开个新贴，研究、探讨一下ORACLE AQ消息队列技术，欢迎大家介绍使用经验，如果没人参与，就做学习笔记。

没人响应，看来只能用来做学习笔记了

Overview of Streams
A、Oracle Streams enable information sharing
    这个是这个产品的主要目的吗？
B、Using Oracle Stream, each unit of shared iformation is called a message
    消息的定义？
C、The strem can propagate information within a database or from one database ot another.
    看来这个产品是依赖数据库的（不知道是否只有在ORACLE数据库里有这个概念）
D、Streams provides the capabilities needed to build and operate distributed enterprises and applications,data warehouses, and high availability solutions
    建立分布式企业应用、数据仓库、高可用性的解决方案
E、Streams informaiton flow
    Captue=>staging=>Consumption

What Can Streams Do?
A、Capture Messages at a Database
A cpature process can capture database events, such as changes made to tables,schemas,or an entire database.Such changes are recorded in the redo log for a database, and a capture process captures changes from the redo log and formats each captured change into a message called a logical change record(LCR). The rules used by a capture process determine which changes it captures, and these captured changes are called captured message
    第一个能作的就是捕获数据库中的消息

    捕获进程（capture process）捕获数据库中的改变，这种改变是记录在数据库REDO LOG日志中，（看来确实是依赖数据库的），至于捕获哪种改变（change），由规则（rule）决定
   
  这里有好多概念：
捕获进程（capture process）
逻辑改变记录（logical change record）
源数据库（The database where changes are generated in the redo log is called source database）
下游数据库（A capture process can capture changes locally at the source database ,or it can capture changes remotely at a downstream database）
用户队列消息（Users and applications can also enqueue messages into a queue manually.These messages are called user-enqueued messages）
还有显式捕获和隐式两种捕获（implicit capture/explicit capture）

What Can Streams Do?
B、Stage Messages in a Queue
在队列里储备消息
这里有些概念是成对出现的
队列类型：ANYDATA QUEUE和TYPED QUEUE
消息类型：CAPTURED MESSAGES和USER-ENQUEUED MESSAGES

What Can Streams Do?
C、Propagate Messages from One Queue to Another
传递消息
Streams propagations can propagate messages from one queue to another. These queues can be in the same database or in different databases .Rules determine which messages are propageated by a propagation

1、不同队列间消息传递
2、队列可以在同一个数据库中或不同数据库中
3、规则决定消息的传递策略

What Can Streams Do?
D、Consume Messages
A message is consumed when it is dequeued from a queue
从队列中取出消息的过程

这里也有几个概念
apply process <=> capture process

从队列中取消息可以是隐式的也可以是显式的

规则决定什么消息被APPLY PROCESS从队列中取出、处理

What Can Streams Do?
E、Other Capabilities of Streams

1、directed networks
    网络导向？数据传输的方向性，估计是说在消息传递过程中，定义规则，描述消息的路由，确定消息传送的目标地址
2、automatic conflict detection and conflict resolution
   自动冲突诊断和解决，这个有点夸张吧，估计是在网络中断的情况下，能够在数据库中缓存，当网络恢复时重新传输消息
3、rule-based transformations
   基于规则的传输转换，估计在这是使用这个东西的前提调价，规则制定是否复杂？未知
4、heterogeneous information sharing
   不同类型的消息信息共享，这个可能是跟ANYDATA QUEUE和TYPED QUEUE定义有关，不知道支持的数据类型是否丰富，如：一个XML是以文件形式传输还是流的形式，是自己解析消息吗？

What Are the Uses of Streams?
A、Message Queuing
Oracle Streams Advanced Queuing(AQ) enables user applications to eaqueue messages into a queue,propagate messages to subscribing queues, notify user applications that messages are ready for consumption,and dequeue messages at the destination.
重复描述消息队列的功能

A queue can be configured to stage messages of a particular type only,or aqueue can be configured as an ANYDATA queue. Messages of allmost any type can be wrapped in an ANYDATA wrapper and staged in ANYDATA queues.
看来这个ANYDATA类型的队列将应用的最多、最广泛了

What Are the uses of Streams?
B、Data Replication
Streams can capture DML and DDL changes made to database objects and replicate those changes to one or more other databases.A Streams capture process captures changes made to source database objects and formats them into LCRs, which can propagated to destination databases and then applied by Streams apply processes.
数据复制的基本方法，看来ORACLE数据库部署的STANDBY方式是利用Streams的基本技术实现的？