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To maximize performance and accommodate many users, a multiprocess Oraclesystem uses some additional Oracle processes called background processes.An Oracle instance can have many background processes; not all are always present.There are numerous background processes. See the V$BGPROCESS view for moreinformation on the background processes. The background processes in an Oracleinstance can include the following:■ Database Writer Process (DBWn)■ Log Writer Process (LGWR)■ Checkpoint Process (C

Oracle creates server processes to handle the requests of user processes connected tothe instance. In some situations when the application and Oracle operate on the samecomputer, it is possible to combine the user process and corresponding server processinto a single process to reduce system overhead. However, when the application andOracle operate on different computers, a user process always communicates withOracle through a separate server process.Server processes (or the server portion of co

This section describes the two types of processes that run the Oracle database servercode (server processes and background processes). It also describes the trace files andalert logs, which record database events for the Oracle processes.Oracle进程运行Oracle数据库服务代码的两种类型的进程 : 服务器进程和后台进程跟踪文件和预警日志文件 , 用来记录Oracle进程的数据库事件[@more@]

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Parameter type : IntegerDefault value : 0Modifiable : NoRange of values : 0 to the maximum number of enabled threadsReal Application Clusters : If specified, multiple instances must have different values.THREAD is a Real Application Clusters parameter that specifies the number of the redo thread to be used by an instance.When you create a database, Oracle creates and enables thread 1 as a public thread (one that can be used by any instance). You must create and enable subsequent threads using th

Parameter type : IntegerDefault value : Set automatically by OracleModifiable : NoRange of values : 0 to unlimitedBasic : NoCaution: On most platforms, Oracle automatically sets the value of CPU_COUNT to the number of CPUs available to your Oracle instanceDo not change the value of CPU_COUNT.CPU_COUNT specifies the number of CPUs available to Oracle. On single-CPUcomputers, the value of CPU_COUNT is 1.[@more@]

摘自OrafaqThere is no single system table which contains the high water mark (HWM) for a table. A table's HWM can be calculated using the results from the following SQL statements:SELECT BLOCKS FROM DBA_SEGMENTS WHERE OWNER=UPPER(owner) AND SEGMENT_NAME = UPPER(table); ANALYZE TABLE owner.table ESTIMATE STATISTICS; SELECT EMPTY_BLOCKS FROM DBA_TABLES WHERE OWNER=UPPER(owner) AND TABLE_NAME = UPPER(table);Thus, the tables' HWM = (query result 1) - (query result 2) - 1NOTE: You can

摘自OrafaqFollow these steps to rename a database:Start by making a full database backup of your database (in case you need to restore if this procedure is not working). Execute this command from sqlplus while connected to 'SYS AS SYSDBA':ALTER DATABASE BACKUP CONTROLFILE TO TRACE RESETLOGS; Locate the latest dump file in your USER_DUMP_DEST directory (show parameter USER_DUMP_DEST) - rename it to something like dbrename.sql. Edit dbrename.sql, remove all headers and comments, and change the dat

摘自OrafaqNo, this is listed as Enhancement Request 158508. Workaround:Do a user-level export of user A create new user B import system/manager fromuser=A touser=B drop user A [@more@]

Connection and session are closely related to user process but are very different inmeaning.A connection is a communication pathway between a user process and an Oracleinstance. A communication pathway is established using available interprocesscommunication mechanisms (on a computer that runs both the user process andOracle) or network software (when different computers run the database applicationand Oracle, and communicate through a network).A session is a specific connection of a user to an

When a user runs an application program (such as a Pro*C program) or an Oracle tool(such as Enterprise Manager or SQL*Plus), Oracle creates a user process to run theuser’s application.用户进程当用户运行应用程序或者Oracle工具时 , Oracle创建一个用户进程来运行应用程序[@more@]

The processes in an Oracle system can be categorized into two major groups:■ User processes run the application or Oracle tool code.■ Oracle processes run the Oracle database server code. They include serverprocesses and background processes.The process structure varies for different Oracle configurations, depending on theoperating system and the choice of Oracle options. The code for connected users canbe configured as a dedicated server or a shared server.With dedicated server, for each user

Multiple-process Oracle (also called multiuser Oracle) uses several processes to rundifferent parts of the Oracle code and additional processes for the users—either oneprocess for each connected user or one or more processes shared by multiple users.Most database systems are multiuser, because one of the primary benefits of adatabase is managing data needed by multiple users at the same time.Each process in an Oracle instance performs a specific job. By dividing the work ofOracle and database a

All connected Oracle users must run two modules of code to access an Oracle databaseinstance.■ Application or Oracle tool: A database user runs a database application (such as aprecompiler program) or an Oracle tool (such as SQL*Plus), which issues SQLstatements to an Oracle database.■ Oracle database server code: Each user has some Oracle database code executingon his or her behalf, which interprets and processes the application’s SQLstatements.These code modules are run by processes. A proc

摘自左岸1． This moment will nap, you will have a dream; But this moment study,you will interpret a dream. 此刻打盹，你将做梦；而此刻学习，你将圆梦。2. I leave uncultivated today, was precisely yesterday perishestomorrow which person of the body implored. 我荒废的今日，正是昨日殒身之人祈求的明日。3. Thought is already is late, exactly is the earliest time. 觉得为时已晚的时候，恰恰是最早的时候。4. Not matter of the today will drag tomorrow. 勿将今日之事拖到明日。5. Time the study pain is temporar

Software Code Areas (105)Software code areas are portions of memory used to store code that is being run or canbe run. Oracle code is stored in a software area that is typically at a different locationfrom users’ programs—a more exclusive or protected location.Software areas are usually static in size, changing only when software is updated orreinstalled. The required size of these areas varies by operating system.Software areas are read only and can be installed shared or nonshared. When poss

Memory allocation depends, in some specifics, on whether the system uses dedicatedor shared server architecture. Differences in Memory Allocation Between Dedicated and Shared ServersMemory Area Dedicated Server Shared ServerNature of session memory Private SharedLocation of the persistent area PGA SGALocation of part of the runtime area for SELECT stat

There are fixed views and columns that provide PGA memory use statistics. Most ofthese statistics are enabled when PGA_AGGREGATE_TARGET is set.■ Statistics on allocation and use of work area memory can be viewed in thefollowing dynamic performance views:V$SYSSTATV$SESSTATV$PGASTATV$SQL_WORKAREAV$SQL_WORKAREA_ACTIVE■ The following three columns in the V$PROCESS view report the PGA memoryallocated and used by an Oracle process:PGA_USED_MEMPGA_ALLOCATED_MEMPGA_MAX_MEM1. pga的统计数据可从V$SYSST

You can automatically and globally manage the size of SQL work areas. The databaseadministrator simply needs to specify the total size dedicated to PGA memory for theOracle instance by setting the initialization parameter PGA_AGGREGATE_TARGET. Thespecified number (for example, 2G) is a global target for the Oracle instance, andOracle tries to ensure that the total amount of PGA memory allocated across alldatabase server processes never exceeds this target.With PGA_AGGREGATE_TARGET, sizing of wor