeclared global variable is the slowest, requiring a search of the entire variable list the first time it is used. When you need to give global scope to variables, declare them using the Dim statement before using them. This saves valuable time on first use by eliminating a search of the entire variable list.


Avoiding the Use of Public Variables


Do not use variables defined as Public. The Public keyword is under review to determine future use. Use Dim instead.


Using Application Scope for Objects

Information stored in variables with application-wide scope is in memory and is cached for access by any page in the application. Give application scope to variables used often within an application, if the values do not change frequently.


Whatever the potential benefits, use caution in deciding whether or not to give application scope to an object. It can potentially affect performance and decrease reliability (your application could stop responding). To get the best performance using objects with application scope, set threading at BOTH.



Avoiding the Use of Server Variables

It is a best practice to avoid using server variables if your application does not need them. Whenever your ASP application accesses a server variable, your Web site makes a request that retrieves the server's entire variable collection—not just the variable to be used. This causes a performance hit the first time a server variable is used. You can enforce this restriction by setting the ENABLESESSIONSTATE directive to FALSE.

Using the ENABLESESSIONSTATE directive (set in Internet Services Manager) for your site enables the detailed tracking of user requests.

In order to save those resources that IIS uses to process scripts for pages not using session state information, set the ENABLESESSIONSTATE directive to FALSE for those pages:

<%@ ENABLESESSIONSTATE=False %>


Declaring Objects with the <OBJECT> Tag

For objects that may or may not be used in an application, it's often most efficient to declare the objects without creating them.

Do not use scripts in ASP pages in order to perform tasks that are readily accomplished by browser scripts, since ASP consumes server resources. By scripting the browser to perform tasks such as data validation, calculations, and selection of simple conditional output, you can save server resources for those tasks actually requiring ASP. For example, you could use a client-side script in order to validate the input data and to calculate monthly payments for a user who enters a loan amount and specifies the length of the repayment cycle.

To make the most efficient use of your server resources, use the .asp file name extension for pages that contain scripts or that are likely to need scripting in the future. Use the .htm extension for pages that will contain just HTML statements as well as scripts interpreted by the browser.

The VBScript Dictionary object enables fast lookup of arbitrary key/data pairs. Because the Dictionary object gives you access to array items by key, it is fast for finding items that are not in contiguous memory, since you are specifying a key, rather than knowing where in the array the item is located.

Use the Dictionary object when you have set a high priority on fast searches of nonlinear data.

Busy data servers cause slowdowns in ASP database applications that request database connections. Use the ConnectionTimeout property of the Connection object. This limits the time your application has to wait in order for a connection request to complete.

Browser users often request an ASP page, then move on before the requested page has finished processing. Use the Response.IsClientConnected property to determine the connection status of the target browser. If the target browser is no longer connected, cut off ASP page processing to avoid wasting server resources.

If the user gets impatient, he or she may abandon your ASP page before you even start executing their request. If he clicks Refresh or moves to a different page on your server, you will have a new request sitting at the end of the ASP request queue and a disconnected request sitting in the middle of the queue. Often this happens when your server is under high load (so it has a long request queue, with correspondingly high response times) and this only makes the situation worse. There's no point executing an ASP page (especially a slow, heavyweight ASP page) if the user is no longer connected. You can check for this condition by using the Response.IsClientConnected property. If it returns False, you should call Response.End and abandon the rest of the page. In fact, IIS 5.0 codifies this practice—whenever ASP is about to execute a new request, it checks to see how long the request has been in the queue. If it has been there for more than 3 seconds, ASP will check to see if the client is still connected and immediately terminate the request if it's not. You can use the AspQueueConnectionTestTime setting in the metabase to adjust this timeout of 3 seconds.

If you have a page that takes a very long time to execute, you may also want to check Response.IsClientConnected at intervals. When response buffering is enabled, it is a good idea to do Response.Flush at intervals to give the user the impression that something is happening.

Note On IIS 4.0, Response.IsClientConnected will not work correctly unless you first do a Response.Write. If buffering is enabled, you'll also need to do a Response.Flush. On IIS 5.0, there is no need for this—Response.IsClientConnected works fine. In any case, Response.IsClientConnected has some costs, so only use it before an operation that takes at least, say 500 milliseconds (that's a long time if you're trying to sustain a throughput of dozens of pages per second). As a general rule of thumb, don't call it in every iteration of a tight loop, such as when painting the rows of a table—perhaps every 20th or 50th row of the table, instead.


example:

Using a model /directory structure will help you establish consistency, security, and ease of maintenance.

[Root Dir]--Application_Name
The application root directory name should clearly convey the theme of the site. For example, an application for financial research might be named /Financial_Research. Avoid application root names that might be misidentified as standard subdirectories of a site, such as /Media or /Content. Also, avoid names that read like part numbers or codes, such as /FR98346A.To avoid adversely affecting production sites, develop the application in a development test environment. An easy way to do this is to develop new applications under the IIS HTTP root directory, /InetPub/wwwroot, then move them to the same directory under /InetPub/wwwroot in the production environment when they are ready.The root directory of every application should contain at least these files
--Default.htm
--Global.asa
The file Global.asa specifies event scripts, declares objects that have application or session scope, and
declares type libraries. For example, Global.asa scripts make application- and session-scope variables
available at startup. Global.asa must be stored in the application root directory

/Classes
Classes directory holds Java classes used by the application

/Content
The /Content directory holds all pages (except Default.htm) and media that might be retrieved by a user
of the site.

/ASP
The /ASP subdirectory of /Content contains all pages with server-side scripting. This directory must
contain execute permissions so that ASP can execute the page scripts; storing all scripted pages here
simplifies permissions management and site security.

/HTM
The /HTM subdirectory of /Content holds all pages containing only standard HTML. This directory is read-
only and does not have execute permissions. A page containing server-side scripts that is stored here will
not execute.

/Images
The /Images subdirectory of /Content contains graphics that are used independently of theme-related
images, such as standard buttons and icons.

/Media
The /Media subdirectory of /Content contains subdirectories for audio, images, animation files, .avi files,
and similar items used throughout the application

/Themes
The /Themes subdirectory of /Content is used in order to enable application-wide changes to the look of a
site. The subdirectory contains style sheets, bullets, buttons, icons, rules, and similar items, and should be
organized so that you can easily change the look of an application by modifying any or all the theme-
related items. Each item in the /Themes subdirectory can be linked dynamically by setting an application
variable to its virtual path.

/Data (not in site directory)
The /Data directory contains all database access information such as SQL scripts, file*based dataset names
or similar data needed by the application. Do not place this directory under the site directory, as this could
enable an unauthorized user to access business rules and private data.

/DLLs (not in site directory)
The /DLLs directory contains Microsoft® Component Object Model (COM) components and Microsoft®
Visual Basic® 6.0 run-time DLLs, such as Vbrun500.dll and Msvbvm50.dll. Do not place this directory under
the site directory, as this could enable an unauthorized user to access business rules and private data.

/Helper_Files
Helper files are server-side include files or text files that make HTML-coded information available across the
application. For security reasons, the directory containing helper files should not be stored in the published
Web space (the Web site directories identifiable to users).

Slow: (one per line)


A little faster (de-reference the object) :


Faster: (Concatenate strings)


Faster Still (Use continuation character):


Even Faster (all on one line):

nice thread, fit for sticky in my opinion. keep up the good job!!

Use meaningful variable names to clearly show what type of data the variable should hold:

I posted a thread a while ago with sample code about Database connection strings using the global.asa file. Click here to see the thread.

Good work bslintx! I enjoy trawling through this thread.

hmm... can I post this message?

Use proper Hungarian notation for variables and objects. The purpose of Hungarian notation is to be able to interpret the type and purpose of a variable. For local and public variables use mixed case of an initial lowercase Hungarian prefix followed by at least one uppercase letter

Hungarian table examples: