Friday, February 18, 2011

Response Buffering

You can buffer a whole page worth of output by turning on "response buffering." This minimizes the amount of writes to the browser and thus improves overall performance. Each write has a lot of overhead (both in IIS and in the amount of data sent down the wire), so the fewer the writes there are, the better. TCP/IP works much more efficiently when it can send a few large blocks of data than when it has to send many small blocks because of its slow start and Nagling algorithms (used to minimize network congestion).

There are two ways of turning response buffering on. First, you can turn on response buffering for an entire application, using the Internet Services Manager. This is the recommended approach and response buffering is turned on by default for new ASP applications in IIS 4.0 and IIS 5.0. Second, on a page-by-page basis, you can enable response buffering by placing the following line of code near the top of the ASP page:

<% Response.Buffer = True %>

This line of code must be executed before any response data has been written to the browser (that is, before any HTML appears in the ASP script and before any Cookies have been set using the Response.Cookies collection). In general, it is best to turn response buffering on for an entire Application. This allows you to avoid the above line of code on every page.

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