What is a Listener?
The listener is used to listen to network requests to connect and pass them on to the instance. Any Remote connection to the database instance is made by the listener.
The single listener can connect to multiple instances, and a single instance can be connected by multiple listeners.
When the listener receives the client request, it selects one of the registered service handlers. Depending on the type of handler selected, the communication protocol used, and the operating system of the database server, the listener performs one of the following actions:
- Hands the connect request directly off to a dispatcher.
- Sends a redirect message back to the client with the location of the dispatcher or dedicated server process. The client then connects directly to the dispatcher or dedicated server process.
- Spawns a dedicated server process and passes the client connection to the dedicated server process.
After the listener has completed the connection operation for the client, the client communicates directly with the Oracle database without the listener’s involvement. The listener resumes listening for incoming network sessions.
The process in the 3 steps:
- 1. The client sends a connection request to the listener.
- 2. The listener parses the client request and forwards it to the service handler for the database service requested.
- 3. The client connects to the database.
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