5.5 Understanding Database Server Process Architecture

Based on the service handler type registered with the listener, the listener forwards requests to either a shared server or dedicated server process. The shared server architecture enables a database server to allow many client processes to share server processes. In a dedicated server configuration, the listener starts a separate dedicated server process for each incoming client connection request dedicated to servicing the client.

• About Shared Server Processes
  
• About Dedicated Server Processes
  

5.5.1 About Shared Server Processes

Shared server processes are used in the shared server architecture, as shown in Figure 5-4. With shared server architectures, client processes ultimately connect to a dispatcher. The LREG process registers the location and load of the dispatchers with the listener, enabling the listener to forward requests to the least loaded dispatcher. This registration process is not shown in the figure.

A dispatcher can support multiple client connections concurrently. Each client connection is bound to a virtual circuit. A virtual circuit is a piece of shared memory used by the dispatcher for client database connection requests and replies. The dispatcher places a virtual circuit on a common request queue when a request arrives. An idle shared server picks up the virtual circuit from the request queue, services the request, and relinquishes the virtual circuit before attempting to retrieve another virtual circuit from the request queue. Shared servers place all completed requests into a dispatcher's response queue. Each dispatcher has its own response queue in the SGA (System Global Area). This approach enables a small pool of server processes to serve a large number of clients.

Figure 5-4 Shared Server Architecture

Description of "Figure 5-4 Shared Server Architecture"

5.5.2 About Dedicated Server Processes

In a dedicated server architecture, each client process connects to a dedicated server process. The server process is not shared by any other client. Figure 5-5 illustrates a dedicated server architecture.

LREG registers information about dedicated server processes with the listener. This enables the listener to start a dedicated server process when a client request arrives and forward the request to it.

Note:

Dedicated server architectures do not support HTTP, FTP, or WebDAV clients. Only database clients are supported.

Figure 5-5 Dedicated Server Architecture

Description of "Figure 5-5 Dedicated Server Architecture"