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70-562 Caching




Caching is to improve performance, caching pages and framents, and also data can dramatically improve the performance of a website.

The only cachin in classic asp were variables, and it's usefullness was very limited.

Now, in asp.net, there are mutliple type of caching.

1)Caching pages and user controls by the OutputCache directive, for how long and how many version are kept
2)Caching from code, more control than by page, but only used if it needs to change at run time.
3)Caching data, data storage is always in process, dataset, arrays, custom objects, similar to store in sessions state, but application wide, can determine how long the object in cache, and the cache can be flushed when the memory gets low.

Retriving a page from the cache is much faster than regenrating the page.

Static pages need to be cached as they dont change, for pages that do change, mutliple versions can be kept.

As a simple tutorial, output the page directive and it's duration in seconds, VaryByParam allows to specify which version based on a value of the param, Common.GetOutputCacheDirective(Server.MapPath(pageFileName));

You can encode those params as query string, or form values, it's possible to use * for all the parameters on teh page, or many params sepecated by a semicolon-demilmited list.

If asp.net finds the right combination of params in the cache, it uses it, otherwise, builds the page.

The params can also be the IDs of the controls on the form.

The HTTP header can also be used to identify page variations. VaryByHeader="Referer" in the page directive allows to vary by the caller(the calling page).

VAryByCustom can be used to vary by browser. In the global asax it's possible to override the GetVAryByCustomString value, which can be used for testing browser versions.

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