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摘自orafaqOne should implement a monitoring system to constantly monitor the following aspects of a database. This can be achieved by writing custom scripts, implementing Oracle's Enterprise Manager, or buying a third-party monitoring product. If an alarm is triggered, the system should automatically notify the DBA (e-mail, page, etc.) to take appropriate action.Infrastructure availability:Is the database up and responding to requestsAre the listeners up and responding to requestsAre the Oracle

摘自orafaqOne of the biggest responsibilities of a DBA is to ensure that the Oracle database is tuned properly. The Oracle RDBMS is highly tunable and allows the database to be monitored and adjusted to increase its performance.One should do performance tuning for the following reasons:The speed of computing might be wasting valuable human time (users waiting for response); Enable your system to keep-up with the speed business is conducted; and Optimize hardware usage to save money (companies ar

The instance mounts a database to associate the database with that instance. To mountthe database, the instance finds the database control files and opens them. Control filesare specified in the CONTROL_FILES initialization parameter in the parameter fileused to start the instance. Oracle then reads the control files to get the names of thedatabase’s datafiles and redo log files.At this point, the database is still closed and is accessible only to the databaseadministrator. The database adminis

In unusual circumstances, a previous instance might not have been shut down cleanly.For example, one of the instance’s processes might not have terminated properly. Insuch situations, the database can return an error during normal instance startup. Toresolve this problem, you must terminate all remnant Oracle processes of the previousinstance before starting the new instance异常情况下强制启动管理员需要在启动实例前手工结束系统中残留的 Oracle 进程才能解决这个问题[@more@]

You can start an instance in restricted mode (or later alter an existing instance to be inrestricted mode). This restricts connections to only those users who have been grantedthe RESTRICTED SESSION system privilege.以限制模式启动实例管理员可以用限制模式启动实例 . 运行在限制模式下的实例只允许具有 RESTRICTED SESSION系统权限的用户连接到数据库[@more@]

When Oracle starts an instance, it reads the server parameter file (SPFILE) orinitialization parameter file to determine the values of initialization parameters. Then,it allocates an SGA, which is a shared area of memory used for database information,and creates background processes. At this point, no database is associated with thesememory structures and processes.实例是如何启动的当 Oracle 启动实例时，首先需要从服务器参数文件或初始化参数文件中读取初始化参数，之后创建存储数据库信息的共享内存区SG

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