Database Instance Structure

When an instance is started, Oracle Database allocates a memory area called the system global area (SGA) and starts one or more background processes. The SGA serves various purposes, including the following:

• Maintaining internal data structures that are accessed by many processes and threads concurrently

• Caching data blocks read from disk

• Buffering redo data before writing it to the online redo log files

• Storing SQL execution plans

The SGA is shared by the Oracle processes, which include server processes and background processes, running on a single computer. The way in which Oracle processes are associated with the SGA varies according to operating system.

A database instance includes background processes. Server processes, and the process memory allocated in these processes, also exist in the instance. The instance continues to function when server processes terminate.

Oracle 实例结构

当实例启动时， Oracle 数据库分配一个叫做系统全局区（SGA） 的内存区域，并启动一个或多个后台进程。SGA 用于以下几个目的：

• 维护由很多进程和线程同时访问的内部数据结构
• 缓存从磁盘中读取的数据块
• 缓冲重做数据，然后再将其写入联机重做日志文件
• 存储 SQL 执行计划

SGA 由运行在一台单一计算机上的多个 Oracle 进程共享，包括服务器进程和后台进程。Oracle 进程与 SGA 相关联的方式会因不同的操作系统而有所不同。

数据库实例包括多个后台进程。服务器进程和在这些的进程中分配的进程内存也存在于实例中。当服务器进程终止时，实例仍会继续运行。

Figure 13-1 shows the main components of an Oracle database instance.

Figure 13-1 Database Instance

Description of "Figure 13-1 Database Instance"

Database Instance Configurations

You can run Oracle Database in either of the following mutually exclusive configurations:

• Single-instance configuration

  A one-to-one relationship exists between the database and an instance.

• Oracle Real Application Clusters (Oracle RAC) configuration

  A one-to-many relationship exists between the database and instances.

  数据库实例配置

  您可以在以下两种互斥配置中的一种来运行 Oracle 数据库：

  单实例配置

  数据库和实例之间存在一对一关系。

  Oracle 真正应用集群 （Oracle RAC）配置

  数据库与实例之间存在一对多关系。

Figure 13-2 shows possible database instance configurations.

图 13-2 显示了这两种可能的数据库实例配置。

Whether in a single-instance or Oracle RAC configuration, a database instance is associated with only one database at a time. You can start a database instance and mount (associate the instance with) one database, but not mount two databases simultaneously with the same instance.

Multiple instances can run concurrently on the same computer, each accessing its own database. For example, a computer can host two distinct databases:prod1 and prod2. One database instance manages prod1, while a separate instance manages prod2.

在同一台计算机上可以同时运行多个实例，每个实例访问其自己的数据库。

例如，一台计算机可以承载两个完全不同的数据库： prod1 和 prod2。一个数据库实例管理 prod1，而另一个实例管理 prod2。

Overview of Instance and Database Startup

In a typical use case, you manually start an instance and then mount and open the database, making it available for users. You can use the SQL*Plus STARTUPcommand, Oracle Enterprise Manager (Enterprise Manager), or the SRVCTL utility to perform these steps. Figure 13-3 shows how a database progresses from a shutdown state to an open state.

实例和数据库启动概述

A database goes through the following phases when it proceeds from a shutdown state to an open database state:

当数据库从关闭状态推进到打开状态时，会经历以下几个阶段：

1. Instance started without mounting database

   ?  1  启动实例，但未装载数据库

   The instance is started, but is not yet associated with a database.

   "How an Instance Is Started" explains this stage.

   实例已启动，但尚未与某个数据库相关联。"实例是如何启动的"解释了这一阶段。

    

2. Database mounted

   ?  2  装载数据库

   The instance is started and is associated with a database by reading its control file (see "Overview of Control Files"). The database is closed to users.

   "How a Database Is Mounted" explains this stage.

   实例已启动，并且通过读取控制文件，来与数据库相关联 （请参阅"控制文件概述"）。数据库对用户是关闭的。
   "数据库是如何装载的"解释了这一阶段。

3. Database open

   ?  3  打开数据库

   The instance is started and is associated with an open database. The data contained in the data files is accessible to authorized users.

   "How a Database Is Opened" explains this stage.

   
   

   实例已启动，并与一个打开的数据库相关联。授权的用户可以访问数据文件中包含的数据。

Overview of Database and Instance Shutdown

In a typical use case, you manually shut down the database, making it unavailable for users while you perform maintenance or other administrative tasks. You can use the SQL*Plus SHUTDOWN command or Enterprise Manager to perform these steps. Figure 13-4 shows the progression from an open state to a consistent shutdown.

举一个典型的使用案例，您手动关闭数据库以执行维护或其他管理任务，这将使数据库对用户不可用。您可以使用 SQL * Plus 的 SHUTDOWN 命令或企业管理器来执行这些步骤。图 13-4 显示从打开状态推进到一致关闭的过程。

Oracle Database automatically performs the following steps whenever an open database is shut down consistently:

当一致地关闭打开的数据库时，Oracle 数据库自动执行以下步骤：

1. Database closed

   数据库关闭

   The database is mounted, but online data files and redo log files are closed.

   数据库仍处于装载状态，但数据文件和联机重做日志文件已被关闭。

   "How a Database Is Closed" explains this stage.

   "数据库是如何关闭的"解释了这一阶段。

2. Database unmounted

   数据库卸载

   The instance is started, but is no longer associated with the control file of the database.

   实例仍处于启动状态，但已不再与数据库的控制文件相关联。

   "How a Database Is Unmounted" explains this stage.

   "数据库是如何卸载的"解释了这一阶段。

3. Database instance shut down

   数据库实例关闭

   The database instance is no longer started.

   数据库实例不再处于启动状态。

   "How an Instance Is Shut Down" explains this stage.

   "实例是如何关闭的"解释了这一阶段。

Oracle Database does not go through all of the preceding steps in an instance failure or SHUTDOWN ABORT, which immediately terminates the instance.

当实例失败或遭遇 SHUTDOWN ABORT 时，Oracle 数据库不会经历之前这些所有步骤，而只是立即终止该实例。

Purpose of Checkpoints

Oracle Database uses checkpoints to achieve the following goals:

Oracle 数据库使用检查点，来实现以下目标：

• Reduce the time required for recovery in case of an instance or media failure

  ?  减少实例失败或介质故障情况下恢复所需的时间

• Ensure that dirty buffers in the buffer cache are written to disk regularly

  ?  确保在缓冲区高速缓存中的脏缓冲区被定期写入磁盘

• Ensure that all committed data is written to disk during a consistent shutdown

  ?  确保在一致的关闭过程中所有已提交的数据都被写入磁盘

  
  

When Oracle Database Initiates Checkpoints

The checkpoint process (CKPT) is responsible for writing checkpoints to the data file headers and control file. Checkpoints occur in a variety of situations. For example, Oracle Database uses the following types of checkpoints:

检查点进程 （CKPT） 负责将检查点写入数据文件头和控制文件。检查点会在多种情况下发生。例如， Oracle 数据库使用以下类型的检查点：

• Thread checkpoints

  ?  线程检查点

  The database writes to disk all buffers modified by redo in a specific thread before a certain target. The set of thread checkpoints on all instances in a database is a database checkpoint. Thread checkpoints occur in the following situations:

  数据库将某个确定目标之前、被某个特定的重做线程所修改的所有缓冲区写入磁盘。数据库中所有实例的线程检查点的集合即为数据库检查点。线程检查点在下列情况下发生：

  • Consistent database shutdown

  • ALTER SYSTEM CHECKPOINT statement

  • Online redo log switch

  • ALTER DATABASE BEGIN BACKUP statement

    o  一致的数据库关闭

    o  ALTER SYSTEM CHECKPOINT 语句

    o  联机重做日志切换

    o  ALTER DATABASE BEGIN BACKUP 语句

• Tablespace and data file checkpoints

  ?  表空间和数据文件的检查点

  The database writes to disk all buffers modified by redo before a specific target. A tablespace checkpoint is a set of data file checkpoints, one for each data file in the tablespace. These checkpoints occur in a variety of situations, including making a tablespace read-only or taking it offline normal, shrinking a data file, or executing ALTER TABLESPACE BEGIN BACKUP.

  数据库将某个确定目标之前、被重做线程所修改的所有缓冲区写入磁盘。表空间检查点是一组数据文件检查点，每个数据文件检查点对表空间中的某个数据文件做检查点操作。这些检查点发生在很多情况下，包括将一个表空间变为只读、将表空间脱机、收缩数据文件、或执行 ALTER TABLESPACE BEGIN BACKUP 等。

• Incremental checkpoints

  ?  增量检查点

  An incremental checkpoint is a type of thread checkpoint partly intended to avoid writing large numbers of blocks at online redo log switches. DBWnchecks at least every three seconds to determine whether it has work to do. When DBWn writes dirty buffers, it advances the checkpoint position, causing CKPT to write the checkpoint position to the control file, but not to the data file headers.

  增量检查点是一种线程检查点，部分原因是为了避免在联机重做日志切换时写入大量的块。DBWn 至少每隔三秒会进行检查以确定是否有工作要做。当 DBWn 将脏缓冲区写入磁盘时, 它会向前推进检查点位置，导致 CKPT 将检查点位置写入控制文件，而不是数据文件头。

Other types of checkpoints include instance and media recovery checkpoints and checkpoints when schema objects are dropped or truncated.

其他类型的检查点包括实例和介质恢复检查点，和删除或截断模式对象时的检查点。

Purpose of Instance Recovery

Instance recovery ensures that the database is in a consistent state after an instance failure. The files of a database can be left in an inconsistent state because of how Oracle Database manages database changes.

实例恢复可确保数据库在一个实例失败后仍能回到一个一致的状态。由于Oracle 数据库对数据文件更改的管理方式所致，数据库的文件可以处于不一致的状态。

A redo thread is a record of all of the changes generated by an instance. A single-instance database has one thread of redo, whereas an Oracle RAC database has multiple redo threads, one for each database instance.

重做线程是对实例生成的所有更改的记录。单实例数据库拥有一个重做线程，而一个 Oracle RAC 数据库拥有多个重做线程——每个数据库实例有一个。

When a transaction is committed, log writer (LGWR) writes both the remaining redo entries in memory and the transaction SCN to the online redo log. However, the database writer (DBW) process writes modified data blocks to the data files whenever it is most efficient. For this reason, uncommitted changes may temporarily exist in the data files while committed changes do not yet exist in the data files.

当事务提交时，日志写入器 (LGWR) 将内存中的重做条目和事务 SCN 同时写入联机重做日志。但是，数据库写入器 (DBWn) 进程只在最有利的时机将已修改的数据块写入数据文件。由于这个原因，未提交的更改可能会暂时存在于数据文件中，而已提交的更改也可能还不在数据文件中。

If an instance of an open database fails, either because of a SHUTDOWN ABORT statement or abnormal termination, then the following situations can result:

如果某个打开的数据库的实例失败，或者由于 SHUTDOWN ABORT 语句或异常终止，则可能会导致下列情况：

• Data blocks committed by a transaction are not written to the data files and appear only in the online redo log. These changes must be reapplied to the database.

  ?  由某事务已提交的数据块更新还未写入数据文件，而仅写入了联机重做日志中。这些更改必须重新应用到数据库。

• The data files contains changes that had not been committed when the instance failed. These changes must be rolled back to ensure transactional consistency.

  ?  数据文件包含实例失败时尚未提交的更改。这些更改必须回滚，以确保事务一致性。

Instance recovery uses only online redo log files and current online data files to synchronize the data files and ensure that they are consistent.

实例恢复只使用联机重做日志文件和当前在线的数据文件，以同步数据文件，并确保它们一致。

When Oracle Database Performs Instance Recovery

Whether instance recovery is required depends on the state of the redo threads. A redo thread is marked open in the control file when a database instance opens in read/write mode, and is marked closed when the instance is shut down consistently. If redo threads are marked open in the control file, but no live instances hold the thread enqueues corresponding to these threads, then the database requires instance recovery.

是否需要实例恢复取决于重做线程的状态。在数据库实例被打开为读/写模式时，重做线程在控制文件中被标记为打开，而当实例被一致关闭时，重做线程被标记为关闭。如果重做线程在控制文件中被标记为打开，但没有活动的实例持有对应于这些线程的线程队列，则数据库将需要实例恢复。

Oracle Database performs instance recovery automatically in the following situations:

Oracle 数据库在以下情况下自动执行实例恢复：

• The database opens for the first time after the failure of a single-instance database or all instances of an Oracle RAC database. This form of instance recovery is also called crash recovery. Oracle Database recovers the online redo threads of the terminated instances together.

  ?  单实例数据库或 Oracle RAC 数据库的所有实例失败后第一次打开数据库。这种形式的实例恢复也称为崩溃恢复。Oracle 数据库一起恢复所有已终止实例的联机重做线程。

• Some but not all instances of an Oracle RAC database fail. Instance recovery is performed automatically by a surviving instance in the configuration.

  ?  只是 Oracle RAC 数据库中的某些、但不是所有实例失败。实例恢复将由配置中的某个存活实例自动进行。

The SMON background process performs instance recovery, applying online redo automatically. No user intervention is required.

SMON 后台进程自动执行实例恢复并应用联机重做记录。而不需要任何用户干预。

Importance of Checkpoints for Instance Recovery

Instance recovery uses checkpoints to determine which changes must be applied to the data files. The checkpoint position guarantees that every committed change with an SCN lower than the checkpoint SCN is saved to the data files.

实例恢复使用检查点来确定必须将哪些更改应用到数据文件。检查点位置始终保证所有比其 SCN 低的检查点所对应的已提交更改都已保存到数据文件。

Figure 13-5 depicts the redo thread in the online redo log.

图 13-5 描述了联机重做日志中的重做线程。

During instance recovery, the database must apply the changes that occur between the checkpoint position and the end of the redo thread. As shown in Figure 13-5, some changes may already have been written to the data files. However, only changes with SCNs lower than the checkpoint position are guaranteed to be on disk.

实例恢复期间，数据库必须应用检查点位置和重做线程结尾之间发生的更改。如图 13-5 所示， 某些更改可能已经写入数据文件。但是，只有其 SCN低于检查点位置的更改，才保证已被写到了磁盘上。

Instance Recovery Phases

The first phase of instance recovery is called cache recovery or rolling forward, and involves reapplying all of the changes recorded in the online redo log to the data files. Because rollback data is recorded in the online redo log, rolling forward also regenerates the corresponding undo segments.

实例恢复的第一阶段称为缓存恢复或前滚，这涉及将联机重做日志中记录的所有更改重新应用到数据文件。因为回滚数据记录在联机重做日志中，前滚也会重新生成相应的撤消段。

Rolling forward proceeds through as many online redo log files as necessary to bring the database forward in time. After rolling forward, the data blocks contain all committed changes recorded in the online redo log files. These files could also contain uncommitted changes that were either saved to the data files before the failure, or were recorded in the online redo log and introduced during cache recovery.

前滚会遍历各个必要的联机重做日志，以将数据库推进到一个更前的一致时间点。前滚之后，数据块包含记录在联机重做日志文件中的所有已提交更改。这些文件可能还包含未提交的更改，要么是在实例失败前保存到数据文件中的，或者是在缓存恢复过程中引入的。

After the roll forward, any changes that were not committed must be undone. Oracle Database uses the checkpoint position, which guarantees that every committed change with an SCN lower than the checkpoint SCN is saved on disk. Oracle Database applies undo blocks to roll back uncommitted changes in data blocks that were written before the failure or introduced during cache recovery. This phase is called rolling back or transaction recovery.

前滚之后，任何未提交的更改必须被撤消。Oracle 数据库使用检查点位置，保证每个低于其 SCN 的已提交更改都已保存到磁盘。Oracle 数据库应用撤消块，以回滚数据块中在实例失败前写入的或缓存恢复过程中引入的未提交更改。这一阶段称为回滚或事务恢复。

Figure 13-6 illustrates rolling forward and rolling back, the two steps necessary to recover from database instance failure.

图 13-6 说明了前滚和回滚，这是恢复数据库实例失败的两个必要步骤。

Figure 13-6 Basic Instance Recovery Steps: Rolling Forward and Rolling Back

图 13-6 基本的实例恢复步骤： 前滚和回滚

Description of "Figure 13-6 Basic Instance Recovery Steps: Rolling Forward and Rolling Back"

Oracle Database can roll back multiple transactions simultaneously as needed. All transactions that were active at the time of failure are marked as terminated. Instead of waiting for the SMON process to roll back terminated transactions, new transactions can roll back individual blocks themselves to obtain the required data.

Oracle 数据库可以根据需要同时回滚多个事务。实例失败时的所有活动事务被标记为终止。新事务可以自己回滚个别块以获取所需的数据，而不必等待 SMON 进程来回滚这些已终止的事务。

Initialization Parameters

Initialization parameters are configuration parameters that affect the basic operation of an instance. The instance reads initialization parameters from a file at startup.

初始化参数是会影响实例基本操作的配置参数。实例在启动时从一个文件读取初始化参数。

Oracle Database provides many initialization parameters to optimize its operation in diverse environments. Only a few of these parameters must be explicitly set because the default values are adequate in most cases.

Oracle 数据库提供了许多初始化参数，以优化其在不同环境中的操作。只需要显式设置几个参数，因为其默认值对大多数情况已经足够。

Server Parameter Files

A server parameter file is a repository for initialization parameters that is managed by Oracle Database. A server parameter file has the following key characteristics:

服务器参数文件是 Oracle 数据库用来管理初始化参数的一个存储库。服务器参数文件具有以下主要特征：

• Only one server parameter file exists for a database. This file must reside on the database host.

  ?  对于一个数据库，只存在一个服务器参数文件。此文件必须驻留在数据库主机上。

• The server parameter file is written to and read by only by Oracle Database, not by client applications.

  ?  服务器参数文件只由 Oracle 数据库读取和写入，而不能由客户端应用程序读取和写入。

• The server parameter file is binary and cannot be modified by a text editor.

  ?  服务器参数文件是二进制的，且不能使用文本编辑器修改。

• Initialization parameters stored in the server parameter file are persistent. Any changes made to the parameters while a database instance is running can persist across instance shutdown and startup.

  ?  存储在服务器参数文件中的初始化参数是永久性的。数据库实例正在运行时对参数所做的任何更改，可以跨实例关闭和启动而存在。

A server parameter file eliminates the need to maintain multiple text initialization parameter files for client applications. A server parameter file is initially built from a text initialization parameter file using the CREATE SPFILE statement. It can also be created directly by the Database Configuration Assistant.

服务器参数文件消除了为多个客户端应用程序维护多个文本初始化参数文件的需要。服务器参数文件最初可以从一个文本初始化参数文件，使用CREATE SPFILE 语句来生成。也可以直接由数据库配置助手创建。

Text Initialization Parameter Files

A text initialization parameter file is a text file that contains a list of initialization parameters. This type of parameter file, which is a legacy implementation of the parameter file, has the following key characteristics:

文本初始化参数文件是一个文本文件，其中包含初始化参数的列表。这是一种旧式参数文件，具有以下关键特征：

• When starting up or shutting down a database, the text initialization parameter file must reside on the same host as the client application that connects to the database.

  ?  当启动或关闭数据库时，文本初始化参数文件必须驻留在连接到该数据库的客户端应用程序相同的主机上。

• A text initialization parameter file is text-based, not binary.

  ?  文本初始化参数文件是基于文本的，而非二进制。

• Oracle Database can read but not write to the text initialization parameter file. To change the parameter values you must manually alter the file with a text editor.

  ?  Oracle 数据库可以读取，但不能写入文本初始化参数文件。若要更改参数值，必须使用文本编辑器手动更改文件。

• Changes to initialization parameter values by ALTER SYSTEM are only in effect for the current instance. You must manually update the text initialization parameter file and restart the instance for the changes to be known.

  ?  通过 ALTER SYSTEM 对初始化参数值所做的更改，仅在当前实例中有效。您必须手动更新文本初始化参数文件，并重新启动实例以使更改生效。

The text initialization parameter file contains a series of key=value pairs, one per line. For example, a portion of an initialization parameter file could look as follows:

文本初始化参数文件包含一系列 key=value 对，每行一个。例如，某个初始化参数文件中的一部分看起来如下所示： 

To illustrate the manageability problems that text parameter files can create, assume that you use computers clienta and clientb and must be able to start the database with SQL*Plus on either computer. In this case, two separate text initialization parameter files must exist, one on each computer, as shown inFigure 13-7. A server parameter file solves the problem of the proliferation of parameter files.

为了说明文本参数文件可能产生的可管理性问题，假定您使用计算机clienta 和 clientb，并且必须能够从其中任何一台计算机上使用 SQL*Plus 启动数据库。在这种情况下，必须存在两个独立的文本初始化参数文件，每台计算机上一个，如图 13-7 所示。服务器参数文件解决了分散的参数文件问题。

Figure 13-7 Multiple Initialization Parameter Files

图 13-7 多个初始化参数文件

Description of "Figure 13-7 Multiple Initialization Parameter Files"

Modification of Initialization Parameter Values

You can adjust initialization parameters to modify the behavior of a database. The classification of parameters as static or dynamic determines how they can be modified. Table 13-3 summarizes the differences.

您可以修改初始化参数，以调整数据库行为。将其按静态或动态参数的分类，确定了应如何修改它们。表 13-3 总结了的其中的差异。

Static parameters include DB_BLOCK_SIZE, DB_NAME, and COMPATIBLE. Dynamic parameters are grouped into session-level parameters, which affect only the current user session, and system-level parameters, which affect the database and all sessions. For example, MEMORY_TARGET is a system-level parameter, while NLS_DATE_FORMAT is a session-level parameter (see "Locale-Specific Settings").

静态参数包括 DB_BLOCK_SIZE、DB_NAME 、和 COMPATIBLE 等。动态参数可分为会话级参数和系统级参数，会话级参数只影响当前的用户会话，而系统级参数影响数据库及所有会话。例如，MEMORY_TARGET 是一个系统级参数，而 NLS_DATE_FORMAT 是一个会话级参数 （请参见"特定于区域的设置"）。

The scope of a parameter change depends on when the change takes effect. When an instance has been started with a server parameter file, you can use the ALTER SYSTEM SET statement to change values for system-level parameters as follows:

参数更改的范围取决于更改何时生效。若实例是用服务器参数文件启动的，则可以使用 ALTER SYSTEM SET 语句更改系统级参数的值，如下所示：

• SCOPE=MEMORY

  Changes apply to the database instance only. The change will not persist if the database is shut down and restarted.

  更改只应用于数据库实例。如果数据库关闭并重新启动，更改将不会保留。 

• SCOPE=SPFILE

  Changes are written to the server parameter file but do not affect the current instance. Thus, the changes do not take effect until the instance is restarted.

  更改被写入服务器参数文件，但不会影响当前实例。因此，所做的更改不会生效，直到重新启动该实例。

  Note:

  You must specify SPFILE when changing the value of a parameter described as not modifiable in Oracle Database Reference.
  当你修改某个在《Oracle 数据库参考》中描述为不可修改的参数的值时，必须指定 SPFILE。

• SCOPE=BOTH

  Changes are written both to memory and to the server parameter file. This is the default scope when the database is using a server parameter file.

  将更改同时写入内存和服务器参数文件。当数据库使用服务器参数文件时，这是默认的范围。

The database prints the new value and the old value of an initialization parameter to the alert log. As a preventative measure, the database validates changes of basic parameter to prevent illegal values from being written to the server parameter file.

数据库会在警报日志中输出初始化参数的旧值和新值。作为一项预防措施，数据库会验证对基本参数的更改，以防止非法值被写入到服务器参数文件中。

Automatic Diagnostic Repository

Automatic Diagnostic Repository (ADR) is a file-based repository that stores database diagnostic data such as trace files, the alert log, and Health Monitor reports. Key characteristics of ADR include:

自动诊断存储库 （ADR） 是一个基于文件的存储库，存储了如跟踪文件、警报日志、和健康监测报告等数据库诊断数据。ADR 的关键特征包括：

• Unified directory structure

• Consistent diagnostic data formats

• Unified tool set

  ?  统一的路径结构

  ?  一致的诊断数据格式

  ?  统一的工具集

The preceding characteristics enable customers and Oracle Support to correlate and analyze diagnostic data across multiple Oracle instances, components, and products.

上述特性使得客户和 Oracle 支持部门能跨多个 Oracle 实例、 组件、和产品对诊断数据进行关联和分析。

ADR is located outside the database, which enables Oracle Database to access and manage ADR when the physical database is unavailable. An instance can create ADR before a database has been created.

ADR 处于数据库之外，这使得即便物理数据库不可用时，也可以访问和管理 ADR。在创建数据库之前，其实例就可以创建 ADR。

ADR Structure

ADR 结构

The ADR base is the ADR root directory. The ADR base can contain multiple ADR homes, where each ADR home is the root directory for all diagnostic data—traces, dumps, the alert log, and so on—for an instance of an Oracle product or component. For example, in an Oracle RAC environment with shared storage and ASM, each database instance and each ASM instance has its own ADR home.

ADR base 是 ADR 的根目录。ADR base 可能包含多个 ADR home，每个ADR home 是一个 Oracle 产品或组件实例的所有的诊断数据的根目录，包括跟踪、 转储、 和警报日志等等。例如，在有共享存储和 ASM 的 Oracle RAC 环境中，每个数据库实例和每个 ASM 实例都有自己的 ADR Home。

Figure 13-8 illustrates the ADR directory hierarchy for a database instance. Other ADR homes for other Oracle products or components, such as ASM or Oracle Net Services, can exist within this hierarchy, under the same ADR base.

图 13-8 说明了数据库实例的 ADR 目录层次结构。其他 Oracle 产品或组件（如 ASM 或 Oracle 网络服务）的 ADR Home 也可以存在于此层次结构中，在相同的 ADR base 之下。

Figure 13-8 ADR Directory Structure for an Oracle Database Instance

Description of "Figure 13-8 ADR Directory Structure for an Oracle Database Instance"

As the following Linux example shows, when you start an instance with a unique SID and database name before creating a database, Oracle Database creates ADR by default as a directory structure in the host file system. The SID and database name form part of the path name for files in the ADR Home.

如下的 Linux 示例显示， 当你在创建一个数据库之前，使用一个唯一的 SID 和数据库名称启动一个实例时，Oracle 数据库在主机文件系统中会将 ADR默认创建为一个目录结构。SID 和数据库名称形成 ADR Home 中的文件路径名称的一部分。

Example 13-1 Creation of ADR

% setenv ORACLE_SID osi

% echo "DB_NAME=dbn" > init.ora

% sqlplus / as sysdba

.

.

.

Connected to an idle instance.

 

SQL> STARTUP NOMOUNT PFILE="./init.ora"

ORACLE instance started.

 

Total System Global Area  146472960 bytes

Fixed Size                  1317424 bytes

Variable Size              92276176 bytes

Database Buffers           50331648 bytes

Redo Buffers                2547712 bytes

 

SQL> SELECT NAME, VALUE FROM V$DIAG_INFO;

 

NAME                  VALUE

--------------------- --------------------------------------------------

Diag Enabled          TRUE

ADR Base              /u01/oracle/log

ADR Home              /u01/oracle/log/diag/rdbms/dbn/osi

Diag Trace            /u01/oracle/log/diag/rdbms/dbn/osi/trace

Diag Alert            /u01/oracle/log/diag/rdbms/dbn/osi/alert

Diag Incident         /u01/oracle/log/diag/rdbms/dbn/osi/incident

Diag Cdump            /u01/oracle/log/diag/rdbms/dbn/osi/cdump

Health Monitor        /u01/oracle/log/diag/rdbms/dbn/osi/hm

Default Trace File    /u01/oracle/log/diag/rdbms/dbn/osi/trace/osi_ora_10533.trc

Active Problem Count  0

Active Incident Count 0

The following sections describe the contents of ADR.

以下各节描述了 ADR 的内容。

Alert Log

Each database has an alert log, which is an XML file containing a chronological log of database messages and errors. The alert log contents include the following:

每个数据库都有一个警报日志，它是一个 XML 文件，其中包含按时间排序的数据库信息和错误的日志。警报日志的内容包括如下：

• All internal errors (ORA-600), block corruption errors (ORA-1578), and deadlock errors (ORA-60)

  ?  所有的内部错误 (ORA-600)、 块损坏错误 （ORA-1578) 、和死锁错误 (ORA-60)

• Administrative operations such as DDL statements and the SQL*Plus commands STARTUP, SHUTDOWN, ARCHIVE LOG, and RECOVER

  
  

  ?  管理性操作，如 DDL 语句和 STARTUP、SHUTDOWN、ARCHIVELOG、和 RECOVER 等 SQL*Plus 命令

• Several messages and errors relating to the functions of shared server and dispatcher processes

  ?  几个与共享服务器和调度器进程的功能有关的消息和错误

• Errors during the automatic refresh of a materialized view

  ?  物化视图自动刷新过程中的错误

Oracle Database uses the alert log as an alternative to displaying information in the Enterprise Manager GUI. If an administrative operation is successful, then Oracle Database writes a message to the alert log as "completed" along with a time stamp.

Oracle 数据库使用警报日志作为在企业管理器 GUI 中显示信息的一种替代。如果管理操作成功，则 Oracle 数据库向警报日志写入一条带有时间戳的“已完成”消息。

Oracle Database creates an alert log in the alert subdirectory shown in Figure 13-8 when you first start a database instance, even if no database has been created yet. The following example shows a portion of a text-only alert log:

如图 13-8 所示， 当您首次启动一个数据库实例，即使其数据库尚未创建，Oracle 数据库会在 alert 子目录中创建一个警报日志。下面的示例演示一个纯文本警报日志的一部分：

As shown in Example 13-1, query V$DIAG_INFO to locate the alert log.

如例 13-1 所示，通过查询 V$DIAG_INFO 来定位警报日志。

Trace Files

A trace file is an administrative file that contain diagnostic data used to investigate problems. Also, trace files can provide guidance for tuning applications or an instance, as explained in "Performance Diagnostics and Tuning".

跟踪文件是一个管理性文件，其中包含用于调查问题的诊断数据。此外，跟踪文件也可以为优化应用程序或实例提供指导，如"性能诊断与调整"所述。