Components of Real application Cluster

Oracle Real Application Cluster 10g provides you with an integrated software solution that addresses cluster management, event management, application management, connection management, storage management, load balancing and availability. These capabilities are addressed while hiding the complexity through simple-to-use management tools and automation.

Cluster platforms depend on the cluster management program to track the cluster node status. Basically there are two types of cluster managers, first one is oracle supplied and second one is vendor supplied.

In Oracle 10g , oracle provided clusterware can be used independently or on top of the vendor provided cluster software.

Cluster Ready Service’ (CRS) is Oracle provided portable clusterware, which is portable and works on all the platforms to implement RAC database solution.

RAC Software Principles

Addition to the background processes found in single instance database, You see few additional background processes associated with RAC instance. These processes are primarily used to maintain database coherency among each instance. They manage what is called the global resources:-

• LMON:- Global Enqueue Service Monitor
• LMD 0:- Global Enqueue Service Daemon
• LMSx :- Global Cache Service Processes
• LCK 0 :- Lock Process
• DIAG :- Diagnosibility Process

The Oracle Clusterware Software Components

When Oracle Clusterware operates, several platform-specific processes or services will also be running on each node in the cluster to support Oracle Clusterware.

Oracle Clusterware Processes on UNIX-Based Systems

• crsd—Performs high availability recovery and management operations such as maintaining the OCR and managing application resources. This process runs as the root user, or by a user in the admin group on Mac OS X-based systems. This process restarts automatically upon failure



• evmd—Event manager daemon. This process also starts the racgevt process to manage FAN server callouts



• ocssd—This process runs as oracle user and manages cluster node membership. Any failure of this process results in cluster restart



• oprocd—Cluster Process monitor. This process only appears on platforms that do not use vendor clusterware with Oracle Clusterware