|Concepts and Planning||<<||>>|
A user action is an action, such as opening a mailbox, that the user performs on the client. The server performs actions in response to such a user action. From the user's point of view, these actions are synchronous. For example, opening an unread message in a mailbox on the server entails processing time for the server to receive and interpret the request and to evaluate any access restrictions. This happens in the time it takes for the remote procedure call (RPC) issued by the client application to return control to the client. The time the user perceives the operation to take is this time plus any additional processing time needed by the client application to draw the message window and perform other tasks.
When users interact with the server directly, their actions place an immediate incremental load on the server. User actions are the most significant load factor on servers that directly support users (as opposed to backbone or connector servers). For any given server, the load created by user actions is proportional to the number of users actively interacting with the server and the actions they perform.