Cache fusion is a mechanism used in Oracle Real Application Clusters (RAC) to enable multiple instances to access the same data in a shared cache. It is a key part of the RAC architecture and allows nodes in a cluster to access and modify data in a coordinated and consistent manner.
In a RAC system, each node has its own private cache in which it stores data that it has recently accessed from the database. When a node needs to access data that is not in its private cache, it can request the data from another node that has the data in its cache. This is known as a cache fusion operation.
Cache fusion is a complex process that involves coordinating the transfer of data blocks between the different nodes in the cluster. It uses a variety of mechanisms, such as locks and versioning, to ensure that the data being accessed is consistent and up-to-date. It also ensures that multiple nodes do not attempt to modify the same data block at the same time, which could cause data corruption.
Overall, cache fusion is an essential part of the RAC architecture and is key to the ability of RAC systems to provide high levels of performance, scalability, and availability.
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