Oracle 11gR2 rac 的各项服务说明

The Oracle Clusterware Stack

Oracle Clusterware consists of two separate stacks: an upper stack anchored by the Cluster Ready Services (CRS) daemon (crsd) and a lower stack anchored by the Oracle High Availability Services daemon (ohasd). These two stacks have several processes that facilitate cluster operations. The following sections describe these stacks in more detail:

oracle 集群包含两个技术栈：上层栈由CRS服务控制，下层栈由OHAS控制。这两个栈分别有几个processes来完成集群服务。下面分别介绍之。

The Cluster Ready Services Stack

The list in this section describes the processes that comprise CRS. The list includes components that are processes on Linux and UNIX operating systems, or services on Windows.

• Cluster Ready Services (CRS): The primary program for managing high availability operations in a cluster.

  The CRS daemon (crsd) manages cluster resources based on the configuration information that is stored in OCR for each resource. This includes start, stop, monitor, and failover operations. The crsd process generates events when the status of a resource changes. When you have Oracle RAC installed, the crsd process monitors the Oracle database instance, listener, and so on, and automatically restarts these components when a failure occurs.（集群就绪服务管理集群资源，这些资源是存储在ocr里的配置信息。包括对这些资源启停，监控等操作。当资源的状态改变的时候，crsd进程生产事件。）

• Cluster Synchronization Services (CSS): Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members when a node joins or leaves the cluster. If you are using certified third-party clusterware, then CSS processes interface with your clusterware to manage node membership information.

  The cssdagent process monitors the cluster and provides I/O fencing. This service formerly was provided by Oracle Process Monitor Daemon (oprocd), also known as OraFenceService on Windows. A cssdagent failure may result in Oracle Clusterware restarting the node.（cssdagent进程监控集群并且提供IO隔离。crss服务主要是提供集群同步，检查节点数量，增加减少节点）

• Oracle ASM: Provides disk management for Oracle Clusterware and Oracle Database.(提供集群和数据库的磁盘管理服务)

• Cluster Time Synchronization Service (CTSS): Provides time management in a cluster for Oracle Clusterware.（CTSS服务是一个可选项，通过网络时间协定服务器为集群提供时间同步，这个时间同步对RAC很重要。它可以运行在两种模式下：观望或者活动。当NTP被激活的时候，它运行在观察模式，若没有启动NTP，它将根据主节点同步所有节点的时间。）

• Event Management (EVM): A background process that publishes events that Oracle Clusterware creates.（发布集群产生的事件的进程——EVM负责发布Grid Infrastructure创建的事件）

• Oracle Notification Service (ONS): A publish and subscribe service for communicating Fast Application Notification (FAN) events.（负责通过快速应用框架发布事件的主要后台进程。）

• Oracle Agent (oraagent): Extends clusterware to support Oracle-specific requirements and complex resources. This process runs server callout scripts when FAN events occur. This process was known as RACG in Oracle Clusterware 11g release 1 (11.1).

• Oracle Root Agent (orarootagent): A specialized oraagent process that helps crsd manage resources owned by root, such as the network, and the Grid virtual IP address.

The Cluster Synchronization Service (CSS), Event Management (EVM), and Oracle Notification Services (ONS) components communicate with other cluster component layers on other nodes in the same cluster database environment. These components are also the main communication links between Oracle Database, applications, and the Oracle Clusterware high availability components. In addition, these background processes monitor and manage database operations.

The Oracle High Availability Services Stack

This section describes the processes that comprise the Oracle High Availability Services stack. The list includes components that are processes on Linux and UNIX operating systems, or services on Windows.

• Cluster Logger Service (ologgerd): Receives information from all the nodes in the cluster and persists in a CHM repository-based database. This service runs on only two nodes in a cluster.

• System Monitor Service (osysmond): The monitoring and operating system metric collection service that sends the data to the cluster logger service. This service runs on every node in a cluster.

• Grid Plug and Play (GPNPD): Provides access to the Grid Plug and Play profile, and coordinates updates to the profile among the nodes of the cluster to ensure that all of the nodes have the most recent profile.

• Grid Interprocess Communication (GIPC): A support daemon that enables Redundant Interconnect Usage.

• Multicast Domain Name Service (mDNS): Used by Grid Plug and Play to locate profiles in the cluster, as well as by GNS to perform name resolution. The mDNS process is a background process on Linux and UNIX and on Windows.

• Oracle Grid Naming Service (GNS): Handles requests sent by external DNS servers, performing name resolution for names defined by the cluster.

Table 1-1 lists the processes and services associated with Oracle Clusterware components. In Table 1-1, if a UNIX or a Linux system process has an (r) beside it, then the process runs as the root user.