Oracle DBA

  Cache Fusion Explained Simply (Oracle RAC) In Oracle Real Application Clusters (RAC), multiple database instances run on different servers (nodes) but access the  same database  stored on shared storage (ASM or shared disk). This architecture provides  high availability, scalability, and load balancing . But this raises a big question: If multiple instances are accessing the same data blocks, how does Oracle maintain consistency and performance? The answer is  Cache Fusion . Cache Fusion is one of the  core technologies  that makes Oracle RAC possible and efficient. In this blog, we’ll explain Cache Fusion in  simple language , step by step, with examples. What Is Cache Fusion? Cache Fusion  is a mechanism in Oracle RAC that allows  data blocks to be transferred directly between the memory (buffer cache) of different RAC instances over a high-speed interconnect , instead of writing and reading blocks from disk. In short: Data blocks mo...

  In an Oracle RAC (Real Application Clusters) environment,  node failure is not an exception it’s an expected scenario . RAC is designed for  high availability , meaning the database should continue running even if one node goes down. This blog explains  step-by-step what actually happens when one node goes down , from the moment of failure to full stabilization, in  simple and practical DBA language . What Does “One Node Goes Down” Mean? A node can go down due to several reasons: Server crash or power failure OS hang or kernel panic Network failure Manual shutdown or reboot Hardware issues (CPU, RAM, disk) In RAC terms, this means: One  instance + its local services  are no longer available But  the database itself is NOT down . Immediate Detection by Oracle Clusterware Oracle Clusterware continuously monitors all nodes using: Voting disks Private interconnect What happens first? Surviving nodes  stop receiving heartbeat  from the fail...