An Oracle RAC database has the same processes and memory structures as a single-instance Oracle database as well as additional process and memory structures that are specific to Oracle RAC.
The list of Oracle RAC processes are:
1)LMS—Global Cache Service Process
2)LMD—Global Enqueue Service Daemon
3)LMON—Global Enqueue Service Monitor
4)LCK0—Instance Enqueue Process
After one instance caches data, any other instance within the same cluster database can acquire a block image from another instance in the same database faster than by reading the block from disk. This is called cache fusion, any instance need data that is cached by other instance, is passed to it by using private interconnect.
The Global Cache Service(GCS) and Global Enqueue Service(GES) maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). Oracle RAC processes and the GRD collaborate to enable Cache Fusion.
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