Why listener in oracle

Each listener is configured with one or more protocol addresses that specify its listening endpoints. The listener agent dynamically updates endpoints with the listener. Starting with Oracle Database 11 g Release 2, the listener. Listening endpoints, such as the port numbers, are dynamically registered with the listener.

Oracle Net Listener is a separate process that runs on the database server computer. It receives incoming client connection requests and manages the traffic of these requests to the database server. This chapter describes how to configure the listener to accept client connections.

Chapter 2, "Identifying and Accessing the Database" for a description of how the listener is used during an initial connection request. Chapter 4, "Understanding the Communication Layers" for an architectural overview of the listener. A listener is configured with one or more listening protocol addresses, information about supported services, and parameters that control its run-time behavior. The listener configuration is stored in a configuration file named listener. Because all of the configuration parameters have default values, it is possible to start and use a listener with no configuration.

The listener forwards client requests to supported services. These services can be configured statically in the listener. This dynamic registration feature is called service registration.

The registration is performed by the PMON process , an instance background process of each database instance that is configured in the database initialization parameter file. Dynamic service registration does not require any manual configuration in the listener. Because the listener always monitors the state of the instances, service registration facilitates automatic failover of a client connect request to a different instance if one instance is down.

Service registration enables the listener to forward client connect requests to the least-loaded instance and dispatcher or dedicated server. Service registration balances the load across the service handler s and nodes.

Oracle Net Configuration Assistant configures the listening protocol address and service information for Oracle Database. During a Custom installation, Oracle Net Configuration Assistant prompts for the listener name and protocol address. A listening IPC protocol address for external procedure calls is automatically configured, regardless of the installation type.

Oracle Net Configuration Assistant also automatically configures service information for the external procedures in the listener. If you are using the IPC protocol, then you can improve performance by specifying the maximum number of concurrent IPC connection requests to match your expected connection requests.

Example shows a sample listener. If the default or installed configuration is not adequate for a particular environment, then you can use Oracle Net Manager to customize the listener. Oracle Enterprise Manager and Oracle Net Manager can be used to configure protocol support for the listener.

This technique can create listening endpoints that service IPv6 clients. To configure protocol addresses for the listener using Oracle Enterprise Manager, do the following:. In the navigator pane, expand Local , and then select Listeners. If you want to set send and receive buffer sizes, then click Show Advanced , and then enter the sizes in the appropriate fields. Select Save Network Configuration from the File menu to save the changes.

The listener uses the dynamic service information about the database and instance before using statically configured information in the listener. Configuration of static service information is necessary if you require remote database startup from a tool other than Oracle Enterprise Manager, or you have Oracle Database releases earlier than Oracle8 i. Table describes static service settings in the listener.

Table Static Service Settings in listener. The Oracle system identifier SID of the instance. If the client connect descriptor uses the SID parameter, then the listener does not attempt to map the values. This parameter is primarily intended for configurations with Oracle8 databases where dynamic service registration is not supported for dedicated servers.

This parameter may also be required for use with Oracle8 i and later database services by some configurations. The Oracle home location of the instance. Without this setting, the listener assumes its Oracle home for the instance. On Microsoft Windows, this setting is ignored. Select Listeners from the Administer list, and then select the Oracle home that contains the configuration files.

Click the Static Database Registration tab, and then click Add. The following example shows an excerpt of a listener. Chapter 13, "Enabling Advanced Features of Oracle Net Services" for additional information about statically configuring the listener for external procedures and Heterogeneous Services. By default, Oracle Net Listener permits only local administration for security reasons.

As a policy, the listener can be administered only by the user who started it. Table for a description of the fields. For example, an excerpt of a listener. It is important to provide security through a password for the listener. With a password, privileged operations, such as saving configuration changes or stopping the listener, used from the Listener Control utility will require a password.

If the unencrypted password is not removed, you will be unable to successfully set an encrypted password. Dynamic service registration is configured in the database initialization file.

It does not require any configuration in the listener. However, listener configuration must be synchronized with the information in the database initialization file. This section contains the following configuration topics related to service registration:. To ensure service registration works properly, the initialization parameter file should contain the following parameters:. As long as the listener configuration is synchronized with the database configuration, PMON can register service information with a nondefault local listener or a remote listener on another node.

Synchronization is simply a matter of specifying the protocol address of the listener in the listener. You can then resolve listener1 in the local tnsnames. Registration to remote listeners, such as in the case of Oracle9 i Real Application Clusters, can be configured for shared server or dedicated server environments. If you set the parameter to null with the statement that follows, then PMON de-registers information with the remote listener with which it had previously registered information.

Oracle Net Manager does not enable you to configure a tnsnames. Therefore, Oracle Corporation recommends that you manually modify the tnsnames. Multiple addresses are supported, but connect-time failover and client load balancing features are not supported. Chapter 15, "Enabling Advanced Features of Oracle Net Services" for further information about multiple address configuration.

An entry for the listener alias name can be made to an Oracle Names server through Oracle Net Manager:. Once the listener is configured, the listener can be administered with the Listener Control utility. This section describes some of the common administrative tasks for the listener, including the following topics:.

In addition to starting the listener, the Listener Control utility verifies connectivity to the listener. The STATUS command provides basic status information about a listener, including a summary of listener configuration settings, the listening protocol addresses, and a summary of services registered with the listener. You can also obtain the status of a listener through the Oracle Enterprise Manager Console. Displays a summary of the services registered with the listener and the service handlers allocated to each service.

To connect to a database service, clients first contact a listener process that typically resides on the database server. The listener receives incoming client connection requests and sends these requests to the database server. After the connection is established, the client and database server communicate directly.

The listener knows which services can handle connection requests because an Oracle database dynamically registers this information with the listener. This process of registration is called service registration. Registration also provides the listener with information about the database instances and the service handlers available for each instance.

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:.