概念第14章內(nèi)存體系結(jié)構(gòu)

1、any question please contact martin.tianView PDFView PDFPrevious NextPrevious Next14 Memory ArchitectureThis chapter discusses the memory architecture of an Oracle Database instance.This chapter contains the following sections:· Introduction to Oracle Database Memory Structureso Basic Memory Str

2、uctureso Oracle Database Memory Management· Overview of the User Global Area· Overview of the Program Global Areao Contents of the PGAo PGA Usage in Dedicated and Shared Server Modes· Overview of the System Global Areao Database Buffer Cacheo Redo Log Buffero Shared Poolo Large Poolo

3、Java Poolo Streams Poolo Fixed SGA· Overview of Software Code Areas第 14 章 內(nèi)存架構(gòu)本章討論 Oracle 數(shù)據(jù)庫實(shí)例的內(nèi)存架構(gòu)。本章包含以下各節(jié)：Oracle 數(shù)據(jù)庫內(nèi)存結(jié)構(gòu)簡介·基本內(nèi)存結(jié)構(gòu)Oracle 數(shù)據(jù)庫內(nèi)存管理oo··用戶全局區(qū)概述程序全局區(qū)概述PGA 的內(nèi)容在和共享服務(wù)器模式中使用 PGAoo·系統(tǒng)全局區(qū)概述數(shù)據(jù)庫緩沖區(qū)高速緩存重做日志緩沖區(qū)共享池大池Java 池流池固定 SGAo o o o o oo 代碼區(qū)概述·See Also:Oracle D

4、atabase Administrator's Guide for instructions for configuring and managing memoryIntroduction to Oracle Database Memory StructuresWhen an instance is started, Oracle Database allocates a memory area and starts background processes. The memory area stores information such as the following:另見：Ora

5、cle 數(shù)據(jù)庫管理員指南關(guān)于配置和管理內(nèi)存的說明Oracle 數(shù)據(jù)庫內(nèi)存結(jié)構(gòu)簡介當(dāng)實(shí)例啟動(dòng)時(shí)， Oracle 數(shù)據(jù)庫分配內(nèi)存區(qū)，并啟動(dòng)進(jìn)程。內(nèi)存區(qū)如下：any question please contact martin.tian· Program code程序代碼·· Information about each connected session, even if it is not currently active· Information needed during program execution, for example, the curr

6、ent state of a query from which rows are being fetched· Information such as lock data that is shared and communicated among processes· Cached data, such as data blocks and redo records, that also exists on diskSee Also:Chapter 15, "Process Architecture"Basic Memory StructuresThe

7、basic memory structures associated with Oracle Database include:·有關(guān)每個(gè)已連接會(huì)話的，無論其當(dāng)前是否處于活動(dòng)狀態(tài)在程序執(zhí)行期間所需的，例如，正在索取數(shù)據(jù)的的當(dāng)前狀態(tài)··在多個(gè)進(jìn)程之間被共享和傳遞的，如鎖·緩存數(shù)據(jù)，如數(shù)據(jù)塊和重做等，它們也于磁盤上另見：第 15 章， "進(jìn)程體系結(jié)構(gòu)"基本內(nèi)存結(jié)構(gòu)與 Oracle 數(shù)據(jù)庫相關(guān)聯(lián)的基本內(nèi)存結(jié)構(gòu)：System global area (SGA)系統(tǒng)全局區(qū) （SGA）··The SGA is a group

8、of shared memory structures, known as SGA components, that contain data and control information for one Oracle Database instance. The SGA is shared by all server and background processes. Examples of data stored in the SGA include cached data blocks and shared SQL areas.Program global area (PGA)SGA

9、是一組稱為 SGA 組件的共享內(nèi)存結(jié)構(gòu)，其中包含一個(gè) Oracle。SGA 由所有服務(wù)器進(jìn)程和數(shù)據(jù)庫實(shí)例的數(shù)據(jù)和享。例如，SGA 中進(jìn)程共的數(shù)據(jù)數(shù)據(jù)塊緩存和共享 SQL 區(qū)。程序全局區(qū) (PGA)··A PGA is a nonshared memory region that contains data and control information exclusively for use by an Oracle process. The PGA is created by Oracle Database when an Oracle process is starte

10、d.One PGA exists for each server process and background process. The collection of individual PGAs is the total instance PGA, or instance PGA. Database initialization parameters set the size of the instance PGA, not individual PGAs.User Global Area (UGA)PGA 是一個(gè)非共享的內(nèi)存區(qū)域，其中包含專門供某個(gè) Oracle 進(jìn)程使。Oracle 進(jìn)程

11、啟動(dòng)時(shí)， Oracle 數(shù)據(jù)庫會(huì)為其創(chuàng)用的數(shù)據(jù)和建 PGA。每個(gè)服務(wù)器進(jìn)程和進(jìn)程都一個(gè) PGA。所有單個(gè) PGA 的集合即是總實(shí)例 PGA，或?qū)嵗?PGA。數(shù)據(jù)庫初始化參數(shù)設(shè)置實(shí)例 PGA的大小，而不是單個(gè) PGA 的大小。用戶全局區(qū) (UGA)··The UGA is memory associated with a user session. Software code areasUGA 是與某個(gè)用戶會(huì)話相關(guān)聯(lián)的內(nèi)存區(qū)。代碼區(qū)··any question please contact martin.tianSoftware code areas ar

12、e portions of memory used to store code that is being run or can be run. Oracle Database code is stored in a software area that is typically at a different location from user programsa more exclusive or protected location.Figure 14-1 illustrates the relationships among these memory structures.Figure

13、 14-1 Oracle Database Memory Structures代碼區(qū)是用來正在運(yùn)行或可能要運(yùn)行的代碼的那部分內(nèi)存。Oracle 數(shù)據(jù)庫代碼通常專門或更受保護(hù)的位置。在與用戶程序不同的位置， 一個(gè)更圖 14-1 說明了這些內(nèi)存結(jié)構(gòu)之間的圖 14-1 Oracle 數(shù)據(jù)庫內(nèi)存結(jié)構(gòu)。Description of "Figure 14-1 Oracle Database Memory Structures"Oracle Database Memory ManagementMemory management involves maintaining optimal s

14、izes for the Oracle instance memory structures as demands on the database change. OracleDescription of "Figure 14-1 Oracle Database Memory Structures"Oracle 數(shù)據(jù)庫內(nèi)存管理內(nèi)存管理涉及維護(hù) Oracle 實(shí)例內(nèi)存結(jié)構(gòu)的最優(yōu)大小，以滿足數(shù)據(jù)庫的變更需求。Oracle 數(shù)據(jù)庫基于與內(nèi)存相關(guān)的初始化參數(shù)設(shè)置來管理內(nèi)存。內(nèi)存any question please contact martin.tianDatabase manag

15、es memory based on the settings of memory-related initialization parameters. The basic options for memory management are as follows:管理的基本選項(xiàng)如下所示：Automatic memory management··自動(dòng)內(nèi)存管理You specify the target size for instance memory. The database instance automatically tunes to the target memory

16、 size, redistributing memory as needed between the SGA and the instance PGA.Automatic shared memory management您指定實(shí)例內(nèi)存的目標(biāo)大小。數(shù)據(jù)庫實(shí)例自動(dòng)優(yōu)化到這個(gè)目標(biāo)內(nèi)存大小，根據(jù)需要在 SGA 和 PGA 實(shí)例之間重新分配內(nèi)存。自動(dòng)共享內(nèi)存管理··This management mode is partially automated. You set a target size for the SGA and then have the option of sett

17、ing an aggregate target size for the PGA or managing PGA work areas individually. Manual memory management這種管理模式是部分自動(dòng)化的。您設(shè)置一個(gè) SGA 的目標(biāo)大小，然后設(shè)置 PGA 總目標(biāo)大小，或單獨(dú)管理 PGA 的各個(gè)工作區(qū)。手工內(nèi)存管理··Instead of setting the total memory size, you set many initialization parameters to manage components of the SGA a

18、nd instance PGA individually.If you create a database with Database Configuration Assistant (DBCA) and choose the basic installation option, then automatic memory management is the default.See Also:· "Memory Management" for more information about memory management options for DBAs

19、3; "Tools for Database Installation and Configuration" to learn about DBCA· Oracle Database 2 Day DBA and Oracle Database Administrator's Guide to learn about memory management options你不必設(shè)置總的內(nèi)存大小，但您需要設(shè)置許多初始化參數(shù)，以單獨(dú)管理 SGA 和 PGA 實(shí)例中的各個(gè)組件。如果你使用數(shù)據(jù)庫配置助手 （DBCA）來創(chuàng)建數(shù)據(jù)庫，并選擇了基本安裝選項(xiàng)，則將缺省使用自動(dòng)內(nèi)

20、存管理。另見："內(nèi)存管理" 有關(guān)供數(shù)據(jù)庫管理員使用的內(nèi)存管理選項(xiàng)的詳細(xì)··數(shù)據(jù)庫安裝和配置工具了解 DBCAOracle 數(shù)據(jù)庫 2 日 DBA 和 Oracle 數(shù)據(jù)庫管理員指南有關(guān)內(nèi)存管理的選項(xiàng)·Overview of the User Global AreaThe UGA is session memory, which is memory allocated for session variables, such as logon information, and other information required by a data

21、base session. Essentially, the UGA stores the session state. Figure 14- 2 depicts the UGA.用戶全局區(qū)概述UGA 是為會(huì)話變量分配的會(huì)話內(nèi)存，如登錄和數(shù)據(jù)庫會(huì)話所需的其他。實(shí)際上，UGA了會(huì)話狀態(tài)。圖 14-2 描述了 UGA。any question please contact martin.tianFigure 14-2 User Global Area (UGA)圖 14-2 用戶全局區(qū) (UGA)Description of "Figure 14-2 User Global Area (

22、UGA)"If a session loads a PL/SQL package into memory, then the UGA contains the package state, which is the set of values stored in all the package variables at a specific time (see "PL/SQL Packages"). The package state changes when a package subprogram changes the variables. By defau

23、lt, the package variables are unique to and persist for the life of the session. The OLAP page pool is also stored in the UGA. This pool manages OLAP data pages, which are equivalent to data blocks. The page pool is allocated at the start of an OLAP session and released at the end of the session. An

24、 OLAP session opens automatically whenever a user queries a dimensional object such as a cube.The UGA must be available to a database session for the life of the session. For this reason, the UGA cannot be stored in the PGA when using a shared server connection because the PGA is specific to a singl

25、e process. Therefore, the UGA is stored in the SGA when using shared server connections, enabling any shared server process access to it. When using a dedicated server connection, the UGA is stored in the PGA.See Also:· "Connections and Sessions"Description of "Figure 14-2 User G

26、lobal Area (UGA)"如果某個(gè)會(huì)話將 PL/SQL 包加載到內(nèi)存，則在 UGA 中包含包狀態(tài)，即是所 有包變量在某個(gè)特定的時(shí)刻所的值集（見"PL/SQL 包"）。當(dāng)包的子程序更改變量的值時(shí)，包狀態(tài)也將更改。默認(rèn)情況下，包變量在會(huì)話的存活期間是唯一且持久的。OLAP 頁面緩沖頁面。頁面緩沖在 UGA 中。該池管理相當(dāng)于數(shù)據(jù)塊的 OLAP 數(shù)據(jù)啟動(dòng)一個(gè) OLAP 會(huì)話時(shí)分配，并在該會(huì)話結(jié)束時(shí)。對象（如立方體）時(shí)，就會(huì)自動(dòng)打開一個(gè) OLAP 會(huì)每當(dāng)用戶話。一個(gè)該 UGA 必須在數(shù)據(jù)庫會(huì)話的整個(gè)存活期間是可用的。由于這個(gè)，當(dāng)使用共享服務(wù)器的連接時(shí)，UGA 不能

27、在 PGA 中，因?yàn)?PGA 是特定于單個(gè)進(jìn)程的。因此，當(dāng)使用共享服務(wù)器的連接時(shí)， UGA 被在 SGA 中，以使它。在使用服務(wù)器的連接時(shí)，UGA任何共享服務(wù)器進(jìn)程都能在 PGA 中。另見："連接和會(huì)話"·· Oracle Database Net Services Administrator's Guide to learn about shared server connections· Oracle OLAP User's Guide for an overview of Oracle OLAP·Oracle 數(shù)

28、據(jù)庫網(wǎng)絡(luò)服務(wù)管理員指南了解共享服務(wù)器連接Oracle OLAP 用戶指南關(guān)于 Oracle OLAP 的概述·Overview of the Program Global Area程序全局區(qū)概述PGA 是特定于一個(gè)操作系統(tǒng)進(jìn)The PGA is memory specific to an operating process or ththat is not線程的內(nèi)存區(qū)，且不和系統(tǒng)上的其他進(jìn)shared by other processes or ths on the system. Because the PGA is線程共享。由于 PGA 是特定于進(jìn)程的，所以它決在 SGA 中分配

29、。any question please contact martin.tianprocess-specific, it is never allocated in the SGA.The PGA is a memory heap that contains session-dependent variables required by a dedicated or shared server process. The server process allocates memory structures that it requires in the PGA.An analogy for a

30、PGA is a temporary countertop workspace used by a file clerk. In this analogy, the file clerk is the server process doing work onPGA 是包含某個(gè)或共享服務(wù)器進(jìn)程所需的會(huì)話變量的內(nèi)存堆。服務(wù)器進(jìn)程在需要時(shí)會(huì)在 PGA 中分配內(nèi)存結(jié)構(gòu)。PGA 好比是文員所使用的臨時(shí)工作臺面。在這個(gè)比喻中，文員是為客戶（客戶端進(jìn)程）服務(wù)的服務(wù)器進(jìn)程。文員出臺面的一部分，使用這個(gè)工behalf of the customer (process). The clerk clears a s

31、ection of the作空間來有關(guān)客戶要求的詳細(xì)，并對顧客請求的文件夾排序，然后countertop, uses the workspace to stores about the customer在完成工作時(shí)讓出工作空間。request and to sort the folders requested by the customer, and then gives up the space when the work is done.Figure 14-3 shows an instance PGA (collection of all PGAs) for an instance th

32、at is not configured for shared servers. You can use an initialization圖 14-3 顯示某個(gè)未配置為共享服務(wù)器的實(shí)例的 PGA（所有 PGA 的集合）。您可以使用一個(gè)初始化參數(shù)設(shè)置實(shí)例 PGA 的目標(biāo)最大大小 （請參見"內(nèi)存管理總結(jié)"）。根據(jù)需要，各個(gè) PGA 可以按需增大到這個(gè)目標(biāo)大小。parameter to set a targetum size of the instance PGA (see"Summary of Memory Management Methods"). In

33、dividual PGAs can growas needed up to this target size.Figure 14-3 Instance PGA圖 14-3 實(shí)例 PGADescription of "Figure 14-3 Instance PGA"Note:Background processes also allocate their own PGAs. This discussion focuses on server process PGAs only.Contents of the PGAThe PGA is subdivided into dif

34、ferent areas, each with a different purpose.Description of "Figure 14-3 Instance PGA"注意：進(jìn)程也分配它們的 PGA。本討論的重點(diǎn)僅限于服務(wù)器進(jìn)程 PGA。PGA 的內(nèi)容PGA 被進(jìn)一步細(xì)分為多個(gè)不同區(qū)域，每一個(gè)都有不同的目的。圖 14-4 顯示any question please contact martin.tianFigure 14-4 shows the possible contents of the PGA for a dedicated server session. Not

35、 all of the PGA areas will exist in every case.Figure 14-4 PGA Contents一個(gè)服務(wù)器會(huì)話的 PGA 中可能包含的內(nèi)容。不是所有的 PGA 區(qū)域在任何情況下都。圖 14-4 PGA 內(nèi)容Description of "Figure 14-4 PGA Contents"Private SQL AreaA private SQL area holds information about a parsed SQL statement and other session-specific information fo

36、r processing. When a server process executes SQL or PL/SQL code, the process uses the private SQL area to store bind variable values, query execution state information, and query execution work areas.Do not confuse a private SQL area, which is in the UGA, with the shared SQL area, which stores execu

37、tion plans in the SGA. Multiple private SQL areas in the same or different sessions can point to a single execution plan in the SGA. For example, 20 executions of SELECT * FROMDescription of "Figure 14-4 PGA Contents"私有 SQL 區(qū)私有 SQL 區(qū)保存了有關(guān)某個(gè)已的 SQL 語句的，和其他特定于會(huì)話的。當(dāng)服務(wù)器進(jìn)程執(zhí)行 SQL 或 PL/SQL 代碼時(shí)，該過程

38、使用其私有SQL 區(qū)域，來綁定變量值、執(zhí)行狀態(tài)、和執(zhí)行工作區(qū)。不要在 UGA 中的私有 SQL 區(qū)，和在 SGA 中執(zhí)行計(jì)劃的共享 SQL區(qū)。在相同或不同的會(huì)話中的多個(gè)私有 SQL 區(qū)，可能指向 SGA 中的一個(gè)單一執(zhí)行計(jì)劃。例如，在某個(gè)會(huì)話中運(yùn)行“SELECT * FROMemployees” 20 次，而在另一個(gè)不同的會(huì)話中運(yùn)行同一10 次，但employees in ossion and 10 executions of the same query in a它們可以共享相同的執(zhí)行計(jì)劃。每次運(yùn)行的私有 SQL 區(qū)并不共享，因此可能包含不同的值和數(shù)據(jù)。different session c

39、an share the same plan. The private SQL areas for each execution are not shared and may contain different values and data.A cursor is a name or handle to a specific private SQL area. As shown in游標(biāo)是指向某個(gè)特定的私有 SQL 區(qū)的一個(gè)名稱或句柄。如圖 14-5 所示， 你可以將游標(biāo)看成是一個(gè)從客戶端指向服務(wù)器端狀態(tài)的指針）。游標(biāo)與私有 SQL 區(qū)密切相關(guān)，這兩個(gè)術(shù)語有時(shí)可以互換使用。圖 14-5 光標(biāo)

40、Figure 14-5, you can think of a cursor as a pointer on theside andas a state on the server side. Because cursors arely associated withprivate SQL areas, the terms are sometimes used interchangeably.Figure 14-5 Cursorany question please contact martin.tianDescription of "Figure 14-5 Cursor"

41、A private SQL area is divided into the following areas:Description of "Figure 14-5 Cursor"私有 SQL 區(qū)又分為以下幾個(gè)區(qū)域：The run-time area運(yùn)行時(shí)區(qū)域··This area contains query execution state information. For example, the run-time area tracks the number of rows retrieved so far in a full table scan

42、.Oracle Database creates the run-time area as the first step of an execute request. For DML statements, the run-time area isd此區(qū)域包含執(zhí)行狀態(tài)。例如，運(yùn)行時(shí)區(qū)域會(huì)跟蹤到目前為止在掃描中檢索到的行數(shù)。Oracle 數(shù)據(jù)庫將創(chuàng)建運(yùn)行時(shí)區(qū)域，作為一個(gè)執(zhí)行請求的第一步。對于 DML 語句，其運(yùn)行時(shí)區(qū)域?qū)⒃?SQL 語句關(guān)閉時(shí)被。when the SQL statement is The persistent aread.··持久區(qū)域This area con

43、tains bind variable values. A bind variable value is d to a SQL statement at run time when the statement is此區(qū)域包含綁定變量的值。綁定變量是執(zhí)行 SQL 語句時(shí)，在運(yùn)行時(shí)提供給 SQL 語句的值。僅當(dāng)關(guān)閉該游標(biāo)時(shí)，持久區(qū)域才被。executed. The persistent area is d.d only when the cursor isTheprocess is responsible for managing private SQL areas. The客戶端進(jìn)程負(fù)責(zé)管理私有

44、 SQL 區(qū)。雖然客戶端進(jìn)程可以分配的私有 SQL 區(qū)allocation and deallocation of private SQL areas depends largely on the application, although the number of private SQL areas that aprocess can allocate is limited by the initialization parameterOPEN_CURSORS.Although most users rely on the automatic cursor handling of data

45、base utilities, the Oracle Database programmatic interfaces offer developers數(shù)量由初始化參數(shù) OPEN_CURSORS 限制，但私有 SQL 區(qū)的分配和要取決于應(yīng)用程序。主雖然大多數(shù)用戶依靠數(shù)據(jù)庫實(shí)用程序的游標(biāo)自動(dòng)處理機(jī)制，但 Oracle 數(shù)據(jù)庫編程接口仍為開發(fā)提供了對游標(biāo)的。情況下，應(yīng)用程序more control over cursors. In general, applications shouldall open應(yīng)關(guān)閉所有打開的且不再使用的游標(biāo)，以用戶的內(nèi)存需求。持久區(qū)域，并最小化應(yīng)用程序cursors t

46、hat will not be used again tothe persistent area and tominimize the memory required for application users.See Also:另見：· "Shared SQL Areas"· Oracle Database Advanced Application Developer's Guide and Oracle Database PL/SQL Language Reference to learn how to use cursorsSQL Work

47、 AreasA work area is a private allocation of PGA memory used for memory- intensive operations. For example, a sort operator uses the sort area to"共享 SQL 區(qū)"Oracle 數(shù)據(jù)庫高級應(yīng)用程序開發(fā)者指南和 Oracle 數(shù)據(jù)庫PL/SQL 語言參考了解如何使用游標(biāo)··SQL 工作區(qū)工作區(qū)是在 PGA 中為內(nèi)存密集型操作分配的私有內(nèi)存區(qū)。例如，排序操作使用排序區(qū)來對一組行進(jìn)行排序。同樣，聯(lián)接操作將其左側(cè)數(shù)據(jù)為

48、輸any question please contact martin.tiansort a set of rows. Similarly, a hash join operator uses a hash area to build a hash table from its left input, whereas a bitmap merge uses the bitmap merge area to merge data retrieves from scans of multiple bitmap indexes.Example 14-1 shows a join of employe

49、es and departments with its query plan.Example 14-1 Query Plan for Table JoinSQL> SELECT *入，并使用區(qū)來創(chuàng)建一個(gè)表，而位圖合并操作則使用位圖合并區(qū)來合并從掃描多個(gè)位圖索引檢索到的數(shù)據(jù)。示例 14-1 顯示了 employees 表和 departments 表相聯(lián)接的計(jì)劃。示例 14-1 表聯(lián)接的SQL> SELECT *2 FROMemployees e JOIN departments d計(jì)劃2 FROMemployees e JOIN departmentsd3 ONe.departme

50、nt_id=d.department_id3 ONe.department_id=d.department_id4 ORDER BY last_name;4 ORDER BY last_name;.| Id | Operation| Name| Rows | Bytes | Cost (%CPU)| Time| Id | Operation| Name| Rows | Bytes | Cost (%CPU)| Time| 0 | SELECT STATEMENT| 1 | SORT ORDER BY|* 2 | HASH JOIN|106 | 9328 |106 | 9328 |106 | 9

51、328 |27 | 540 |107 | 7276 |7 (29)| 00:00:01 |7 (29)| 00:00:01 |6 (17)| 00:00:01 |2 (0)| 00:00:01 |3 (0)| 00:00:01 | 0 | SELECT STATEMENT| 1 | SORT ORDER BY|* 2 | HASH JOIN|106 |106 |106 |27 |107 |9328 |9328 |9328 |540 | 7276 |77623(29)| 00:00:01 |(29)| 00:00:01 |(17)| 00:00:01 |(0)| 00:00:01 |(0)| 0

52、0:00:01 | 3 | TABLE ACCESS FULL| DEPARTMENTS | 3 | TABLE ACCESS FULL| DEPARTMENTS | 4 | TABLE ACCESS FULL| EMPLOYEES| 4 | TABLE ACCESS FULL| EMPLOYEES|In Example 14-1, the run-time area tracks the progress of the full table scans. The session performs a hash join in the hash area to match rows from

53、the two tables. The ORDER BY sort occurs in the sort area.If the amount of data to be processed by the operators does not fit into a work area, then Oracle Database divides the input data into smaller pieces. In this way, the database processes some data pieces in memory while writing the rest to te

54、mporary disk storage for processing later.The database automatically tunes work area sizes when automatic PGA memory management is enabled. You can also manually control and tune the size of a work area. See "Memory Management" for more information. Generally, larger work areas can signifi

55、cantly improve performance of an operator at the cost of higher memory consumption. Optimally, the size of在示例 14-1 中，運(yùn)行時(shí)區(qū)域跟蹤掃描的進(jìn)度。此會(huì)話在區(qū)中執(zhí)行一個(gè)聯(lián)接，以匹配兩個(gè)表中的行。而 ORDER BY 排序操作在排序區(qū)中進(jìn)行。如果要由該運(yùn)算符處理的數(shù)據(jù)量太大，不能在工作區(qū)中完成，則 Oracle 數(shù)據(jù)庫會(huì)將輸入數(shù)據(jù)分成更小的片斷。這樣一來，數(shù)據(jù)庫先在內(nèi)存中處理一些數(shù)據(jù)片斷，而將其余數(shù)據(jù)寫入到臨時(shí)磁盤，以待后續(xù)處理。當(dāng)啟用了自動(dòng) PGA 內(nèi)存管理時(shí)，數(shù)據(jù)庫自動(dòng)優(yōu)化工作區(qū)大

56、小。你也可以手的，請參閱"內(nèi)存管理"。動(dòng)和優(yōu)化工作區(qū)大小。通常，更大的工作區(qū)可以顯著提高操作性能，但這是以的內(nèi)存消耗為代價(jià)的。理想的情況是，工作區(qū)的大小足以容納輸入的數(shù)據(jù)，而由其關(guān)聯(lián)的any question please contact martin.tiana work area is sufficient to accommodate the input data and auxiliary memory structures allocated by its associated SQL operator. If not, response time increases because part of the input data must be cached on disk. In the extreme case, if the size of a work area is too small compared to input data size, then the database must perform multiple passes over the data pie