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Developing AppServer Applications
AppServer and Client Interaction : Understanding AppServer operating modes

Understanding AppServer operating modes

The basis of AppServer support for client interaction is the AppServer operating mode, which determines how client requests can be processed by the AppServer. The AppServer supports any one of four possible operating modes. Depending on the operating mode, the interaction between the AppServer and client conforms to one of two possible session models:
*Session-managed — Where a single AppServer handles all requests from a single client to a single application service, and the client manages a physical connection to the AppServer
*Session-free — Where one or more AppServers can handle all requests from a single client to a single application service, and the client manages no physical connection to any single AppServer
Regardless of the operating mode, a client can invoke synchronous or asynchronous requests to the AppServer, which the client manages depending on the session model.
When you configure an AppServer, you specify an operating mode that indicates how the AppServer broker manages its AppServer agent pool and assigns client requests to AppServer agents within the pool. The choice of operating mode has a potentially major affect on the performance and design of your AppServer application, including both the procedures that run on the AppServer and your client application.
Any ABL procedure running on the AppServer can determine the operating mode it is running on by reading the value of the SERVER-OPERATING-MODE attribute on the SESSION system handle. This is a CHARACTER parameter that returns the name of the operating mode as a string:
The sections that follow describe these operating modes in detail.
For information on the AppServer architecture and an overview of AppServer operating modes, see OpenEdge Getting Started: Application and Integration Services. For information on how to configure the operating mode for an AppServer instance, see OpenEdge Application Server: Administration.
* State-reset operating mode
* State-aware operating mode
* Stateless operating mode
* State-free operating mode