When the number of concurrent users increases in Microsoft SQL Server 2008 R2 Analysis Services (SSAS 2008 R2), the execution time of each discover MDSCHEMA_CUBES request increases. You may experience poor performance in SSAS 2008 R2.
The issue was first fixed in the following cumulative update of SQL Server.
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server: