Oracle RAC Cache Fusion Deep Dive: How Blocks Travel Between Instances
Cache Fusion is the technology that allows Oracle RAC nodes to share a single consistent view of the database buffer cache across all instances. Without it, every cross-instance read or write would require a disk I/O. With it, dirty blocks travel directly from one instance’s buffer cache to another across the private interconnect. Understanding how this works is the foundation for diagnosing RAC-specific performance problems. The Problem Cache Fusion Solves In a traditional single-instance Oracle database, the buffer cache is authoritative. When an instance needs a block, it either finds it in cache or reads it from disk. In RAC, multiple instances have their own buffer caches, but they share the same datafiles. Without coordination, Instance A and Instance B could each have different versions of the same block in cache — a consistency nightmare. ...