Oracle Clusterware - OCSSd

OCSSd

Oracle Cluster Synchronization Services daemon (OCSSd) provides basic ‘group services’ support. Group Services is a distributed group membership system that allows the applications to coordinate activities to achieve a common result. As such, it provides synchronization services between nodes, access to the node membership information, as well as enabling basic cluster services, including cluster group services and cluster locking. It can also run without integration with vendor clusterware. Failure of OCSSd causes the machine to reboot to avoid a split-brain situation. This is also required in a single instance configuration if Automatic Storage Management (ASM) is used. ASM was a new feature in Oracle 10g. OCSSd runs as the "oracle" user.

The following functions are provided by the Oracle Cluster Synchronization Services daemon (OCSSd):

• ’Group Services’ uses vendor-provided clusterware group services when the latter is available, but is also capable of working independently if that is unavailable
• ‘Lock Services’ provides the basic cluster-wide serialization locking functions, and uses a FIFO mechanism to manage locking
• 'Node Services' uses OCR to store state data, and updates the information during reconfiguration. It also manages the OCR data, which is static otherwise.