SQL Server - What is cash dependency?

Guess you are referring to Cache Dependency. Find more info about creating and adding a SQL Server 2005 Cache Dependency here - http://www.devx.com/dotnet/Article/27865/0/page/7

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In brief, a cache dependency represents a logical dependency between a cached item and a file(s), folder(s), or another cached item(s). When the dependency is broken (i.e., the file/folder/item changes), the bound cached item is removed from the cache.

Caching has long been recognized as one of the more effective ways to improve your ASP.NET web applications.In ASP.NET 2.0, Microsoft has  added the new SQL cache dependency feature.

To illustrate SQL cache dependency in ASP.NET 2.0 visit.These links will give you enough information as well as code also

http://www.ondotnet.com/pub/a/dotnet/2005/01/17/sqlcachedependency.html

http://www.eggheadcafe.com/articles/20030716.asp    

http://aspnetresources.com/blog/sql_cache_depedency_overview.aspx

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See these articles to see cache dependency in sql server

http://www.wrox.com/WileyCDA/Section/Using-the-ASP-NET-2-0-SQL-Server-Cache-Dependency.id-306459.html

http://www.codeproject.com/KB/web-cache/CachingDependencies.aspx

http://www.eggheadcafe.com/articles/20030716.asp

http://quickstarts.asp.net/QuickStartv20/aspnet/doc/caching/SQLInvalidation.aspx

Hope it helps.