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21.	What is cache fusion?
	In a RAC setup, each node has its own memory; however, they share physical datafiles. As we know that data blocks are read into memory for updates or query in a single instance database. Similarly, in a RAC set up, a node reads a block from datafile when the node needs it. However, in RAC setting, the required block may be already available in the memory of another node and it is faster to read block from the memory of another block than from a datafile. Therefore, RAC provides a mechanism to read block from memory of one node to the memory of another node. This mechanism is called cache fusion. Oracle uses high speed interconnect to communicate between nodes. GES monitors and the Instance Enqueue process manages the cache fusion.
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22.	List the background processes required for RAC?
	The background processes required for RAC are given as follows ACMS – Atomic Controlfile to Memory Service LMON – Global Enqueue Service Monitor LMD – Global Enqueue Service Daemon LMS – Global Cache Service Process LCK0 – Instance Enqueue Process RMSn – Oracle RAC Management Processes RSMN – Remote Slave Monitor
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23.	How is RAC different from non RAC clusters?
	A non RAC database has a single node while a RAC database has multiple (at least two) nodes. The nodes in a RAC set up share storage. RAC offers failover option while a non RAC database does not offer failover option because it is based on a single node
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24.	What is interconnect network?
	An interconnect network is a network between nodes of a cluster. It uses switches to ensure that only nodes can access this network. Generally, this is a high speed connection.
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