Service descriptions for Oracle 11gR2 RAC

After installation, some background processes are generated to ensure that the cluster is working properly and that it can communicate with the outside. The requirements for some of these ordered Linux platforms need to be started with root user privileges. For example, changes to the network configuration require higher permissions. Other background processes will run with the permissions of the system user on which the grid software resides. The following table describes some of the main background processes

Background process	Description
Oracle High-Availability Service (Ohas)	Ohas is the first grid infrastructure component that opens after the server starts. It is configured to open with Init (1) and negative Responsible for generating the agent process.
Oracle Agent	The Grid infrastructure uses two Oracle agent processes. The first one, to summarize, is responsible for opening up some of the required access The resources for OCR and voting files. It is created by Ohas. The second agent process is created by CRSD and is responsible for opening all resources that do not require root access. This process takes The Grid infrastructure the permissions of the owning user and is responsible for RACG the work done in RAC11.1.
Oracle Root Agent	Similar to the Oracle proxy process, there are two root agent processes created. The initial agent process was raised by Ohas and it Provides initialization for resources in a Linux system that require higher permissions. The main background processes created are CSSD and CRSD. Anti - Come on, CRSD will trigger another root agent. This agent will open the resources that require root, primary and network related
Cluster Readiness Service Process (CRSD)	Background main process of cluster software, using Oracle Cluster registration information to manage resources in the cluster
Cluster Synchronization Service Process (CSSD)	Managing the configuration and node members of a cluster
Oracle Process Monitoring (OPROCD)	OPROCD is responsible for I/O isolation in version 11.1. It was introduced in the 10.2.0.4 patch set for Linux systems. In this patch Previously, the kernel Hangcheck-timer modules to do similar tasks. Interestingly, OPROCD used to be used in non- Linux platform. Grid infrastructure replaces the OPROCD process with the cssdagent process.
Event Manager (EVM)	EVM is responsible for publishing the events created by grid infrastructure
Cluster time Synchronization Service (CTSS)	The CTSS service is an option to provide time synchronization for a cluster over a network Time protocol server, which synchronizes RAC is important. It can be run in two modes: watching or moving. When NTP is activated, it runs on the Observation mode, if NTP is not started, it will synchronize the time of all nodes according to the master node.
Oracle Warning Service (ONS)	The main background process responsible for publishing events through the Rapid application framework.

The Oracle clusterware Stack

Oracle Clusterware consists of the separate Stacks:an upper stack anchored by the Cluster ready Services (CRS) Daemon ( ) and a lower stack anchored by the Oracle high Availability Services Daemon ( ohasd ). These stacks has several processes that facilitate cluster operations. The following sections describe these stacks in more detail:

The Oracle cluster consists of two technology stacks: the upper stack is controlled by the CRS service and the lower stack is controlled by Ohas. The two stacks have several processes to complete the Cluster service. The following are described separately.

The Cluster ready Services Stack

The list in this section describes the processes that comprise CRS. The list includes components is 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 this 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, Listene R, and so on, and automatically restarts these is a failure occurs. (Cluster readiness Service manages cluster resources, which are configuration information stored in OCR.) This includes operations such as starting and stopping these resources, monitoring and so on. The CRSD process produces events when the state of the resource changes. )

• Cluster synchronization Services (CSS): Manages the Cluster configuration by controlling which nodes is members of the CL Uster and by notifying members when a node joins or leaves the cluster. If you is using certified Third-party clusterware, then CSS processes interface with your clusterware to manage node memb Ership information.

  The cssdagent process monitors the cluster and provides I/O fencing. This service formerly is provided by the Oracle Process Monitor Daemon ( oprocd ), also known as on OraFenceService Windows. A cssdagent failure may result in Oracle Clusterware restarting the node. (cssdagent process monitors the cluster and provides IO isolation. CRSs service is mainly to provide cluster synchronization, check the number of nodes, increase the reduction of nodes)

• Oracle Asm:provides Disk Management for Oracle Clusterware and Oracle Database. (Provides disk Management services for clusters and databases)

• Cluster Time Synchronization Service (CTSS): Provides time management in a Cluster for Oracle Clusterware. (CTSS service is an option to The Network Time Protocol server provides time synchronization for the cluster, which is important for RAC. It can be run in two modes: watching or moving. When NTP is activated, it runs in observation mode, and if NTP is not started, it synchronizes all nodes ' time based on the master node. ）

• Event Management (EVM): A background process, that publishes events, Oracle Clusterware creates. (Release of the event generated by the cluster--EVM responsible for publishing g RID Infrastructure event created)

• Oracle Notification Service (ONS): A Publish and subscribe service for communicating Fast application Notification (FAN) E Vents. (The main background process responsible for publishing events through the Quick Application framework.) ）

• 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 is known as RACG in Oracle clusterware oneG Release 1 (11.1).

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

The Cluster synchronization Service (CSS), Event Management (EVM), and Oracle Notification Services (ONS) components Commu Nicate with other cluster component layers on other nodes in the same cluster database environment. These components is also the main communication links between Oracle Database, applications, and the Oracle Clusterware H IgH 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 is 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 repositor y-based database. This service, runs on, is nodes in a cluster.

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

• Grid Plug and Play (GPNPD): Provides access to the Grid Plug and play profiles, and coordinates updates to the profile Amon G The nodes of the cluster to ensure, all of the nodes has the most recent profiles.

• 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 P Erform name resolution. The MDNS process is a background process on Linux and UNIX with on Windows.

• Oracle Grid naming Service (GNS): Handles requests sent by external DNS servers, performing name resolution for names Defi Ned 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 have an (r) beside it, then the process runs as the root user.

Ext.: http://blog.csdn.net/cymm_liu/article/details/21446605

Service descriptions for Oracle 11gR2 RAC