Every Virtual User that Silk Performer simulates, creates a new SAP client application. Each of these SAP client applications creates a new connection to the SAP server. To create a new connection the SAP Client first needs to create a new window. Each window created will use resources from the operating system Graphical Device Interface (GDI). When an agent machine runs out of GDI resources the newly created SAP client application cannot create a window and the connection fails. Silk Performer is simply reporting that the SAP GUI could not create a new connection to the SAP server. This is a limitation of both the SAP GUI, which is not designed to operate in parallel and the Operating System which has limited resources available for the GDI. A Silk Performer agent installed on a Windows 2000 or XP machine with a 1GHZ Processor and 1GB of RAM should be able to handle approximately 50-70 virtual users executing during a loadtest. Windows 2003 Server has better management of the GDI resources and this should allow approximately 30% more VU"s to to be executed. In practice a windows 2003 Server with 8 x 1GHz CPU and 4Gig of RAM we have seen 200 VU"s running on an agent machine. Old KB# 17950
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