14 Manageability

001 Oracle Database 10g represents a major milestone in Oracle's drive toward self-managing databases. It automates many routine administrative tasks, and considerably simplifies key DBA functions, such as performance diagnostics, SQL tuning, and space and memory management. It also provides several advisors that guide DBAs in managing key components of the database by giving specific recommendations along with potential benefit. Furthermore, Oracle Database 10g proactively sends alerts when a problem is anticipated, thus facilitating proactive rather than reactive database management.
　		 在 Oracle 逐渐发展为具备自我管理能力的（self-managing）数据库的过程中，Oracle 数据库 10g 是一个重要的里程碑。Oracle 数据库 10g 能够自动执行许多常规的数据库管理任务，同时能够显著地简化某些关键的 DBA 工作，例如性能诊断（performance diagnostic），SQL 调优（tuning），空间（space）管理及内存管理等。Oracle 10g 还提供了多个顾问工具（advisor），为数据库参数的设置提供建议并预测修改参数对数据库的影响，为 DBA 管理关键数据库组件提供了参考依据。此外，Oracle 数据库 10g 能够预测系统中可能出现的问题并提前向用户发出告警，做到了防患于未然的数据库管理。
　
002 This chapter contains the following topics: 本章包含以下主题：
003

Installing Oracle and Getting Started

14.1 安装数据库并使系统开始运转
004 The Oracle Universal Installer (OUI) is a GUI tool for installing Oracle software. It automates all installation tasks, performs comprehensive prerequisite checks (such as operating system version, software patches, and capacity), installs selected software components, and performs all postinstall configuration.
　		 Oracle 通用安装程序（Oracle Universal Installer，OUI）是用于安装 Oracle 软件的图形化工具。她能自动地执行各项安装任务，进行安装先决条件检查（例如操作系统版本，软件补丁，磁盘容量等），安装用户选择的软件组件，并执行安装后的配置 工作。
　
005 The installation process is self-contained to automatically set up the required infrastructure for routine monitoring and administration. The Enterprise Manager Database Management Console is automatically configured to let you to get started with database administrative tasks without any manual configuration. The Enterprise Manager Database Console provides all essential functionality for managing a single database, including alert notification, job scheduling, and software management. In addition, all Oracle server components such as the database, listener, management framework, and so on, are configured for automated startup and shutdown.
　		 安装过程将自动地配置监控及管理工作所需的基础结构。安装结束后，企业管理器数据库管理控制台（Enterprise Manager Database Management Console）已经被自动地配置了，管理员无需手工配置就可以开始进行数据库管理工作了。企业管理器数据库管理控制台包含了管理一个单实例数据库（single database）的主要功能，包括告警提示（alert notification），作业调度（job scheduling），及软件管理。此外，所有的 Oracle 服务器组件，例如数据库，监听器，管理框架（management framework）等，都已被配置为能够自动地启动与关闭。
　
006

See Also:

"Configuration Management" for more information on Enterprise Manager
另见：

“配置管理” 了解关于企业管理器的更多信息
007

Simplified Database Creation

14.1.1 简化的数据库创建工作
008 The Database Creation Assistant (DBCA) is a GUI tool for database creation. It lets you create all possible configurations of the database, be it a standalone database, a Real Application Cluster database, or a standby database. During the database creation process, the DBCA guides you in setting up an automated disk-based backup and registering the database with a LDAP server, if available. A database created using the DBCA is fully setup and ready to use in all respects.
　		 数据库创建助手（Database Creation Assistant，DBCA）是一个图形化的数据库创建工具。用户可以使用此工具创建各种不同配置的数据库，例如单实例数据库（standalone database），RAC 数据库，或备用数据库（standby database）。在数据库创建过程中，用户可以在 DBCA 的指引下创建一个基于磁盘（disk-based）的自动备份机制，或者将数据库注册到 LDAP 服务器中。通过 DBCA 创建的数据库已经进行了全面的设置，可以马上投入使用。
　
009

Instant Client

14.1.2 即时客户端
010 The Instant Client is the simplest way to deploy a full Oracle Client application built with OCI, OCCI, JDBC-OCI, or ODBC drivers. It provides the necessary Oracle Client libraries in a small set of files. Installation is as easy as copying a few shared libraries to a directory on the client computer. If this directory is accessible through the operating system library path variable (for instance, LD_LIBRARY_PATH or PATH) then the application will operate in the Instant Client mode. Instant Client deployment does not require the ORACLE_HOME environment, nor does it require the large number of code and data files provided in a full Oracle Client install, thereby significantly reducing the client application disk space needs. There is no loss in functionality or performance for an application deployed using Instant Client when compared to the same application running in a full ORACLE_HOME environment.
　		 部署建立在 OCI，OCCI，JDBC-OCI，或 ODBC 驱动上的 Oracle 客户端应用程序时，采用即时客户端（Instant Client）是最简单的方法。即时客户端使用最少的文件包含了所有必要的 Oracle 客户端函数库。即时客户端的安装过程极为简单，只需要将客户端函数库文件复制到客户端计算机的某个目录。如果这个目录已经包含在操作系统的路径环境变量（例如 LD_LIBRARY_PATH 或 PATH）中，那么应用程序就能够利用即时客户端开始运行。即时客户端不需要 ORACLE_HOME 环境变量，也不需要完全安装的 Oracle 客户端中包含的大量程序及数据文件，因此显著地减少了客户端应用程序所需的磁盘空间。应用程序无论利用即时客户端部署，还是利用完全安装的 Oracle 客户端部署，都拥有完全相同的功能及运行性能。
　
011

See Also:

另见：
012

Automated Upgrades

14.1.3 自动升级
013 With the Database Upgrade Assistant (DBUA), you can upgrade any database configuration, including RAC and standby, just by answering a few simple questions. It automatically checks that adequate resources are available, ensures adherence to the best practices – such as backing up the database before beginning the upgrade process, replacing the obsolete and deprecate initialization parameters, and so on – and, verifies the successful completion of the operation.
　		 用户可以使用数据库升级助理（Database Upgrade Assistant，DBUA）来升级各种配置的数据库，包括 RAC 数据库及备用数据库（standby database），升级过程只需用户回答一些简单的问题。数据库升级助理能够自动地检查是否具备所需的资源，能够保证升级过程尽量完善--例如在升级前备份数据库，能够 清除废弃的初始化参数（initialization parameter），最后还能够检验数据库升级是否成功。
　
014 The upgrade process is restartable, allowing it to automatically resume from the point of interruption. You can also get a time estimation of how long the upgrade process is likely to take.
　		 升级过程可以从中断点重新开始。DBUA 可以事先告知用户升级过程预计所需的时间。
　
015

Basic Initialization Parameters

14.1.4 基本初始化参数
016 The Oracle Database provides a number of initialization parameters to optimize its operation in diverse environments. Only a few of these parameters need to be explicitly set, because the default values are adequate in the majority of cases.
　		 Oracle 数据库使用了大量的初始化参数（initialization paramete），以便用户根据不同的系统需求对数据库进行调优。但只有少量参数需要显示地设置，因为她们的默认值能够满足大多数情况的要求。
　
017 There are approximately 30 basic parameters. The remainder of the parameters are preserved to allow expert DBAs to adapt the behavior of the Oracle Database to meet unique requirements without overwhelming those who have no such requirements.
　		 Oracle 数据库有 30 个左右基本初始化参数。而基本初始化参数之外的参数供经验丰富的 DBA 使用，使数据库经过调整后能够满足独特的需求。没有特殊需求时不必改变这些参数。
　
018

See Also:

Oracle Database Administrator's Guide
另见：

Oracle Database Administrator's Guide
019

Data Loading, Transfer, and Archiving

14.1.5 数据加载，传输，及归档
020 Data Pump enables very high-speed data and metadata loading and unloading to and from the Oracle Database. It automatically manages and schedules multiple, parallel streams of load or unload for maximum throughput.
　		 数据泵（Data Pump）工具能够在 Oracle 数据库间高速地导出或加载数据及元数据。数据泵工具调度并管理多个并行地进程进行导出及加载，从而获得最大的数据吞吐量。
　
021 The transportable tablespace feature lets you quickly move a tablespace across Oracle databases. This can be much faster than performing either an export/import or unload/load of the same data, because transporting a tablespace only requires the copying of datafiles and integrating the tablespace structural information. You can also use transportable tablespaces to move index data, thereby avoiding the index rebuilds you would have to perform when importing or loading table data.
　		 用户可以利用可移动表空间（transportable tablespace）功能在数据库间快速地移动表空间。这比执行导入导出要快得多，因为在数据库间移动表空间只需复制数据文件，再导入表空间结构信息即可。用户使用可移动表空间时还能够移动索引数据， 而导入导出数据后还需要进行索引重建工作。
　
022 Data Pump functionality together with cross-platform transportable tablespace feature provides powerful, easy to use, and high performance tools for moving data in and out of the database.
　		 数据泵工具及跨平台的可移动表空间功能为用户提供了强大，易用，且高效的数据迁移途径。
　
023

See Also:

另见：
024

Intelligent Infrastructure

14.2 智能的基础结构
025 Oracle Database has a sophisticated self-management infrastructure that allows the database to learn about itself and use this information to adapt to workload variations or to automatically remedy any potential problem. The self-management infrastructure includes the following: Oracle 数据库拥有一套用于自我管理（self-management）的完善的基础结构，数据库能够利用这套基础结构了解自身的运行信息，并利用这些信息对自身进行调整以适应工作负载的变化，或自动地修正系统中的潜在问题。用于自我管理的基础结构包括以下内容：
026

Automatic Workload Repository

14.2.1 自动负载资料库
027 Automatic Workload Repository (AWR) is a built-in repository in every Oracle Database. At regular intervals, the Oracle Database makes a snapshot of all its vital statistics and workload information and stores them in AWR. By default, the snapshots are made every 60 minutes, but you can change this frequency. The snapshots are stored in the AWR for a certain period of time (seven days by default) after which they are automatically purged.
　		 自动负载资料库（Automatic Workload Repository，AWR）是 Oracle 数据库中内置的一个资料库。Oracle 会按照固定的周期对其运行信息及负载信息进行快照（snapshot），并存储在 AWR 中。快照的默认的周期为 60 分钟，用户也可以调整这个频率。快照将在 AWR 中存储一段时间（默认为 7 天），过期的快照会被自动清除。
　
028 The captured data allows both system level and user level analysis to be performed, again reducing the requirement to repeat the workload in order to diagnose problems.
　		 AWR 中的数据既可以供系统使用，也可以供用户使用，这避免了为诊断系统问题而重复地收集负载信息。
　
029 Optimizations have been performed to ensure that the capture of data is performed efficiently to minimize overhead. One example of these optimizations is in the SQL statement capture. It maintains deltas of the data for SQL statements between snapshots. These let the Oracle Database capture only statements that have significantly impacted the load of the system since the previous snapshot in an efficient manner, rather than having to capture all statements that had performed above a threshold level of work since they first appeared in the system.
　		 Oracle 已经对捕获信息的工作进行了优化，从而保证其高效执行并使系统开销最小化。以 SQL 语句捕获的优化为例，Oracle 能够记录 SQL 语句不同快照间的增量信息（delta）。因此，Oracle 不会捕获系统中超过负载阈值但只是第一次出现的 SQL 语句，而只需捕获与上一次快照相比显著影响系统负载的语句。对比这两种捕获机制，后者较前者效率更高。
　
030 AWR forms the foundation for all self-management functionality of Oracle Database. It is the source of information that gives the Oracle Database an historical perspective on how it is being used and enables it to make decisions that are accurate and specifically tailored for each environment.
　		 AWR 是 Oracle 数据库所有自我管理（self-management）功能的基础。Oracle 利用 AWR 作为信息源得以从历史的角度观察数据库是如何被使用的，从而使数据库的自动调整更精确且更符合系统的实际要求。
　
031

Automatic Maintenance Tasks

14.2.2 自动维护任务
032 By analyzing the information stored in AWR, the database can identify the need to perform routine maintenance tasks, such as optimizer statistics refresh. The automated maintenance tasks infrastructure enables the Oracle Database to automatically perform such operations. It uses the Scheduler to run such tasks in a pre-defined "maintenance window".
　		 通过分析 AWR 中的数据，Oracle 能够决定是否需要执行常规的维护任务（maintenance task），例如刷新优化器（optimizer）的统计信息。Oracle 使用自动维护任务基础结构（automated maintenance tasks infrastructure）来自动地执行此类维护操作。Oracle 使用调度器（scheduler）在预定义的维护窗口（maintenance window）内运行维护任务。
　
033 By default, the maintenance window starts at 10 PM every night and lasts until 6 AM next morning and throughout the weekend. All attributes of the maintenance window are customizable, including start and end time, frequency, days of the week, and so on. Also, the impact of automated maintenance tasks on normal database operations can be limited by associating a Database Resource Manager resource plan to the maintenance window.
　		 Oracle 中默认的维护窗口为每晚 22 点至第二天早晨 6 点及整个周末。维护窗口的属性是能够自定义的，这包括窗口的开始及结束时间，频率，一周内的哪几天等等。此外，用户还可以将数据库资源管理器（Database Resource Manager）中的资源计划应用到维护窗口，从而避免自动护任务对数据库常规操作造成影响。
　
034 Optimizer statistics are automatically refreshed using the automatic maintenance task infrastructure.
　		 优化器的统计信息是使用自动维护任务基础结构来进行刷新的。
　
035

See Also:

另见：
036

Server-Generated Alerts

14.2.3 服务器告警
037 For problems that cannot be resolved automatically and require administrators to be notified, such as running out of space, the Oracle Database provides server-generated alerts. The Oracle Database can monitor itself and send out alerts to notify you of any problem in an efficient and timely manner.
　		 对于不能自动解决而必须通知管理员的问题（例如存储空间不足），Oracle 数据库将生成服务器告警（server-generated alert）。Oracle 数据库能够进行自我监控，在出现问题时及时向用户发出告警。
　
038 Monitoring activities take place as the database performs its regular operation. This ensures that the database is aware of problems the moment they arise. The alerts produced by the Oracle Database not only notify the problem, they also provide recommendations on how the reported problem can be resolved. This ensures quick problem resolution and helps prevent potential failures.
　		 在数据库进行常规操作的时，监控活动也在同时进行。因此发生问题后 Oracle 能够马上获知。由 Oracle 数据库产生的服务器告警不仅能将问题通知给用户，还能提供如何解决问题的建议。这有助于迅速解决问题，并能预防潜在的系统故障。
　
039

Advisor Framework

14.2.4 顾问工具框架
040 The Oracle Database includes a number of advisors for different sub-systems in the database to automatically determine how the operation of the corresponding subcomponents could be further optimized. The SQL Tuning Advisor and the SQL Access Advisor, for example, provide recommendations for running SQL statements faster. Memory advisors help size the various memory components without resorting to trial-and-error techniques. The Segment Advisor handles space-related issues, such as recommending wasted-space reclamation and analyzing growth trends, while the Undo Advisor guides you in sizing the undo tablespace correctly. The various advisors are discussed more throughout this chapter.
　		 Oracle 数据库中包含了多个针对不同数据库子系统的顾问工具（advisor），用于决定如何进一步优化各个子系统。举例来说，SQL 调优顾问工具（SQL Tuning Advisor）及 SQL 数据存取顾问工具（SQL Access Advisor）能够为更快地执行 SQL 语句提供建议。用户可以根据内存顾问工具（Memory advisor）的建议调整各个内存组件的容量，而不必反复尝试调整值是否正确（trial-and-error technique）。数据段顾问工具（Segment Advisor）用于解决和空间相关的问题，例如进行空间回收（wasted-space reclamation）及分析空间增长趋势。还原管理顾问工具（Undo Advisor）能够指导用户正确地设置还原表空间的容量。本章还将详细论述各种顾问工具。
　
041 To ensure the consistency and uniformity in the way advisors function and allow them to interact with each other seamlessly, the Oracle Database includes an advisor framework. The advisor framework provides a consistent manner in which advisors are invoked and results are reported. Although these advisors are primarily used by the database to optimize its own performance, they can be invoked by administrators to get more insight into the functioning of a particular subcomponent.
　		 为了使各个顾问工具能够以一致且统一的方式工作，并使不同顾问工具间能够无缝地交互，Oracle 数据库中定义了顾问工具框架（advisor framework）。在顾问工具框架下，不同顾问工具的调用方式及结果返回方式具有一致性。数据库中的顾问工具主要供数据库优化其性能时使用，但管理员也能够调用顾问工具，从而深入了解各个子系统的运行情况。
　
042

See Also:

Oracle Database 2 Day DBA for more information on using advisors
另见：

Oracle Database 2 Day DBA 了解更多关于使用顾问工具的信息
043

Performance Diagnostic and Troubleshooting

14.3 性能诊断及故障处理
044 Building upon the data captured in AWR, the Automatic Database Diagnostic Monitor (ADDM) lets the Oracle Database diagnose its own performance and determine how identified problems could be resolved. ADDM runs automatically after each AWR statistics capture, making the performance diagnostic data readily available.
　		 Oracle 数据库中的自动数据库诊断监视器（Automatic Database Diagnostic Monitor，ADDM），能够利用 AWR 中捕获的数据对数据库性能进行分析，并决定如何解决发现的问题。AWR 每次捕获统计信息后 ADDM 将自动运行，迅速生成性能诊断信息。
　
045 ADDM examines data captured in AWR and performs analysis to determine the major issues on the system on a proactive basis. In many cases, it recommends solutions and quantifies expected benefits. ADDM takes a holistic approach to the performance of the system, using time as a common currency between components. ADDM identifies those areas of the system that are consuming the most time. ADDM drills down to identify the root cause of problems, rather than just the symptoms, and reports the impact that the problem is having on the system overall. If a recommendation is made, it reports the benefits that can be expected in terms of time. The use of time throughout allows the impact of several problems or recommendations to be compared.
　		 ADDM 能够分析 AWR 中捕获的信息，并确定系统中存在的潜在问题。对于大多数问题，ADDM 能够提出建议的解决方案并给出量化的预期效果。ADDM 总是从整体上来评估系统的性能，她使用时间作为评估系统各个组件的通用标准。ADDM 能够确定系统中哪个组件消耗的时间最多。确定了问题的表象后，ADDM 还能深入研究以确定问题的根源，并显示此问题对系统整体的影响。如果 ADDM 能够提出调优意见，她还会以时间为单位计算调整后的预期效果。统一以时间为单位使 ADDM 能够对不同的性能问题及解决方案进行比较。
　
046 ADDM focuses on activities that the database is spending most time on and then drills down through a sophisticated problem classification tree. Some common problems detected by ADDM include the following:
  • CPU bottlenecks
  • Poor connection management
  • Excessive parsing
  • Lock contention
  • I/O capacity
  • Undersizing of Oracle memory structures; for example, PGA, buffer cache, log buffer
  • High load SQL statements
  • High PL/SQL and Java time
  • High checkpoint load and cause; for example, small log files, aggressive MTTR setting
  • RAC-specific issues
 ADDM 集中分析数据库中消耗时间最多的操作，并依照一个完善的问题分类树（problem classification tree）进行深入分析。ADDM 能够检测出的通用问题包括：
  • CPU 瓶颈
  • 连接管理（connection management）问题
  • 过量的解析操作（excessive parsing）
  • 锁竞争（lock contention）
  • I/O 性能问题
  • Oracle 内存结构过小；例如 PGA，数据库缓存，重做日志缓存等
  • 执行 SQL 语句造成的负载过高
  • 执行 PL/SQL 及 Java 程序时间过长
  • 检查点（checkpoint）负载过高及原因；例如重做日志文件（log file）过小，或 MTTR 设置不适当
  • 与 RAC 相关的问题
047 Besides reporting potential performance issues, ADDM also documents non-problem areas of the system. The subcomponents, such as I/O and memory, that are not significantly impacting system performance are pruned from the classification tree at an early stage and are listed so that you can quickly see that there is little to be gained by performing actions in those areas.
　		 除了报告潜在的性能问题，ADDM 还能记录系统中没有问题的子系统。没有显著影响系统性能的子系统在诊断初期就被从问题分类树中移出，并被列在诊断结果中。用户能够清楚地了解对系统中哪些组件进行调优的效果不会太明显。
　
048 You no longer need to first collect huge volumes of diagnostic data and spend hours analyzing them in order to find out answers to performance issues. You can simply follow the recommendation made by ADDM with just a few mouse clicks.
　		 使用了 ADDM 后，用户不必手工收集大量诊断数据，并花费大量时间对数据进行分析，再设法找到解决系统性能问题的办法。用户只需轻点鼠标，参考 ADDM 的建议即可。
　
049

Application and SQL Tuning

14.4 应用调优及 SQL 调优
050 The Oracle Database completely automates the SQL tuning process. ADDM identifies SQL statements consuming unusually high system resources and therefore causing performance problems. In addition, the top SQL statements in terms of CPU and shared memory consumption are automatically captured in AWR. Thus, the identification of high load SQL statements happens automatically in the Oracle Database and requires no intervention.
　		 Oracle 数据库中的 SQL 语句调优过程是完全自动化的。ADDM 能够识别出消耗系统资源异常高并导致系统性能问题的 SQL 语句。此外 AWR 也能自动地捕获系统中消耗 CPU 或共享内存较高的语句。因此在 Oracle 数据库中，对造成高负载的 SQL 语句的识别是完全自动的，无须用户干预。
　
051 After identifying the top resource-consuming SQL statements, the Oracle Database can automatically analyze them and recommend solutions using the Automatic Tuning Optimizer. Automatic SQL Tuning is exposed with an advisor, called the SQL Tuning Advisor. The SQL Tuning Advisor takes one or more SQL statements as input and produces well-tuned plans along with tuning advice. You do not need to do anything other than invoke the SQL Tuning Advisor.
　		 当识别出消耗资源较高的 SQL 后，Oracle 数据库能自动地使用自动调优优化器（Automatic Tuning Optimizer）对其进行分析并给出建议的执行计划。而用户可以通过 SQL 调优顾问工具（SQL Tuning Advisor）来使用 Oracle 的自动 SQL 调优（Automatic SQL Tuning）功能。SQL 调优顾问工具接收一个或多个 SQL 语句作为输入，输出经过调优的 SQL 执行计划及调优建议。用户需要做的工作只是调用 SQL 调优顾问工具。
　
052 The solution comes right from the optimizer and not from external tools using pre-defined heuristics. This provides several advantages: a) the tuning is done by the system component that is ultimately responsible for the execution plans and SQL performance, b) the tuning process is fully cost-based, and it naturally accounts for any changes and enhancements done to the query optimizer, c) the tuning process considers the past execution statistics of a SQL statement and customizes the optimizer settings for that statement, and d) it collects auxiliary information in conjunction with the regular statistics based on what is considered useful by the query optimizer.
　		 在 Oracle 中 SQL 语句的执行计划是由查询优化器（query optimizer）给出的，而非其它使用预定义的探索方式（pre-defined heuristics）来优化 SQL 的外部工具。这种模式以下几个优势：a）调优工作是由最终负责生成执行计划（execution plan）及保证 SQL 执行性能的系统组件完成的，b）调优过程是完全基于成本的（cost-based），且修改了查询优化器的任何参数后都会直接影响调优结果，c）调优过程能够 参考 SQL 语句以往执行所产生的统计信息，并根据每个 SQL 语句的特性设置查询优化器，d）调优过程能够根据查询优化器的需要收集系统中其他有意义的统计信息。
　
053 The recommendation of the Automatic Tuning Optimizer can fall into one of the following categories
  • Statistics Analysis: The Automatic Tuning Optimizer checks each query object for missing or stale statistics and makes recommendations to gather relevant statistics. It also collects auxiliary information to supply missing statistics or correct stale statistics in case recommendations are not implemented. Because the Oracle Database automatically gathers optimizer statistics, this should not be the problem unless the automatic statistics gathering functionality has been disabled.
  • SQL Profiling: The Automatic Tuning Optimizer verifies its own estimates and collects auxiliary information to remove estimation errors. It also collects auxiliary information in the form of customized optimizer settings (for example, first rows or all rows) based on past execution history of the SQL statement. It builds a SQL profile using the auxiliary information and makes a recommendation to create it. It then enables the query optimizer (under normal mode) to generate a well-tuned plan. The most powerful aspect of SQL profiles is that they enable tuning of queries without requiring any syntactical changes and thereby proving a unique database –resident solution to tune the SQL statements embedded in packaged applications.
  • Access Path Analysis: The Automatic Tuning Optimizer considers whether a new index can be used to significantly improve access to each table in the query and when appropriate makes recommendations to create such indexes.
  • SQL Structure Analysis: The Automatic Tuning Optimizer tries to identify SQL statements that lend themselves to bad plans and makes relevant suggestions to restructure them. The suggested restructuring can be syntactic as well as semantic changes to the SQL code.
 自动调优优化器提出的调优建议可以被分为以下几类：
  • 统计信息分析：自动调优优化器将检查查询中使用的每个对象，如发现没有统计信息或信息过于陈旧，优化器将建议重新收集相关的统计信息。如果优化器的建议没有被执行，她还能自动地收集信息以补充缺失的统计信息或修正陈旧的统计信息。由于 Oracle 数据库能够自动地收集优化器所需的统计信息，通常此类问题不会出现，除非自动收集统计信息的功能被用户禁止。
  • SQL 档案（SQL Profiling）：自动调优优化器能够验证其调优结果，并收集额外信息修正调优结果中的错误。自动调优优化器还能依据 SQL 语句执行的历史情况，收集依据为一个 SQL 而定制的优化器设置信息（customized optimizer setting）（例如，首行（first rows）模式或所有行（all rows）模式）。自动调优优化器利用其收集的额外信息为 SQL 语句建立 SQL 档案。此时查询优化器（如运行在普通模式下）就可以使用 SQL 档案来生成执行计划了。用户使用 SQL 档案功能后，无需修改 SQL 语句也能对查询进行调优，这相当于将 SQL 语句的调优方案固化在数据库中，此功能有助于对预制的应用程序（packaged application）中的 SQL 语句进行调优。
  • 数据存取路径（Access Path）分析：自动调优优化器能够预测新的索引是否能显著提高查询中某个表的存取效率，如有可能将建议用户创建索引。
  • SQL 结构分析：自动调优优化器能够识别执行计划较差的 SQL 语句，并提出重构 SQL 语句的建议。自动调优优化器的建议既可能针对语法（syntactic），也可能针对语义（semantic）。
054 Both access path and SQL structure analysis can be useful in tuning the performance of an application under development or a homegrown production application where the administrators and developers have access to application code.
　		 如果应用程序正在开发，或者应用程序是自制的，管理员或开发者能够修改程序代码，那么可以采用数据存取路径分析或 SQL 结构分析对 SQL 语句进行调优。
　
055 The SQL Access Advisor can automatically analyze the schema design for a given workload and recommend indexes, function-based indexes, and materialized views to create, retain, or drop as appropriate for the workload. For single statement scenarios, the advisor only recommends adjustments that affect the current statement. For complete business workloads, the advisor makes recommendations after considering the impact on the entire workload.
　		 SQL 数据存取顾问工具（SQL Access Advisor）能够分析方案对象在某种工作负载下的数据访问情况，并在需要时向用户建议创建，保留，或移除索引，函数索引，物化视图等对象，以满足 此工作负载的需求。如果用户对一个单独语句进行调优，顾问工具在提出调优建议时只考虑对当前语句的影响。如果用户需要对整个系统的负载进行调优，顾问工具在提出调优建议时将考虑对整个系统的影响。
　
056 While generating recommendations, the SQL Access Advisor considers the impact of adding new indexes and materialized views on data manipulation activities, such as insert, update, and delete, in addition to the performance improvement they are likely to provide for queries. After the SQL Access Advisor has filtered the workload, but while it is still identifying all possible solutions, you can asynchronously interrupt the process to get the best solution up to that point in time.
　		 SQL 数据存取顾问工具在生成调优建议时，除了考虑调优对查询性能的提高之外，还会考虑添加了新数据库对象（例如索引或物化视图）后对插入，更新及删除等数据操作活动的影响。如果 SQL 数据存取顾问工具已经挑选出了数个执行计划，但仍在寻找其他可行的方案，用户可以异步地终止这个过程，并使用当前发现的最好的方案。
　
057 The SQL Access Advisor provides an easy to use interface and requires very little system knowledge. It can be run without affecting production systems, because the data can be gathered from the production system and taken to another computer where the SQL Access Advisor can be run.
　		 SQL 数据存取顾问工具拥有易用的用户接口，无需用户掌握大量的系统知识。SQL 数据存取顾问工具不会对生产系统产生很大的影响，因为用户可以将在生产系统中收集的数据迁移到其他安装了SQL 数据存取顾问工具的计算机上进行分析。
　
058

See Also:

Oracle Database Performance Tuning Guide for more information on the SQL Tuning Advisor and the SQL Access Advisor
另见：

Oracle Database Performance Tuning Guide 了解关于 SQL 调优顾问工具及 SQL 数据存取顾问工具的详细信息
059

Memory Management

14.5 内存管理
060 The System Global Area (SGA) is a shared memory region that contains data and control information for one Oracle instance. Automatic Shared Memory Management automates the management of SGA used by an Oracle Database instance. Simply specify the total amount of SGA memory available to an instance with the parameter SGA_TARGET. The Oracle Database then automatically distributes the available memory among various components as required.
　		 系统全局区（System Global Area，SGA）是一个共享的内存区域，其中包含了供 Oracle 实例使用的数据及控制信息。自动共享内存管理（Automatic Shared Memory Management）能使 Oracle 数据库实例 SGA 的管理自动化。用户只需通过 SGA_TARGET 参数为一个实例设定可供其 SGA 使用的总内存容量。Oracle 数据库能根据各个内存组件的需求自动地分配可用内存。
　
061 Oracle provides dynamic memory management that allows for resizing of the Oracle shared memory components dynamically. It also provides for transparent management of working memory for SQL execution by self-tuning the initialization runtime parameters controlling allocation of private memory. This helps users on systems with a low number of users to reduce the time and effort required to tune memory parameters for their applications, such as data warehouse and reporting applications. On systems with a higher number of users, this also allows them to avoid memory tuning for individual workloads.
　		 Oracle 具备动态内存管理功能，因此各个共享内存组件（shared memory component）的容量能够动态地调节。Oracle 还能自动调整用于控制私有内存（private memory）分配的运行时初始化参数（initialization runtime parameter），因此能够（对用户）透明地管理 SQL 语句执行时所需的工作内存区（working memory）。对于数据仓库或报表应用等用户较少的系统，上述功能可以大量减少用户手工调整应用程序内存参数的工作。对于用户数较多的系统，上述功能同样可以减少为每个用户连接调整内存的工作。
　
062 Oracle provides the following advisors to help size the memory allocation for optimal database performance.
　		 Oracle 提供了以下顾问工具来协助调整内存分配，以优化数据库性能。
　
063 The Shared Pool Advisor determines the optimal shared pool size by tracking its use by the library cache. The amount of memory available for the library cache can drastically affect the parse rate of an Oracle instance. The shared pool advisor statistics provide information about library cache memory, letting you predict how changes in the size of the shared pool can affect aging out of objects in the shared pool.
　		 共享池顾问工具（Shared Pool Advisor）通过跟踪库缓存（library cache）使用共享池的情况来决定最优的共享池容量。库缓存可用的内存容量决定了 Oracle 实例的解析（parse）效率。共享池顾问工具收集了关于库缓存的统计信息，供用户预测共享池的容量改变对共享池内对象保存时间的影响。
　
064 The Buffer Cache Advisor determines the optimal size of the buffer cache. When configuring a new instance, it is difficult to know the correct size for the buffer cache. Typically, you make a first estimate for the cache size, then run a representative workload on the instance and examines the relevant statistics to see whether the cache is under or over configured. A number of statistics can be used to examine buffer cache activity. These include the V$DB_CACHE_ADVICE view and the buffer cache hit ratio.
　		 数据库缓存顾问工具（Buffer Cache Advisor）的作用是决定数据库缓存的最优容量。当用户配置一个新的实例时，一般难以确定数据库缓存的最佳容量。通常，用户需要首先设置一个预估的容量，然后通过观察实例在预期负载下的统计信息来决定之前预估的容量是否适当。用户观察数据库缓存活动的统计指标有多个。例如 V$DB_CACHE_ADVICE 视图及数据库缓存命中率（buffer cache hit ratio）。
　
065 The Java Pool Advisor provides information about library cache memory used for Java and predicts how changes in the size of the Java pool can affect the parse rate.
　		 Java 池顾问工具（Java Pool Advisor）能够记录 Java 程序使用库缓存的情况，并预测改变 Java 池容量对解析效率的影响。
　
066 The Streams Pool Advisor determines the optimal size of the Streams pool. The view V$STREAMS_POOL_ADVICE gives estimates of the amount of bytes spilled and unspilled for the different values of the STREAMS_POOL_SIZE parameter. You can use this to tune the STREAMS_POOL_SIZE parameter for Streams and for logical standby. Automatic Workload Repository reports on the V$STREAMS_POOL_ADVICE view and CPU usage help you tune Streams performance.
　		 数据流池（Streams Pool Advisor）顾问工具能够决定数据流池的最佳容量。用户可以通过对 V$STREAMS_POOL_ADVICE 视图进行查询，了解 Oracle 预测的在各种 STREAMS_POOL_SIZE 参数值下数据流池的使用情况。用户依据视图中的信息为数据流及逻辑备用数据库（logical standby）设定 STREAMS_POOL_SIZE 参数。自动负载资料库（Automatic Workload Repository）能够提供基于数据流 CPU 使用情况和 V$STREAMS_POOL_ADVICE 视图的报表，协助用户调整数据流性能。
　
067 The Program Global Area (PGA) Advisor tunes PGA memory allocated to individual server processes. Under automatic PGA memory management mode, Oracle honors the PGA_AGGREGATE_TARGET limit by controlling dynamically the amount of PGA memory allotted to SQL database areas. At the same time, Oracle maximizes the performance of all the memory-intensive SQL operators by maximizing the number of database areas that are using an optimal amount of PGA memory (cache memory). The rest of the database areas are executed in one-pass mode, unless the PGA memory limit set by PGA_AGGREGATE_TARGET is so low that multipass execution is required to reduce even more the consumption of PGA memory and honor the PGA target limit.
　		 程序全局区顾问工具（Program Global Area Advisor）能够对每个服务进程（server process）的内存分配进行调整。在自动 PGA 内存管理模式下，Oracle 能够动态地控制为各个 SQL 工作区（database area）所分配的 PGA 内存容量，使其总 PGA 容量满足 PGA_AGGREGATE_TARGET 参数的限制。对于需要大量内存的 SQL 操作，Oracle 优先保证其工作区能够从 PGA 中分配足够的内存，从而保证这类操作的性能。Oracle 还将保证其余的工作区尽量工作在一次交换（one-pass）模式下。如果 PGA_AGGREGATE_TARGET 参数设置的过低，Oracle 将使某些工作区采取多次交换（multipass）的方式执行，从而减少 PGA 的消耗，确保 PGA 容量满足限制。
　
068 When configuring a new instance, it is difficult to know an appropriate setting for PGA_AGGREGATE_TARGET. You can determine this setting in three stages:
  1. Make a first estimate for PGA_AGGREGATE_TARGET.
  2. Run a representative workload on the instance and monitor performance using PGA statistics collected by Oracle to see whether the maximum PGA size is under configured or over configured.
  3. Tune PGA_AGGREGATE_TARGET using Oracle's PGA advice statistics.
 当用户配置新实例时，很难确定恰当的 PGA_AGGREGATE_TARGET 参数值。用户可以通过以下步骤使此参数更为合理：
  1. 首先估计一个 PGA_AGGREGATE_TARGET 参数值。
  2. 使实例运行在预期的负载下，通过 Oracle 收集的 PGA 统计信息来监控系统性能，从而决定当前参数值是否适当。
  3. 根据 PGA 顾问工具的统计数据来调整 PGA_AGGREGATE_TARGET 参数的值。
069 When the Automatic Shared Memory Management is enabled, the most commonly configured components are sized automatically. These include the following:
  • Shared pool (for SQL and PL/SQL execution)
  • Java pool for (Java execution state)
  • Large pool (for large allocations such as RMAN backup buffers)
  • Buffer cache
  • Streams pool
 当用户启用了自动共享内存管理后，需要用户经常调整容量的内存组件将被 Oracle 自动地调整。这样的内存组件包括：
  • 共享池（供 SQL 及 PL/SQL 执行适用）
  • Java 池（供 Java 程序执行适用）
  • 大型池（用于大量的内存分配，例如 RMAN 的备份缓冲区）
  • 数据库缓存
  • 数据流池
070 There is no need to set the of size any of these components explicitly, and by default the parameters for these components appear to have values of zero. Whenever a component needs memory, it can request that it be transferred from another component with the internal auto-tuning mechanism. This happens transparently without user-intervention.
　		 用户无需显式地为这些内存组件设定容量，默认情况下这些组件的容量参数均显示为 0。当某个内存组件需要扩展容量时，她将向系统发出请求，Oracle 则通过内部的自动调节机制将其他组件的内存转移给她。上述过程对用户是透明的。
　
071 The performance of each component is monitored by the Oracle instance. The instance uses internal views and statistics to determine how to optimally distribute memory among the automatically-sized components. Thus, as the workload changes, memory is redistributed to ensure optimal performance with the new workload. This algorithm tries to find the optimal distribution by taking into consideration long term and short terms trends.
　		 Oracle 组件负责监控各个内存组件的性能。实例根据内部视图的信息及其他统计信息来决定如何在各个自动管理的组件间分配内存以达到最优。这样，当工作负载改变时内存就能够被重新分配，从而确保系统在新负载下也能获得最优性能。内存分配调整算法会同时考虑系统运行的短期与长期趋势。
　
072 You can exercise some control over the size of the auto-tuned components by specifying minimum values for each component. This can be useful in cases where you know that an application needs a minimum amount of memory in certain components to function properly.
　		 对于自动管理的内存组件，用户可以为其指定最小容量。当用户了解其应用所需的各个内存组件的容量时，就可以使用此功能。
　
073 The sizes of the automatically-tuned components are remembered across shutdowns if a server parameter file (SPFILE) is used. This means that the system picks up where it left off from the last shutdown.
　		 如果数据库使用了服务器参数文件（server parameter file，SPFILE），那么自动调整内存组件的参数在实例关闭后依然能被保留。系统下次启动时可以使用上次关闭时保留的参数。
　
074 The most significant benefit of using automatic SGA memory management is that the sizes of the different SGA components are flexible and adapt to the needs of a workload without requiring user intervention. Besides maximizing the use of available memory, Automatic Shared Memory Management can enhance workload performance. With manual configuration, it is possible that the compiled SQL statements will frequently age out of the shared pool because of its inadequate size. This manifests into frequent hard parses and reduced performance. However, when automatic management is enabled, the internal tuning algorithm monitors the performance of the workload and grows the shared pool if it determines that doing so will reduce the number of parses required. This provides enhanced performance, without requiring any additional resources or manual tuning effort.
　		 使用自动 SGA 内存管理的最大好处是，各个 SGA 组件的容量是灵活可变的，能够适应不同的工作负载而无需用户干预。除了是可用内存最大化之外，自动共享内存管理还有助于提高系统性能。采用手工内存管理时，已编译的 SQL 语句可能会因为共享池容量不足而被清除出共享池。这将导致频繁的硬解析（hard parse）进而影响系统性能。而启用了自动内存管理后，内部调节算法将监控系统性能，如认为增大共享池有助于减少硬解析的话就会对内存组件做出相应调整。此功能提高了系统性能，且无需向系统添加资源，也无需任何手工 调整操作。
　
075

See Also:

另见：
076

Space Management

14.6 空间管理
077 The Oracle Database automatically manages its space consumption, sends alerts on potential space problems, and recommends possible solutions. Oracle features that help you to easily manage space include the following: Oracle 数据库能够自动地对其空间使用进行管理，能够发现潜在的空间问题，及时向管理员发出告警并给出可行的解决方案。Oracle 提供的协助用户对空间进行管理的功能有：
078

Automatic Undo Management

14.6.1 自动还原管理
079 Earlier releases of Oracle used rollback segments to store undo. Space management for these rollback segments was complex. Automatic undo management eliminates the complexities of managing rollback segments and lets you exert control over how long undo is retained before being overwritten. Oracle strongly recommends that you use undo tablespace to manage undo rather than rollback segments.
　		 之前版本的 Oracle 使用回滚段（rollback segment）来存储还原信息（undo）。回滚段的空间管理十分复杂。而采用自动还原管理（automatic undo management）将大大降低管理回滚段的复杂性，管理员只需专注于控制还原信息经过多长时间才能被覆盖即可。Oracle 强烈建议用户使用还原表空间（undo tablespace）来管理还原信息，而不要继续使用回滚段。
　
080 The Undo Advisor improves manageability of transaction management, especially for automatic undo management. The Undo Advisor presents the best retention possible for the given undo tablespace. It also advises a size for the undo tablespace when you want to set undo retention to a particular value.
　		 还原管理顾问工具（Undo Advisor）能够提高事物的可管理性，尤其是系统采用了自动还原管理时。还原管理顾问工具能够根据可用的还原表空间容量确定最佳的还原信息保存周期（undo retention）。还原管理顾问工具也能根据用户所需的还原信息保存周期建议最佳的还原表空间容量。
　
081 The Undo Advisor is based on system activity statistics, including the longest running query and undo generation rate. Advisor information includes the following:
  • Current undo retention
  • Current undo tablespace size
  • Longest query duration
  • Best undo retention possible
  • Undo tablespace size necessary for current undo retention
 还原管理顾问工具是依据系统运行的统计信息工作的，这些信息包括系统中执行时间最长的查询，还原信息生成率等。还原管理顾问工具能够提供的信息包括：
  • 当前的还原信息保存周期
  • 当前的还原表空间容量
  • 系统中最长的查询执行时间
  • 当前还原表空间容量所能提供的最大还原信息保存周期
  • 给定的还原信息保存周期所需的还原表空间容量
082

See Also:

另见：
083

Oracle-Managed Files

14.6.2 自动文件管理
084 With Oracle-managed files, you do not need to directly manage the files comprising an Oracle database. Oracle uses standard file system interfaces to create and delete files as needed. This automates the routine task of creation and deletion of database files.
　		 采用了自动文件管理（Oracle-managed file）后，用户无需直接管理组成 Oracle 数据库的各个文件。Oracle 能够使用标准的文件系统接口自动地创建或删除文件。这使数据库文件创建删除之类的常规管理工作能够自动地执行。
　
085

Free Space Management

14.6.3 可用空间管理
086 Oracle allows for managing free space within a table with bitmaps, as well as traditional dictionary based space management. The bitmapped implementation eliminates much space-related tuning of tables, while providing improved performance during peak loads. Additionally, Oracle provides automatic extension of data files, so the files can grow automatically based on the amount of data in the files. Database administrators do not need to manually track and reorganize the space usage in all the database files.
　		 Oracle 既可以使用位图（bitmap）来管理表的可用空间（free space），也可以使用传统的数据字典方式进行管理。采用位图方式对表的可用空间进行管理能够消除大量的空间调整工作，同时还能提高表在高负载下的工作性能。Oracle 还能够自动地扩展数据文件（data file），即数据文件的容量能够根据其中所存储的数据量而自动地增长。因此数据库管理员无需手工地监控所有数据文件的空间使用情况。
　
087

Proactive Space Management

14.6.4 主动空间管理
088 Oracle Database introduces a non-intrusive and timely check for space utilization monitoring. It automatically monitors space utilization during normal space allocation and de-allocation operations and alerts you if the free space availability falls below the pre-defined thresholds. Space monitoring functionality is set up out of box, causes no performance impact, and is uniformly available across all tablespace types. Also, the same functionality is available both through Enterprise Manager as well as SQL. Because the monitoring is performed at the same time as space is allocated and freed up in the database, this guarantees immediate availability of space usage information whenever you need it.
　		 Oracle 数据库能够定期地进行检查，从而实现对空间使用情况的监控，这种检查不会中断正常的数据库操作。Oracle 在空间分配及回收操作期间对系统的空间使用情况进行监控，如果发现可用空间低于预设的阈值将向用户发出告警。空间监控是 Oracle 的内置功能，因此不会对系统性能产生影响，且各种类型的表空间均可使用。用户通过企业管理器（Enterprise Manager）或 SQL 语句均可使用系统的空间监控功能。由于监控是与数据库空间分配及释放同时进行的，用户可以随时得到及时准确的空间使用情况。
　
089 Notification is performed using server-generated alerts. The alerts are triggered when certain space-related events occur in the database. For example, when the space usage threshold of a tablespace is crossed or when a resumable session encounters an out of space situation, then an alert is raised. An alert is sent instantaneously to take corrective measures. You may choose to get paged with the alert information and add space to the tablespace to allow the suspended operation to continue from where it left off.
　		 关于空间使用的信息是通过服务器告警（server-generated alert）通知给用户的。当数据库中发生的某些与空间使用相关的事件时，告警将被触发。例如，当某个表空间的已用空间超过了阈值，或一个可恢复会话（resumable session）遇到空间不足的状况，都会产生告警。告警信息能够被及时地传递给用户，以便用户采取适当的措施。例如，用户可以通过传呼（page）接受告警信息，再为表空间增加存储空间，使挂起的操作得以继续执行。
　
090 The database comes with a default set of alert thresholds. You can override the default for a given tablespace or set a new default for the entire database through Enterprise Manager.
　		 数据库内有一组默认的告警阈值。用户在企业管理器中可以为某个表空间单独设定特殊的阈值，也可以为整个数据库设定新的默认值。
　
091

Intelligent Capacity Planning

14.6.5 智能存储空间规划
092 Space may get overallocated because of the difficulty to predict the space requirement of an object or the inability to predict the growth trend of an object. On tables that are heavily updated, the resulting segment may have a lot of internal fragmentation and maybe even row chaining. These issues can result in a wide variety of problems from poor performance to space wastage. The Oracle Database offers several features to address these challenges.
　		 如果数据库对象所需的存储空间难以预测，或者对象容量的增长趋势难以预测，为某个数据库对象分配的空间很可能会过大。而频繁地进行更新操作的表，其数据段（segment） 中可能存在大量碎片（internal fragmentation）或行迁移（row chaining）。这些情况可能导致各种问题，例如存储性能下降或空间浪费。Oracle 数据库提供了多种解决此类问题的方法。
　
093 The Oracle Database can predict the size of a given table based on its structure and estimated number of rows. This is a powerful "what if" tool that allows estimation of the size of an object before it is created or rebuilt. If tablespaces have different extent management policies, then the tool will help decide the tablespace that will cause least internal fragmentation.
　		 Oracle 能够依据表结构及预计行数预测表的容量。用户可以在创建或重建对象之前使用这个强大的“what if”工具预测对象的容量。如果表空间可以使用不同的数据扩展（extent）管理策略，这个工具还能帮助用户决定采用哪种策略能够使数据段内的碎片最少。
　
094 The growth trend report takes you to the next step of capacity planning – planning for growth. Most database systems grow over time. Planning for growth is an important aspect of provisioning resources. To aid this process, the Oracle Database tracks historical space utilization in the AWR and uses this information to predict the future resource requirements.
　		 用户可以使用空间增长趋势报告（growth trend report）进一步地对空间进行规划——空间增长规划（planning for growth）。绝大多数数据库系统的容量都会随时间而增长。空间增长规划是资源供给（provisioning resource）的一个重要方面。Oracle 数据库在 AWR 中记录空间使用的历史信息，并以此为依据预测未来的资源需求，从而实现对空间增长的规划。
　
095

Space Reclamation

14.6.6 空间回收
096 The Oracle Database provides in-place reorganization of data for optimal space utilization by shrinking it. Shrinking of a segment makes unused space available to other segments in the tablespace and may improve the performance of queries and DML operations.
　		 Oracle 数据库能够对数据段（segment）进行收缩（shrinking）从而优化空间利用率，且执行收缩操作时无需额外空间（in-place）来重组数据。收缩操作可以释放数据段中的未用空间以供其他数据段使用，且能提高查询及 DML 操作的性能。
　
097 The segment shrink functionality both compacts the space used in a segment and then deallocates it from the segment. The deallocated space is returned to the tablespace and is available to other objects in the tablespace. Sparsely populated tables may cause a performance problem for full table scans. By performing shrink, data in the table is compacted and the high water mark of the segment is pushed down. This makes full table scans read less blocks run faster.
　		 执行数据段收缩（segment shrink）时，首先需要集中（compact）数据段内的数据，之后再释放段内的未用空间。从数据段中释放的空间将被返还给表空间，供表空间内的其他对象使用。如果表内的数据存储 的较为分散，将会影响全表扫描（full table scan）的性能。执行了收缩操作后，表内的数据将被集中，且数据段的高水位线（high water mark）将被降低。这将使全表扫描需要访问的数据块（block）更少，扫描更迅速。
　
098 Segment shrink is an online operation – the table being shrunk is open to queries and DML while the segment is being shrunk. Additionally, segment shrink is performed in place. This is an advantage over online table redefinition for compaction and reclaiming space. You can schedule segment shrink for one or all the objects in the database as nightly jobs without requiring any additional space to be provided to the database.
　		 数据段收缩属于联机操作，当表的数据段被收缩时，此表依然可以进行查询或 DML 操作。此外，数据段收缩无需额外的存储空间。本地收缩（in-place）与通过联机重定义（online table redefinition）的方式收缩相比更有优势。用户可以在夜间定期调度作业来执行数据库对象的收缩操作，而无需为数据库提供额外的存储空间。
　
099 Segment shrink works on heaps, IOTs, IOT overflow segments, LOBs, LOB segments, materialized views, and indexes with row movement enabled in tablespaces with automatic segment space management. When segment shrink is performed on tables with indexes on them, the indexes are automatically maintained when rows are moved around for compaction. User-defined triggers are not fired, however, because compaction is a purely physical operation and does not impact the application.
　		 在采用了自动段空间管理（automatic segment space management）的表空间中，数据段收缩可以作用于堆表（heap-organized table），索引表（index-organized table，IOT），索引表的行溢出段（Row Overflow Area），LOB 对象，LOB 段，物化视图，及允许行移动（row movement enabled）的索引。如果对带有索引的表进行数据段收缩操作，当数据行发生移动时 Oracle 能够自动地维护索引。但用户自定义的触发器不会被触发，因为数据段收缩属于物理操作，对应用程序没有影响。
　
100

Note:

Segment shrink can be performed only on tables with row movement enabled. Applications that explicitly track rowids of objects cannot be shrunk, because the application tracks the physical location of rows in the objects.

提示：

只有允许行移动的表才能够进行数据段收缩操作。如果应用程序中显示地使用了对象的 ROWID，那么这个对象就不能进行收缩，因为应用程序需要通过物理位置来定位对象内的数据行。
101 To easily identify candidate segments for shrinking, the Oracle Database automatically runs the Segment Advisor to evaluate the entire database. The Segment Advisor performs growth trend analysis on individual objects to determine if there will be any additional space left in the object in seven days. It then uses the reclaim space target to select candidate objects to shrink.
　		 Oracle 数据库能够自动地运行数据段顾问工具（Segment Advisor）对数据库进行评估，确定哪些数据段应该进行收缩操作。数据段顾问工具能够针对每个数据库对象进行容量增长趋势分析，预测数据库对象在七天之后是否依然存在可用空间。之后就可以对满足条件的对象进行数据段收缩以回收空间。
　
102

Note:

The Segment Advisor does not evaluate undo and temporary tablespaces.
提示：

数据段顾问工具不会评估还原表空间及临时表空间。
103 In addition to using the pre-computed statistics in the workload repository, the Segment Advisor performs sampling of the objects under consideration to refine the statistics for the objects. Although this operation is more resource intensive, it can be used to perform a more accurate analysis.
　		 数据段顾问工具除了可以使用 AWR 中已有的统计信息，也可以直接对对象进行采样使统计信息更为准确。这种操作将消耗大量系统资源，但能提供更为精确的分析结果。
　
104 Although segment shrink reduces row chaining, and the Oracle Database recommends online redefinition to remove chained rows, the Segment Advisor actually detects certain chained rows that are above a threshold. For example, if a row size increases during an update such that it not longer fits into the block, then the Segment Advisor recommends that the segment be reorganized to improve I/O performance.
　		 数据段收缩有助于减少行链接（row chaining），但 Oracle 建议采用对象联机重定义（online redefinition）来消除行链接。数据段顾问工具能够检测出某些超过阈值的行链接情况。例如，如果一个更新操作导致某行的容量超过了一个数据块的最大容量，数据段顾问工具将建议对数据段进行重组以提高 I/O 性能。
　
105

Note:

The Segment Advisor does not detect chained rows created by inserts.

提示：

数据段顾问工具无法检测插入操作导致的行链接。
106

See Also:

另见：
107

Storage Management

14.7 存储管理
108 Automatic Storage Management provides a vertical integration of the file system and volume manager specifically built for the Oracle database files. ASM distributes I/O load across all available resource to optimize performance while removing the need for manual I/O tuning (spreading out the database files avoids hotspots). ASM helps you manage a dynamic database environment by letting you grow the database size without having to shutdown the database to adjust the storage allocation.
　		 自动存储管理（Automatic Storage Management）将底层的文件系统（file system）及其上的卷管理器（volume manager）集成，用于管理 Oracle 的数据库文件。ASM 能够将 I/O 负载分布到所有可用的存储资源上，从而提高了系统性能且无需大量的手工 I/O 调整（即自动地将数据库文件分散从而避免出现热点（hotspot））。ASM 使用户能够增加数据库容量而无需关闭数据库，从而使数据库存储分配动态化。
　
109 Automatic Storage Management lets you define a pool of storage (called a disk group) and then the Oracle kernel manages the file naming and placement of the database files on that pool of storage. You can change the storage allocation (adding or removing disks) with SQL statements (CREATE DISKGROUP, ALTER DISKGROUP, and DROP DISKGROUP). You can also manage the disk groups with Enterprise Manager and the Database Configuration Assistant (DBCA).
　		 用户可以通过自动存储管理定义一个存储池（称为磁盘组（disk group）），Oracle 能够自动地基于存储池管理文件命名及文件存储位置。用户可以使用 SQL 语句（CREATE DISKGROUP，ALTER DISKGROUP，及 DROP DISKGROUP）改变存�