Caching

Cached data is data that has been duplicated or stored somewhere for quick access without the need to re-fetch or recalculate it every time it is requested. When caching is enabled website performance can be greatly enhanced.

 

There are three types of caching available in MOSS, each described below.

 

Disk based caching is used to store large files (also known as Binary Large Objects (BLOBs)) such as images, css files and multimedia files on the file system on a web server. When this form of caching is enabled on a MOSS website, large files are retrieved from the content database on its first request and then future requests are served from the file system, eliminating the need to make a call to the database every time the data is required. All data is still security trimmed by MOSS upon retrieval.

 

Disk Basd Caching is not enabled by default but turning it on is easy. Just open the web.config file and search for 'blobcache'. Change the enabled field to false and either accept the default maximum age of the cache (24 hours) or alter it using the max-age tag. You can also add to the list of file types that are cached and if a second hard drive is available it is recommended to change the cache storage location to point to that drive.

 

For more information on Disk Based Caching and how to enable it, see this msdn article: http://msdn2.microsoft.com/en-us/library/aa604896.aspx

 

 

Object Caching is the only type of caching that is enabled by default. It is used to cache items on a web page such as navigation data and cross list query results (from a content query web part). This type of caching greatly enhances performance of heavy web pages that may be bogged down with several content query web parts. While it is on by default you should still update its configuration to suit your environment. By default the cache is limited to 100MB and cross list query results are only cached for 90 seconds. These settings can be reconfigured using the browser interface at the Site Collection level. Just go to Site Actions-->Site Settings-->Modify All Site Settings and under Site Collection Administration select Site Collection Object Cache.

 

For more information on Object Caching see this msdn article: http://msdn2.microsoft.com/en-us/library/aa622758.aspx 

 

 

Output Caching is used to cache individual pages in the server's memory so that once a user accesses a page that same copy of it is then served to additional users for the duration of the cache. You can specify the duration that a page exists in the cache without being recalculated and the duration can differ based on authentication. It is common to have pages stay cached for longer durations for anonymous users, but shorter durations for authenticated users who may be performing content updates and need to see the changes sooner.

 

The duration and other settings such as the need to perform a security check are specified in MOSS in Cache Profiles. All of these settings are accessible through the browser interface under Site Actions-->Site Settings-->Modify All Site Settings-->Site Collection Administration-->Site Collection Output Cache and Site Collection Cache Profiles. Note that when this type of caching is enabled, it is recommended to check the box allowing different page layouts to use different cache profiles. Then modify the searchresults page layout so that it does not perform caching. This ensures that search results are always security trimmed.

 

For more information on Output Caching see this msdn article: http://msdn2.microsoft.com/en-us/library/aa661294.aspx