Oracle RAC Clusterware Technology stack 19c

The Oracle Clusterware Technology Stack (19c)

Oracle Clusterware consists of two separate technology stacks: an upper technology stack anchored by the Cluster Ready Services (CRS) daemon (CRSD) and a lower technology stack anchored by the Oracle High Availability Services daemon (OHASD).

These two technology stacks have several processes that facilitate cluster operations. The following sections describe these technology stacks in more detail.

The Cluster Ready Services Technology Stack

The Cluster Ready Services (CRS) technology stack leverages several processes to manage various services.

The following list describes these processes:

• Cluster Ready Services (CRS): The primary program for managing high availability operations in a cluster.
• The 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.
• 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.
• Oracle ASM: Provides disk management for Oracle Clusterware and Oracle Database.
• Cluster Time Synchronization Service (CTSS): Provides time management in a cluster for Oracle Clusterware.
• Event Management (EVM): A background process that publishes events that Oracle Clusterware creates.
• Grid Naming Service (GNS): Handles requests sent by external DNS servers, performing name resolution for names defined by the cluster.
• 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 Notification Service (ONS): A publish and subscribe service for communicating Fast Application Notification (FAN) events.
• Oracle Root Agent(orarootagent): A specialized oraagent process that helps the CRSD manage resources owned by root, such as the network, and the Grid virtual IP address.

The Oracle High Availability Services Technology Stack

The Oracle High Availability Services technology stack uses several processes to provide Oracle Clusterware high availability.

The following list describes the processes in the Oracle High Availability Services technology stack:

• appagent: Protects any resources of the application resource type used in previous versions of Oracle Clusterware.
• Cluster Logger Service (ologgerd): Receives information from all the nodes in the cluster and persists in an Oracle Grid Infrastructure Management Repository-based database. This service runs on only two nodes in a cluster.
• Grid Interprocess Communication (GIPC): A support daemon that enables Redundant Interconnect Usage.
• 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.
• Multicast Domain Name Service (mDNS): Used by Grid Plug and Play to locate profiles in the cluster, and by GNS to perform name resolution. The mDNS process is a background process on Linux and UNIX and on Windows.
• Oracle Agent (oraagent): Extends clusterware to support Oracle-specific requirements and complex resources. This process manages daemons that run as the Oracle Clusterware owner, like the GIPC, GPNPD daemons.
• Oracle Root Agent (orarootagent): A specialized oraagent process that helps the CRSD manage resources owned by root, such as the Cluster Health Monitor (CHM).
• scriptagent: Protects resources of resource types other than application when using shell or batch scripts to protect an application.
• 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.