23 June, 2008

Performance Tips for ASP.NET Applications

Cache Aggressively
When designing an app using ASP.NET, make sure you design with an eye on caching. On server versions of the OS, you have a lot of options for tweaking the use of caches on the server and client side. There are several features and tools in ASP that you can make use of to gain performance.
Output Caching—Stores the static result of an ASP request. Specified using the @% OutputCache % directive:
  • Duration—Time item exists in the cache
  • VaryByParam—Varies cache entries by Get/Post params
  • VaryByHeader—Varies cache entries by Http header
  • VaryByCustom—Varies cache entries by browser
  • Override to vary by whatever you want

Fragment Caching—When it is not possible to store an entire page (privacy, personalization, dynamic content), you can use fragment caching to store parts of it for quicker retrieval later.
a) VaryByControl—Varies the cached items by values of a control.

Cache API—Provides extremely fine granularity for caching by keeping a hashtable of cached objects in memory (System.web.UI.caching). It also:

  • Includes Dependencies (key, file, time)
  • Automatically expires unused items
  • Supports Callbacks

Caching intelligently can give you excellent performance, and it's important to think about what kind of caching you need. Imagine a complex e-commerce site with several static pages for login, and then a slew of dynamically-generated pages containing images and text. You might want to use Output Caching for those login pages, and then Fragment Caching for the dynamic pages. A toolbar, for example, could be cached as a fragment. For even better performance, you could cache commonly used images and boilerplate text that appear frequently on the site using the Cache API.

Use Session State Only If You Need To

One extremely powerful feature of ASP.NET is its ability to store session state for users, such as a shopping cart on an e-commerce site or a browser history. Since this is on by default, you pay the cost in memory even if you don't use it. If you're not using Session State, turn it off and save yourself the overhead by adding @% EnabledSessionState = false % to your asp.

For pages that only read session state, you can choose EnabledSessionState=readonly. This carries less overhead than full read/write session state, and is useful when you need only part of the functionality and don't want to pay for the write capabilities.

Use View State Only If You Need To

An example of View State might be a long form that users must fill out: if they click Back in their browser and then return, the form will remain filled. When this functionality isn't used, this state eats up memory and performance. Perhaps the largest performance drain here is that a round-trip signal must be sent across the network each time the page is loaded to update and verify the cache. Since it is on by default, you will need to specify that you do not want to use View State with @% EnabledViewState = false %.

Batch Compile

Always batch compile before deploying a large page into the Web. This can be initiated by doing one request to a page per directory and waiting until the CPU idles again. This prevents the Web server from being bogged down with compilations while also trying to serve out pages.

Avoid the Autoeventwireup Feature

Instead of relying on autoeventwireup, override the events from Page. For example, instead of writing a Page_Load() method, try overloading the public void OnLoad() method. This allows the run time from having to do a CreateDelegate() for every page.

protected override void OnLoad(EventArgs e)
Response.Write("Page Load method Over ridden");

Use the Optimal Authentication Procedure

There are several different ways to authenticate a user and some of more expensive than others (in order of increasing cost: None, Windows, Forms, Passport). Make sure you use the cheapest one that best fits your needs.

Use Stored Procedures Whenever Possible

Stored procedures are highly optimized tools that result in excellent performance when used effectively. Set up stored procedures to handle inserts, updates, and deletes with the data adapter. Stored procedures do not have to be interpreted, compiled or even transmitted from the client, and cut down on both network traffic and server overhead. Be sure to use CommandType.StoredProcedure instead of CommandType.Text

Use StringBuilder for Complex String Manipulation

When a string is modified, the run time will create a new string and return it, leaving the original to be garbage collected. Most of the time this is a fast and simple way to do it, but when a string is being modified repeatedly it begins to be a burden on performance: all of those allocations eventually get expensive.

Minimize the Use of Format()

When you can, use toString() instead of format(). In most cases, it will provide you with the functionality you need, with much less overhead.

Optimize Assignments

Use exp += val instead of exp = exp + val. Since exp can be arbitrarily complex, this can result in lots of unnecessary work. This forces the JIT to evaluate both copies of exp, and many times this is not needed. The first statement can be optimized far better than the second, since the JIT can avoid evaluating the exp twice.

Keep Your Datasets Lean

Only put the records you need into the dataset. Remember that the dataset stores all of its data in memory, and that the more data you request, the longer it will take to transmit across the wire.

Limit ASP.NET Server Controls

Exceptions and session state impose overhead. Surprise—so do ASP.NET server controls. They require server-side support, which leads to communication between your server and the client to support the control, and resource consumption on the server. Avoid the temptation to drop the server control onto your form and forget about it. In fact, you might be better off with a regular HTML control. Use the server control only if you plan to control the properties of a control programmatically, use view state to hold data values of the control, or handle server-side events generated by the control.

Use Page.IsPostBack

You need to take a series of steps when your page loads for the first time to perform setup formatting on the page or initialize data. However, you don't need to keep reinventing this wheel the next time a page is requested—and the next and the next. Avoid initializing the data again on the postback.

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