Do you cache or not? By default SQL Server cache stores the data & query plan in cache to provide better performance for your queries. Similary caching is also included in SQL Server Reporting Services where this caching can shorten the time required to retrieve a report if the report is large or accessed frequently. Bear in mind that If that server is rebooted, all cached instances are reinstated when the Report Server Web service comes back online that means all the cached reports will be disappeared....(
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Read the complete post at http://sqlserver-qa.net/blogs/tools/archive/2008/01/07/sql-server-reporting-services-do-you-cache-popular-reports-for-better-performance.aspx