Client/Server Architecture

The Oracle Client/Server Architecture
SQL*Net

We must try to trust one another. Stay and cooperate.

Jomo Kenyatta

This chapter defines distributed processing and how the Oracle Server and database applications work in a distributed processing environment. This material applies to almost every type of Oracle database system environment. This chapter includes:

The Oracle Client/Server Architecture

SQL*Net

The Oracle Client/Server Architecture

In the Oracle client/server architecture, the database application and the database are separated into two parts: a front-end or client portion, and a back-end or server portion. The client executes the database application that accesses database information and interacts with a user through the keyboard, screen, and pointing device such as a mouse. The server executes the Oracle software and handles the functions required for concurrent, shared data access to an Oracle database.

Although the client application and Oracle can be executed on the same computer, it may be more efficient and effective when the client portion(s) and server portion are executed by different computers connected via a network. The following sections discuss possible variants in the Oracle client/server architecture.

Note: In a distributed database, one server (Oracle) may need to access a database on another server. In this case, the server requesting the information is a client. See Chapter 21, "Distributed Databases", for more information about clients and servers in distributed databases.

Distributed Processing

Distributed processing is the use of more than one processor to divide the processing for an individual task. The following are examples of distributed processing in Oracle database systems:

The client and server are located on different computers; these computers are connected via a network (see Figure 20 - 1, Part A).

A single computer has more than one processor, and different processors separate the execution of the client application from Oracle (see Figure 20 - 1, Part B).

Figure 20 - 1. The Client/Server Architecture and Distributed Processing

Benefits of the Oracle client/server architecture in a distributed processing environment include the following:

Client applications are not responsible for performing any data processing. Client applications can concentrate on requesting input from users, requesting desired data from the server, and then analyzing and presenting this data using the display capabilities of the client workstation or the terminal (for example, using graphics or spreadsheets).

Client applications can be designed with no dependence on the physical location of the data. If the data is moved or distributed to other database servers, the application continues to function with little or no modification.

Oracle exploits the multitasking and shared-memory facilities of its underlying operating system. As a result, it delivers the highest possible degree of concurrency, data integrity, and performance to its client applications.

Client workstations or terminals can be optimized for the presentation of data (for example, by providing graphics and mouse support) and the server can be optimized for the processing and storage of data (for example, by having large amounts of memory and disk space).

If necessary, Oracle can be scaled. As your system grows, you can add multiple servers to distribute the database processing load throughout the network (horizontally scaled). Alternatively, you can replace Oracle on a less powerful computer, such as a microcomputer, with Oracle running on a minicomputer or mainframe, to take advantage of a larger system's performance (vertically scaled). In either case, all data and applications are maintained with little or no modification, since Oracle is portable between systems.

In networked environments, shared data is stored on the servers, rather than on all computers in the system. This makes it easier and more efficient to manage concurrent access.

In networked environments, inexpensive, low-end client workstations can be used to access the remote data of the server effectively.

In networked environments, client applications submit database requests to the server using SQL statements. Once received, the SQL statement is processed by the server, and the results are returned to the client application. Network traffic is kept to a minimum because only the requests and the results are shipped over the network.

**SQL*Net**

SQL*Net is the Oracle network interface that allows Oracle tools running on network workstations and servers to access, modify, share, and store data on other servers. SQL*Net is considered part of the program interface in network communications. See Chapter 9, "Memory Structures and Processes",.for more information about the program interface.

SQL*Net uses the communication protocols or application programmatic interfaces (APIs) supported by a wide range of networks to provide a distributed database and distributed processing for Oracle. A communications protocol is a set of standards, implemented in software, that govern the transmission of data across a network. An API is a set of subroutines that provide, in the case of networks, a means to establish remote process-to-process communication via a communication protocol.

Communication protocols define the way that data is transmitted and received on a network. In a networked environment, an Oracle server communicates with client workstations and other Oracle servers using SQL*Net. SQL*Net supports communications on all major network protocols, ranging from those supported by PC LANs to those used by the largest mainframe computer systems.

Without the use of SQL*Net, an application developer must manually code all communications in an application that operates in a networked distributed processing environment. If the network hardware, topology, or protocol changes, the application has to be modified accordingly.

However, by using SQL*Net, the application developer does not have to be concerned with supporting network communications in a database application. If the underlying protocol changes, the database administrator makes some minor changes, while the application requires no modifications and will continue to function.

**How SQL*Net Works**

SQL*Net drivers provide an interface between Oracle processes running on the database server and the user processes of Oracle tools running on other computers of the network.

The SQL*Net drivers take SQL statements from the interface of the Oracle tools and package them for transmission to Oracle via one of the supported industry-standard higher level protocols or programmatic interfaces. The drivers also take replies from Oracle and package them for transmission to the tools via the same higher level communications mechanism. This is all done independently of the network operating system.

Additional Information: Depending on the operating system that executes Oracle, the SQL*Net software of the database server may include the driver software and start an additional Oracle background process; see your Oracle operating system-specific documentation for details.

For additional information on SQL*Net, refer to Understanding SQL*Net or the appropriate SQL*Net documentation.

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