ASP Tips: Tip 1: Cache Frequently-Used Data on the Web Server

Performance is a feature. You need to design for performance up front, or you get to rewrite your application later on. That said, what are some good strategies for maximizing the performance of your Active Server Pages (ASP) application?

This article presents tips for optimizing ASP applications and Visual Basic® Scripting Edition (VBScript). Many traps and pitfalls are discussed. The suggestions listed in this article have been tested on http://www.microsoft.com and other sites, and work very well. This article assumes that you have a basic understanding of ASP development, including VBScript and/or JScript, ASP Applications, ASP Sessions, and the other ASP intrinsic objects (Request, Response, and Server).

Often, ASP performance depends on much more than the ASP code itself. Rather than cover all wisdom in one article, we list performance-related resources at the end. These links cover both ASP and non-ASP topics, including ActiveX® Data Objects (ADO), Component Object Model (COM), databases, and Internet Information Server (IIS) configuration. These are some of our favorite links-be sure to give them a look.

Tip 1: Cache Frequently-Used Data on the Web Server

A typical ASP page retrieves data from a back-end data store, then paints the results into Hypertext Markup Language (HTML). Regardless of the speed of your database, retrieving data from memory is a lot faster than retrieving data from a back-end data store. Reading data from a local hard disk is also usually faster than retrieving data from a database. Therefore, you can usually increase performance by caching data on the Web server, either in memory or on disk.

Caching is a classic space-for-time tradeoff. If you cache the right stuff, you can see impressive boosts in performance. For a cache to be effective, it must hold data that is reused frequently, and that data must be (moderately) expensive to recompute. A cache full of stale data is a waste of memory.

Data that does not change frequently makes good candidates for caching, because you don't have to worry about synchronizing the data with the database over time. Combo-box lists, reference tables, DHTML scraps, Extensible Markup Language (XML) strings, menu items, and site configuration variables (including data source names (DSNs), Internet Protocol (IP) addresses, and Web paths) are good candidates for caching. Note that you can cache the presentation of data rather than the data itself. If an ASP page changes infrequently and is expensive to cache (for example, your entire product catalog), consider pregenerating the HTML, rather than repainting it for every request.