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The three steps to starting an Oracle database and making it available for systemwideuse are:1. Start an instance.2. Mount the database.3. Open the database.A database administrator can perform these steps using the SQL*Plus STARTUPstatement or Enterprise Manager实例与数据库启动 1. 启动实例 2. 装载数据库 3. 打开数据库[@more@]

The database administrator can adjust variable parameters to improve theperformance of a database system. Exactly which parameters most affect a systemdepends on numerous database characteristics and variables.Some parameters can be changed dynamically with the ALTER SESSION or ALTERSYSTEM statement while the instance is running. Unless you are using a serverparameter file (SPFILE), changes made using the ALTER SYSTEM statement are onlyin effect for the current instance. You must manually update

To start an instance, Oracle must read either an initialization parameter file or aserver parameter file. These files contain a list of configuration parameters for thatinstance and database. Oracle traditionally stored initialization parameters in a textinitialization parameter file. You can also choose to maintain initialization parametersin a binary server parameter file (SPFILE).Initialization parameters stored in a server parameter file are persistent, in that anychanges made to the paramet

Database startup and shutdown are powerful administrative options and are restrictedto users who connect to Oracle with administrator privileges. Depending on theoperating system, one of the following conditions establishes administrator privilegesfor a user:■ The user’s operating system privileges allow him or her to connect usingadministrator privileges.■ The user is granted the SYSDBA or SYSOPER privileges and the database usespassword files to authenticate database administrators.When you

After starting an instance, Oracle associates the instance with the specified database.This is a mounted database. The database is then ready to be opened, which makes itaccessible to authorized users.Multiple instances can run concurrently on the same computer, each accessing its ownphysical database. In large-scale cluster systems, Real Application Clusters enablesmultiple instances to mount a single database.Only the database administrator can start up an instance and open the database. If ad

Every running Oracle database is associated with an Oracle instance. When a databaseis started on a database server (regardless of the type of computer), Oracle allocates amemory area called the System Global Area (SGA) and starts one or more Oracleprocesses. This combination of the SGA and the Oracle processes is called an Oracleinstance. The memory and processes of an instance manage the associated database’sdata efficiently and serve the one or multiple users of the database.Oracle实例SGA加O

Dynamic service registration reduces the administrative overhead for multipledatabases or instances. Information about the services to which the listener forwardsclient requests is registered with the listener. Service information can be dynamicallyregistered with the listener through a feature called service registration or staticallyconfigured in the listener.ora file.Service registration relies on the PMON process—an instance background process—toregister instance information with a listene

When an instance starts, a listener process establishes a communication pathway toOracle. When a user process makes a connection request, the listener determineswhether it should use a shared server dispatcher process or a dedicated server processand establishes an appropriate connection.The listener also establishes a communication pathway between databases. Whenmultiple databases or instances run on one computer, as in Real Application Clusters,service names enable instances to register automa

Oracle’s support of industry network protocols provides an interface between Oracleprocesses running on the database server and the user processes of Oracle applicationsrunning on other computers of the network.The Oracle protocols take SQL statements from the interface of the Oracle applicationsand package them for transmission to Oracle through one of the supportedindustry-standard higher level protocols or programmatic interfaces. The protocolsalso take replies from Oracle and package them f

Oracle Net Services provides enterprise-wide connectivity solutions in distributed,heterogeneous computing environments. Oracle Net Services enables a networksession from a client application to an Oracle database.Oracle Net Services uses the communication protocols or application programmaticinterfaces (APIs) supported by a wide range of networks to provide a distributeddatabase and distributed processing for Oracle.■ A communication protocol is a set of rules that determine how applications a

A database server provides the data requested by an application server on behalf of aclient. The database server does all of the remaining query processing.The Oracle database server can audit operations performed by the application serveron behalf of individual clients as well as operations performed by the applicationserver on its own behalf. For example, a client operation can be a request forinformation to be displayed on the client, whereas an application server operation canbe a request fo

An application server provides access to the data for the client. It serves as aninterface between the client and one or more database servers, which provides anadditional level of security. It can also perform some of the query processing for theclient, thus removing some of the load from the database server.The application server assumes the identity of the client when it is performingoperations on the database server for that client. The application server’s privilegesare restricted to preve

A client initiates a request for an operation to be performed on the database server.The client can be a Web browser or other end-user process. In a multitier architecture,the client connects to the database server through one or more application servers.客户端需要在数据库服务器上执行的操作最初是由客户端提交的。客户端可以是一个 Web浏览器或其他终端用户进程.在一个多层体系结构中，客户端需要通过一个或多个应用服务器和数据库服务器通信。[@more@]

In a multitier architecture environment, an application server provides data for clientsand serves as an interface between clients and database servers. This architecture isparticularly important because of the prevalence of Internet use.This architecture enables use of an application server to:■ Validate the credentials of a client, such as a Web browser■ Connect to a database server■ Perform the requested operation多层体系结构概述1. 在一个采用多层体系结构的系统中，客户端与数据库服务器间

Oracle client/server architecture in a distributed processing environment provides thefollowing benefits:■ Client applications are not responsible for performing any data processing. Rather,they request input from users, request data from the server, and then analyze andpresent this data using the display capabilities of the client workstation or theterminal (for example, using graphics or spreadsheets).■ Client applications are not dependent on the physical location of the data. Even ifthe da

Distributed processing is the use of more than one processor, located in differentsystems, to perform the processing for an individual task. Examples of distributedprocessing in Oracle database systems appear in Figure10–1.■ In Part A of the figure, the client and server are located on different computers,and these computers are connected through a network. The server and clients ofan Oracle database system communicate through Oracle Net Services, Oracle’snetwork interface.■ In Part B of the

In the Oracle database system environment, the database application and the databaseare separated into two parts: a front-end or client portion, and a back-end or serverportion—hence the term client/server architecture. The client runs the databaseapplication that accesses database information and interacts with a user through thekeyboard, screen, and pointing device, such as a mouse. The server runs the Oraclesoftware and handles the functions required for concurrent, shared data access to anO

The DBMS_METADATA package provides interfaces for extracting complete definitionsof database objects. The definitions can be expressed either as XML or as SQL DDL.Two styles of interface are provided:■ A flexible, sophisticated interface for programmatic control■ A simplified interface for ad hoc querying数据库对象元数据DBMS_METADATA 包为用户提供了获取数据库对象完整定义的接口。此包可以通过 XML 或 SQL DDL的形式提供定义信息[@more@]

The NO_EXPAND hint prevents the cost-based optimizer from considering OR-expansion forqueries having OR conditions or INLISTS in the WHERE clause. Normally, the optimizer wouldconsider using OR expansion and use this method if it decides the cost is lower than notusing it.SELECT /*+ NO_EXPAND */ name, salary FROM emp WHERE cost_center=9 OR cost_center=10;[@more@]

The table named DUAL is a small table in the data dictionary that Oracle anduser-written programs can reference to guarantee a known result. This table has onecolumn called DUMMY and one row containing the value X.DUAL表1. Oracle 及用户程序可以使用此表来获得一个确定的值2. 此表只有一列名为 DUMMY；只有一行数据，值为 X[@more@]