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Prior to Oracle9i, if you wanted to cluster multiple database instances together to access the same data, you would use a product called Oracle Parellel Server (OPS). Late in Oracle8i, the concept of Cache Fusion was introduced for OPS. Cache Fusion lets Oracle instances in the cluster send data back and forth to other instances without having to write the data to disk first. Having to write data to disk first was known as "disk pinging" and slowed down application performance. When Oracle9i was introduced, Oracle Corp renamed OPS to Real Application Clusters (RAC). This was due, in part, to Cache Fusion along with other improvements to the cluster software. Oracle10g still
uses RAC in their documentation. But Oracle 10g's grid strategy relies heavily on RAC for its implementation. Oracle is not calling the software "grid." At this time, grid is more of a concept that uses Oracle software for its implementation.
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