Overview of SQL*Net, Net8, and Connection Manager

SQL*Net handles all the networking and connectivity issues for the Oracle environment. Oracle has always had a background process started on the server for each connecting process on the server or by a networked user (see Figure 19.2). There has also always been a listener process (it used to be called ORASRV) that ran on each server, monitoring SQL*Net traffic for Oracle databases on that particular server. This listener process used to start the background process (a resource-intensive process), establish connectivity between the connecting process and the background process, and then go back to a wait state until the next new connection was requested. Oracle7 introduced the concept of a multithreaded server (MTS), where a dispatcher (or several dispatchers) was established to take over the SQL*Net traffic once communications from a connected process were established. Multithreaded servers’ primary purpose is to allow for the sharing of these background processes. Depending on the application, a dispatcher can allow ten users to share a single background process. With the dispatcher assigning background server processes to connecting processes, it is now possible to monitor and prestart several of the background processes ahead of time to eliminate the overhead and end-user wait time typically associated with connecting to the Oracle database. The dispatcher will assign incoming connections to the background processes in its control. If all of the background processes are in use, the dispatcher will start another background process on the connection’s behalf, just as it used to do. This architecture is what Oracle refers to as the multithreaded server. There can be as many dispatchers as needed to handle the SQL*Net traffic. Memory management and machine resources are more efficient because the prestarted background processes are not being constantly terminated and started as connections to the database are established and disconnected. There is at least one listener (with its own dispatcher or set of dispatchers and prestarted background processes) per network protocol (TCP/IP, Dec NET, SPX/IPX, and so on). The listener will load-balance the SQL*Net traffic among the assigned dispatchers (see Figure 19.2).

Figure 19.2.  A typical SQL*Net environment.

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Note:  
Shops with a high volume of SQL*Net traffic often have more than one listener running per Oracle instance.

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Net8 builds on where SQL*Net leaves off. The Connection Manager process acts as a concentrator for the MTS environment only (see Figure 19.3). This concentrator feature can handle traffic from multiple separate connections by combining the various connections (regardless of network protocol) into one physical link to the dispatchers. SQL*Net has a separate process called a MultiProtocol Interchange that will convert the SQL*Net traffic from one network protocol to another, kind of like a bridge. Connection Manager eliminates the need for this separate function. Connection Manager can also act as a firewall, allowing only authorized connections, and the connections can be based on source, host name, and the Oracle database desired.

Figure 19.3.  Net8 and Connection Manager.

Net8 has also enhanced the listener process. The listener has been enhanced to load- balance among participating servers. It supports the traditional two-tier configuration (client/server) and also supports the N-tier configuration, a disconnected environment using a distributed message queue process.

Security and authentication have been significantly improved via the Oracle Security Server. Security Server can do single sign-on, can handle the concept of a global user (with global rules), and supports multiple authentication methods. Security Server comes with a tool kit (a set of APIs) to extend this level of security to applications such as email and electronic commerce.

Net8 also has improved the Name Services. SQL*Net has a Names Server to resolve names to locations. This method of naming makes it very easy to move Oracle servers and databases with no impact on the end-user community. The Net8 Name Services has the ability to cache names at the client for much faster resolution, and the various listeners and connection managers register as available with Name Services.