Introduction to oracle rac

一、Overview of rac 2

二、overview of oracle clusterware for oracle rac 3

三、 Overview of Oracle RAC Architecture and Processing 3

1、clusterware storage solutions 3

2、 services and vip address 3

3、 About Oracle RAC Software Components 4

4、 About Oracle RAC Background Processes 4

四、 Overview of Automatic Workload Management 4

五、 Overview of installing oracle rac 4

六、 Overview of managing oracle rac environments 4

Oracle rac 使用oracle clusterware作为infrastructure来绑定多server，使这些server像一个单一的系统一样运作。Oracle clusterware 可以使noncluster oracle databases 和oracle rac database使用oracle high-availability infrastructure. （noncluster oracle database数据库的实例之间只一对一的关系，而rac中是一对多的关系） 

一、Overview of rac   

每一个oracle rac 的实例必须有

（1）At least one additional thread of redo for each instance

（2）An instance-specific undo tablespace

二、overview of oracle clusterware for oracle rac 

Oracle clusterware 为所有oracle database 平台提供一个完整的，集成的clusterware管理方案。该clusterware为cluster database提供各种管理包括node membership,group services,global resource management,high availability functions.  You can install Oracle Clusterware independently or as a prerequisite to the Oracle RAC installation process。

Oracle clusterware daemons运行在每个节点上。

Oracle clusterware 有两个组件：一个是the voting disk files 记录node membership information, 一个是oracle cluster registry （OCR）记录cluster的配置信息。Voting disks 和OCRs必须存储在shared storage中，available to all cluster member nodes.

1、CRS resource：

Oracle Clusterware 管理的组件都可以称为a CRS resource. A CRS resource 可以是 a database, an instance, a service, a listener, a VIP address, or an application process。

Oracle Clusterware 可管理的 CRS resources 基于资源配置信息 ，该配置信息存储在 Oracle Cluster Registry (OCR).

可以使用 SRVCTL 命令管理任何Oracle-defined的 CRS resources

这些资源自动started when Oracle Clusterware starts the node and automatically restarted if they fail.

三、Overview of Oracle RAC Architecture and Processing 

1、clusterware storage solutions

An Oracle RAC database is a shared everything database. All data files, control files, SPFILEs,and redo log files in Oracle RAC environments must reside on cluster-aware shared disks, so that all of the cluster database instances can access these storage component。

（1）ASM

（2）OCFS or OCFS2

（3）NFS

2、services and vip address

Oracle RAC database instances should be accessed through the Single Client Access Name (SCAN) for the cluster. Incoming connections are load balanced across the active instances providing the requested service through the three SCAN listeners. With SCAN, you do not have to change the client connection even if the configuration of the cluster changes (nodes added or removed).

The interconnect network is a private network that connects all of the servers in the cluster

If a node fails, then the node's VIP address fails over to another node

3、About Oracle RAC Software Components 

 An Oracle RAC database has the same processes and memory structures as a noncluster Oracle database and additional processes and memory structures（cache fusion） that are specific to Oracle RAC.  

The SGA size requirements for Oracle RAC are greater than the SGA requirements for noncluster Oracle databases due to Cache Fusion.

To ensure that each Oracle RAC database instance obtains the block that it requires to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances, which effectively increases the size of the SGA for an Oracle RAC instance.

After one instance caches data, any other instance within the same cluster database can acquire a block image from another instance in the same database faster than by reading the block from disk. Therefore, Cache Fusion moves current blocks between instances rather than re-reading the blocks from disk

4、About Oracle RAC Background Processes

四、Overview of Automatic Workload Management 

五、Overview of installing oracle rac

六、Overview of managing oracle rac environments