Chapter 2 : Oracle Net Architecture
Connectivity Concepts and Terminology:
l Database Services
An Oracle database is represented to clients as a service; that is, the database performs work on behalf of clients. A database can have one or more services associated with it. A database can be presented as multiple services and a service can be implemented as multiple database instances.
Database Database Service Database Instance
1 : n
1 : n
l Service Name
1. A logical representation of a database
2. The way a database is presented to clients
The service name is a string that is the global name, that is, a name composed of the database name and domain name, entered during installation or database creation. The service name is included in the connect data part of the connect descriptor.
l Connect Descriptor
1. Location of the database
2. Name of the database service
To connect to a database service, clients use a connect descriptor that provides the location of the database and the name of the database service. The address portion of the connect descriptor is actually the protocol address of the listener.
1. Receives client connection requests
2. Hands requests to the database server
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 hands these requests to the database server. Once the connection is established, the client and database server communicate directly. Much like a business address, the listener is configured to accept request from clients at a protocol address. This address defines the protocol the listener is listening on and any other protocol specific information.
l Service Registration
1. Database registers information with the listener
2. Service handlers available for each instance
The connect descriptor also specifies the database service name with which clients seek to
Establish a connection. The listener knows which services can be sent connection requests, because an Oracle database dynamically registers this information with the listener. This process of registration is called service registration. It also provides the listener with information about the database instances and the service handlers available for each instance.
l Service Handlers
1. Connection points
2. Dispatcher or dedicated server
Service handlers act as connection points to an Oracle database server. A service handler can be a dispatcher or a dedicated server.
Oracle Net Configuration Models:
Configuration information can be stored in a localized configuration file or a centralized repository.
l Localized management
Network address information stored in tnsnames.ora file on each computer in the network.
n Local file on each computer in the network
l Centralized management
Network address information stored in centralized directory services, including a LDAP-compliant directory server or an Oracle Names server.
n LDAP-compliant directory server
n Oracle Names server
Note: In future releases, Oracle Names will not be supported as a centralized naming method.
Overview of Naming Methods:
l Naming methods are used by a client application to resolve a connect identifier to a connect descriptor when attempting to connect to a database service.
l Oracle Net provides five naming methods
1 Host naming
Enables users in a TCP/IP environment to resolve names through their existing name resolution service
2 Local naming
Locates network address by using information configured and stored on each individual client’s tnsnames.ora file
3 Directory naming
Resolves a database service or net service name to a connect descriptor, stored in a central directory server.
4 Oracle Names
Oracle directory service made up of a system of Oracle Names servers that provide name-to-address resolution for each service on the network.
5 External naming
Use a supported third-party naming service
A small organization with only a few database can use host naming to store names in an existing
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