Oracle RAC main components… (quick self memo)

I always forget how to resolve those shortcuts and which one does what, especially CSS versus CRS :)

CSS – Cluster Synchronization Services – Component responsible for controlling which nodes are members of the clusters. When node joins or leaves the cluster, CSS notifies the other nodes of the change in configuration. If this process fails, then the cluster will be restarted. Under Linux, CSS is implemented by the ocssd daemon, which runs as the root user.

CRS – Cluster Ready Services – Manages resources (databases, instances, services, listeners, VIPs, application processes, GSD, ONS) Configuration is stored in OCR. When status of resource changes CRS emits an event. CRS will try to restart resource up to 5 times before giving up. Under Linux, CRS is implemented as the crsd process, which runs with root privileges. In the event of failure this process restarts automaticlly.

EVM - Event Manager – Implemented as the evmd daemon (also runs as root). Oracle Clusterware also communicates with the ONS, which is a publish & subsribe service that communicates FAN events to clients.

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