The first is several terms that need to be understood: a cluster refers to the physical connection of multiple computers. RAC is short for Oracle Real Application cluster. Official Chinese documents are generally translated as "real application cluster". It generally consists of two or more homogeneous computers and shared storage devices, powerful processing capabilities! Why do we need RAC? If we add a CPU to the server and add Ram to the server, and other actions are vertical scaling, then performing RAC on multiple computers is a horizontal scaling! High Availability is its main feature! As long as one machine in the cluster does not fail, it can ensure normal use of users! Of course, if there is a major disaster, you should use the Oracle9i data guard failover solution! In addition, scalability is also its main feature! When the funds are limited, you do not need to buy equipment with high configurations for the moment. You only need to purchase the equipment that can meet the current needs. When the business volume increases, consider buying devices with the same configuration (the price should be low at this time )! How does RAC work? In the RAC environment, one instance runs on each computer, and each instance loads and opens the same database! All instances are peer-to-peer. The cache is shared to avoid repeated changes! A new term SERVICE_NAME for Oracle9i is prepared for RAC. All instances have the same service name! Applications only need to connect to this service. This service will automatically connect them to an instance! Transparent to these applications! (* Oracle also has an oracle_sid. Each instance has an independent Sid )! In general, we can use RAID technology to protect Disk redundancy technology to protect the network Oracle RAC to protect the database
