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The program interface consists of the following pieces:■ Oracle call interface (OCI) or the Oracle runtime library (SQLLIB)■ The client or user side of the program interface (also called the UPI)■ Various Oracle Net Services drivers (protocol-specific communications software)■ Operating system communications software■ The server or Oracle side of the program interface (also called the OPI)Both the user and Oracle sides of the program interface run Oracle software, as do thedrivers.Oracle Ne

The program interface is the software layer between a database application andOracle. The program interface:■ Provides a security barrier, preventing destructive access to the SGA by client userprocesses■ Acts as a communication mechanism, formatting information requests, passingdata, and trapping and returning errors■ Converts and translates data, particularly between different types of computers orto external user program datatypesThe Oracle code acts as a server, performing database tasks

The user and server processes are separate, distinct processes. The separate serverprocess created on behalf of each user process is called a dedicated server process (orshadow process), because this server process acts only on behalf of the associated userprocess.This configuration maintains a one-to-one ratio between the number of user processesand server processes. Even when the user is not actively making a database request,the dedicated server process remains (though it is inactive and can

top命令和ps命令的基本作用是相同的，显示系统当前的进程和其它状况；但是top是一个动态显示过程，即可以通过用户按键来不断刷新当前状态。如? 前台执行该命令，它将独占前台，直到用户终止该程序为止。比较准确的说，top命令提供了实时的对系统处理器的状态监视。它将显示系统中CPU最“敏感”的任务列表。该命令可以按CPU使用、内存使用、执行时间对任务进行排序；而且该命令的很多特性都可以通过交互式命令或者在个人定制文件中进行设定。在后面的介绍中将把命令参数和交互命令分开讲述。top命令语法：top [-] [d delay] [q] [c] [s] [S

Certain administrative activities cannot be performed while connected to a dispatcherprocess, including shutting down or starting an instance and media recovery. An errormessage is issued if you attempt to perform these activities while connected to adispatcher process.These activities are typically performed when connected with administrator privileges.When you want to connect with administrator privileges in a system configured withshared servers, you must state in your connect string that you

Each shared server process serves multiple client requests in the shared serverconfiguration. Shared server processes and dedicated server processes provide thesame functionality, except shared server processes are not associated with a specificuser process. Instead, a shared server process serves any client request in the sharedserver configuration.The PGA of a shared server process does not contain user-related data (which needs tobe accessible to all shared server processes). The PGA of a sha

The dispatcher processes support shared server configuration by allowing userprocesses to share a limited number of server processes. With the shared server, fewershared server processes are required for the same number of users, Therefore, theshared server can support a greater number of users, particularly in client/serverenvironments where the client application and server operate on different computers.You can create multiple dispatcher processes for a single database instance. At leastone d

A request from a user is a single program interface call that is part of the user’s SQLstatement. When a user makes a call, its dispatcher places the request on the requestqueue, where it is picked up by the next available shared server process.The request queue is in the SGA and is common to all dispatcher processes of aninstance. The shared server processes check the common request queue for newrequests, picking up new requests on a first-in-first-out basis. One shared serverprocess picks up

Shared server architecture eliminates the need for a dedicated server process for eachconnection. A dispatcher directs multiple incoming network session requests to a poolof shared server processes. An idle shared server process from a shared pool of serverprocesses picks up a request from a common queue, which means a small number ofshared servers can perform the same amount of processing as many dedicated servers.Also, because the amount of memory required for each user is relatively small, le

Each server and background process can write to an associated trace file. When aprocess detects an internal error, it dumps information about the error to its trace file.If an internal error occurs and information is written to a trace file, the administratorshould contact Oracle Support Services.All filenames of trace files associated with a background process contain the name ofthe process that generated the trace file. The one exception to this is trace filesgenerated by job queue processes (

There are several other background processes that might be running. These caninclude the following:MMON performs various manageability-related background tasks, for example:■ Issuing alerts whenever a given metrics violates its threshold value■ Taking snapshots by spawning additional process (MMON slaves)■ Capturing statistics value for SQL objects which have been recently modifiedMMNL performs frequent and light-weight manageability-related tasks, such assession history capture and metrics c

The queue monitor process is an optional background process for Oracle StreamsAdvanced Queuing, which monitors the message queues. You can configure up to 10queue monitor processes. These processes, like the job queue processes, are differentfrom other Oracle background processes in that process failure does not cause theinstance to fail.队列监视进程是个可选的进程for Oracle Streams Advanced Queuing, 用来监视信息队列[@more@]

The archiver process (ARCn) copies redo log files to a designated storage device aftera log switch has occurred. ARCn processes are present only when the database is inARCHIVELOG mode, and automatic archiving is enabled.An Oracle instance can have up to 10 ARCn processes (ARC0 to ARC9). The LGWRprocess starts a new ARCn process whenever the current number of ARCn processes isinsufficient to handle the workload. The alert log keeps a record of when LGWR startsa new ARCn process.If you anticipate

Job queue processes are used for batch processing. They run user jobs. They can beviewed as a scheduler service that can be used to schedule jobs as PL/SQL statementsor procedures on an Oracle instance. Given a start date and an interval, the job queueprocesses try to run the job at the next occurrence of the interval.Job queue processes are managed dynamically. This allows job queue clients to usemore job queue processes when required. The resources used by the new processes arereleased when th

The recoverer process (RECO) is a background process used with the distributeddatabase configuration that automatically resolves failures involving distributedtransactions. The RECO process of a node automatically connects to other databasesinvolved in an in-doubt distributed transaction. When the RECO process reestablishesa connection between involved database servers, it automatically resolves all in-doubttransactions, removing from each database’s pending transaction table any rows thatcorre

The process monitor (PMON) performs process recovery when a user process fails.PMON is responsible for cleaning up the database buffer cache and freeing resourcesthat the user process was using. For example, it resets the status of the activetransaction table, releases locks, and removes the process ID from the list of activeprocesses.PMON periodically checks the status of dispatcher and server processes, and restartsany that have stopped running (but not any that Oracle has terminated intention

The system monitor process (SMON) performs recovery, if necessary, at instancestartup. SMON is also responsible for cleaning up temporary segments that are nolonger in use and for coalescing contiguous free extents within dictionary managedtablespaces. If any terminated transactions were skipped during instance recoverybecause of file-read or offline errors, SMON recovers them when the tablespace or fileis brought back online. SMON checks regularly to see whether it is needed. Otherprocesses can

When a checkpoint occurs, Oracle must update the headers of all datafiles to recordthe details of the checkpoint. This is done by the CKPT process. The CKPT processdoes not write blocks to disk; DBWn always performs that work.The statistic DBWR checkpoints displayed by the System_Statistics monitor inEnterprise Manager indicates the number of checkpoint requests completed.检查点进程当检查点发生时 , Oracle将更新所有数据文件的头来记录检查点 .后面这句话什么意思 ? 哪位大侠告诉我一下 , 谢谢.[@more@]

When a user commits a transaction, the transaction is assigned a system changenumber (SCN), which Oracle records along with the transaction’s redo entries in theredo log. SCNs are recorded in the redo log so that recovery operations can besynchronized in Real Application Clusters and distributed databases.In times of high activity, LGWR can write to the redo log file using group commits. Forexample, assume that a user commits a transaction. LGWR must write thetransaction’s redo entries to disk

LGWR writes synchronously to the active mirrored group of redo log files. If one ofthe files in the group is damaged or unavailable, LGWR continues writing to otherfiles in the group and logs an error in the LGWR trace file and in the system alert log.If all files in a group are damaged, or the group is unavailable because it has not beenarchived, LGWR cannot continue to function.When a user issues a COMMIT statement, LGWR puts a commit record in the redo logbuffer and writes it to disk immediat