Oracle APEX，以前称为 HTML DB，是一个集成在 Oracle 数据库中的快速 Web 应用开发工具。“集成在 Oracle 数据库中”是 Oracle APEX 的一个非常重要的特点，它意味着只要是安装了 Oracle 数据库，那么你就拥有了使用 Oracle APEX 开发 Web 应用的充分条件（当然了，你还需要一个浏览器来作为客户端）。另外，Oracle APEX 是 Oracle 数据库的一个默认组件，那么“它的生命周期完全和数据库等同，因而可以保证时间上的投入不会很快过时。此外，对于很多非 IT 企业而言，几乎可以完全摆脱对第三方 Web 应用开发商的依赖。默认的 Theme 已经可以满足绝大部分需求，只需要少量的修改，即可媲美专业网站。不论从员工价值提升，还是企业管理成本上说，都非常有益。”

稍微了解一下 Oracle APEX 的架构就可以知道，它与 Oracle 数据库的结合之紧密。原来所有的 Web 页面都是通过 Oracle APEX 引擎读取和渲染存储在数据库表中的数据而来。而当你建立或者扩展一个应用时，Oracle APEX 则将建立或者修改相应的元数据到数据库表中，而当应用运行时，Oracle APEX 又将负责读取元数据和显示。令人惊讶的是，甚至连 Oracle APEX 自身也不过是由数据库中的 215+ 的表和 200+ 的 PL/SQL 对象所组成。

而由 Oracle APEX 的架构，我们也不难想象，为什么使用 Oracle APEX 来开发 Web 应用程序，所需的只是基本的 HTML、Javascript 和 SQL、PL/SQL 知识，由此也可见 Oracle APEX 的学习门槛是非常低的。

参考（英文）：

What is Oracle Application Express?

Oracle Application Express 文档

DB_FLASHBACK_RETENTION_TARGET specifies the upper limit (in minutes) on how far back in time the database may be flashed back. How far back one can flashback a database depends on how much flashback data Oracle has kept in the flash recovery area.

By default, the change tracking file is created as an Oracle managed file in DB_CREATE_FILE_DEST.

Oracle Database provides database resource management capability through its Database Resource Manager. The main goal of the Database Resource Manager is to give the Oracle Database server more control over resource management decisions, thus circumventing problems resulting from inefficient operating system management.

DBVERIFY is an external command-line utility that performs a physical data structure integrity check. It can be used on offline or online databases, as well on backup files. You use DBVERIFY primarily when you need to ensure that a backup database (or datafile) is valid before it is restored, or as a diagnostic aid when you have encountered data corruption problems.

You must have a flash recovery area enabled, because flashback logs can only be stored in the flash recovery area. For Real Application Clusters databases, the flash recovery area must be stored in a clustered file system or in ASM.

When flashback is enabled or when there are guaranteed restore points, the background process RVWR writes flashback data to flashback database logs in the flash recovery area.

Database Resource Manager (DRM) allocates resources among resource consumer groups based on a resource plan. A resource plan consists of resource plan directives that specify how resources should be distributed among the groups. Resource consumer groups are categories to which user sessions can be assigned. These groups can then be allocated resources through plan directives.

WITH GRANT OPTION
Specify WITH GRANT OPTION to enable the grantee to grant the object privileges to other users and roles.

Use the MERGE statement to select rows from one or more sources for update or insertion into a table or view. You can specify conditions to determine whether to update or insert into the target table or view.

An inconsistent backup, also known as an online backup, is performed while the database is open and available to users. The backup is inconsistent because the SCN in the control file is most likely out of synch with the SCN in the header of the datafiles. Inconsistent backups require recovery when they are used for recovering from a media failure, but keep availability high because the database is open while the backup is performed.

REMAP_SCHEMA=source_schema:target_schema

Loads all objects from the source schema into a target schema.

As you can see from above screenshot of MetaLink, 11.1.0.7.0 Patch Set for ORACLE Database Server for HP-UX Itanium is released on 06-OCT-2008.

And I’m so proud to make contribution to this release. Cheers!

V$SYSTEM_EVENT视图显示了数据库实例（instance）启动以来所有会话（session）所遇到的所有等待事件的累计统计信息（aggregated statistics）。

SQL> desc v$system_event
Name                                      Null?    Type
—————————————– ——– —————————-
EVENT                                              VARCHAR2(64)
TOTAL_WAITS                                  NUMBER
TOTAL_TIMEOUTS                            NUMBER
TIME_WAITED                                   NUMBER
AVERAGE_WAIT                                 NUMBER
TIME_WAITED_MICRO                       NUMBER
TOTAL_WAITS_FG                              NUMBER
TOTAL_TIMEOUTS_FG                        NUMBER
TIME_WAITED_FG                               NUMBER
AVERAGE_WAIT_FG                            NUMBER
TIME_WAITED_MICRO_FG                   NUMBER
EVENT_ID                                           NUMBER
WAIT_CLASS_ID                                  NUMBER
WAIT_CLASS#                                      NUMBER
WAIT_CLASS                                       VARCHAR2(64)

其中EVENT列包含了等待事件的名称，TOTAL_WAITS列包含了会话等待该事件的次数。TIME_WAITED显示了等待该事件所花费的总时间。

V$SESSION_EVENT视图

V$SESSION_EVENT视图显示了当前连接到实例上的所有会话的等待事件的累计统计信息。

SQL> desc v$session_event
Name                                      Null?    Type
—————————————–
SID                                                   NUMBER
EVENT                                              VARCHAR2(64)
TOTAL_WAITS                                  NUMBER
TOTAL_TIMEOUTS                            NUMBER
TIME_WAITED                                   NUMBER
AVERAGE_WAIT                                 NUMBER
MAX_WAIT                                         NUMBER
TIME_WAITED_MICRO                        NUMBER
EVENT_ID                                          NUMBER
WAIT_CLASS_ID                                 NUMBER
WAIT_CLASS#                                     NUMBER
WAIT_CLASS                                      VARCHAR2(64)

V$EVENT_NAME视图并不是一个动态视图，它的内容不会随着时间的推移而变化。它是一个包含了你的数据库实例所定义的所有等待事件（wait events）的名字的参考视图。等待事件的数量随着数据库版本的不同而不同，并且也依赖于所安装的数据库选项（option）：

$ sqlplus / as sysdba

SQL*Plus: Release 11.1.0.6.0 – Production on Tue Sep 23 01:33:39 2008

Copyright (c) 1982, 2007, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 – 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options

SQL> desc v$event_name
Name                                      Null?    Type
—————————————–
EVENT#                                             NUMBER
EVENT_ID                                          NUMBER
NAME                                                VARCHAR2(64)
PARAMETER1                                     VARCHAR2(64)
PARAMETER2                                     VARCHAR2(64)
PARAMETER3                                     VARCHAR2(64)
WAIT_CLASS_ID                                 NUMBER
WAIT_CLASS#                                    NUMBER
WAIT_CLASS                                      VARCHAR2(64)

SQL> select count(*) from v$event_name;

COUNT(*)
———-
961

一个简单的COUNT(*)就可以告诉你你的数据库中定义了多少个等待事件。

每个等待事件拥有最多3个属性（attributes），它们分别被记录在PARAMETER1，PARAMETER2和PARAMETER3列中。同时，这3列的值也将会显示在V$SESSION_WAIT视图的P1TEXT，P2TEXT和P3TEXT列中。

This year, there are 4 members of our group (in OARDC Shenzhen) have the opportuinity to participate this world’s largest conference for Oracle customers and technologists. But for me, I think I have to wait for OpenWorld 2009 or 2010

最近尝试了一下将Oracle Clusterware 11gR1的OCR和VD放在OCFS2上，这里记录一下OCFS2的安装过程。

首先是确定所使用的Linux的发行版本（distribution），内核版本（version）和风格（flavor），处理器架构：

# cat /etc/redhat-release
Enterprise Linux Enterprise Linux AS release 4 (October Update 5)

# uname -r
2.6.9-67.0.4.0.2.ELsmp

# uname -p
i686

可以看到这里我使用的是Oracle Enterprise Linux 4u5（可以认为是等同于Red Hat Enterprise Linux 4u5），内核版本是2.6.9-67.0.4.0.2，内核风格是smp，处理器架构是i686（也就是x86）。

接下来按照上面的信息去下载相应的OCFS2和OCFS2 Tools（包括ocfs2-tools和ocfs2console）的RPM包。

# wget -c http://oss.oracle.com/projects/ocfs2/dist/files/RedHat/RHEL4/i386/1.2.9-1/2.6.9-67.0.4.EL/ocfs2-2.6.9-67.0.4.ELsmp-1.2.9-1.el4.i686.rpm
# wget -c http://oss.oracle.com/projects/ocfs2-tools/dist/files/RedHat/RHEL4/i386/1.2.7-1/ocfs2-tools-1.2.7-1.el4.i386.rpm
# wget -c http://oss.oracle.com/projects/ocfs2-tools/dist/files/RedHat/RHEL4/i386/1.2.7-1/ocfs2console-1.2.7-1.el4.i386.rpm

删除掉现有的老版本的OCFS2相关RPM包：

# rpm -qa | grep ocfs | xargs rpm -e

依次安装刚刚下载的3个RPM：

# rpm -ivh ocfs2-tools-1.2.7-1.el4.i386.rpm
# rpm -ivh ocfs2console-1.2.7-1.el4.i386.rpm
# rpm -ivh --nodeps ocfs2-2.6.9-67.0.4.ELsmp-1.2.9-1.el4.i686.rpm

注意安装OCFS2 RPM时需要加上“–nodeps”选项。

这里还有一个问题，上面安装的OCFS2 RPM的内核版本（2.6.9-67.0.4）与我所使用的Linux的内核版本（2.6.9-67.0.4.0.2）并不完全一致，所以还需要进行下面的额外工作：

# cp -r /lib/modules/2.6.9-67.0.4.ELsmp/kernel/fs/* /lib/modules/2.6.9-67.0.4.0.2.ELsmp/kernel/fs

至此，OCFS2的安装已经完成。

Complete product portfolio

Open

Open standard and open source

Integrated

Integrated products

You can manage primary and standby databases using the SQL command-line interface or the Data Guard broker interfaces, including a command-line interface DGMGRL and a graphical user interface that is integrated in Oracle Enterprise Manager.

Primay Database

A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.

The primary database can be either a single-instance Oracle database or an Oracle Real Application Clusters (RAC) database.

Standby Databases

A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to 9 standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.

Similar to a primary database, a standby database can be either a single-instance Oracle database or an Oracle RAC database.

The types of standby databases are as follows:

• Physical standby database
• Logical standby database
• Snapshot standby database