Understanding SQL*Net

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How SQL*Net Establishes Connections to a Multi-Threaded Server

The multi-threaded server enables many clients to connect to the same server without the need for dedicated server processes for each client. Using the multi-threaded server enables you to minimize the memory and processing resources needed on the server side as the number of connections to the database increases.

The sequence of events that occurs with the Oracle7 multi-threaded server is as follows:

What Happens When an MTS and Listener Are Started

During initial startup of the Oracle7 multi-threaded server and the listener, the following sequence occurs:

Note: A wildcard listen is where the server process listens, but informs the underlying protocol stack (or operating system in the case of the IPC Protocol Adapter) that it has no preference as to what address it listens for other than specifying the protocol on which it wishes to perform the operation. As a result, many operating systems will choose a free listening address and automatically assign this to the requesting server process.

Note: If step 2 is performed before step 1, the dispatchers will be unable to contact the listener in step 3. If this occurs, each dispatcher loops and attempts to reconnect to the listener every 60 seconds. Meanwhile, incoming connection requests will be handled through other means (prespawned dedicated or newly spawned dedicated server processes).

The listener and the Oracle7 multi-threaded server should be ready for incoming connections at this point. You can check which dispatchers have registered with the listener by typing

lsnrctl services listener_name 

How a Multi-Threaded Server Connection Request Is Handled

The following is how a multi-threaded server connection request is handled:

When an Oracle7 Server has been configured as a multi-threaded server, incoming connections are always routed to the dispatcher unless the connection request specifically requests a dedicated server (by having SERVER=DEDICATED in the CONNECT_DATA portion of the connect descriptor) or no dispatchers are available. To create this parameter, create an alias for the database using Network Manager. (An alias is an alternative name that is mapped to a service name.) Use Network Manager to make that alias a dedicated server. See Chapter 5 in the Oracle Network Manager Administrator's Guide for more information.


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