What Is Exafusion ?

Exafusion allows database processes to read and send Oracle Real Applications Cluster (Oracle RAC) messages directly over the Infiniband network bypassing the overhead of entering the OS kernel, and running the normal networking software stack.

  • Lower latency
  • Improve response time
  • Higher throughput direct to wire block transfers between Oracle Real Application Clusters (Oracle RAC) instances
  • Reduced CPU utilization and better scale-out performance
  • Exafusion is especially useful for OLTP applications because per message overhead is particularly apparent in small OLTP messages. It helps small messages by bypassing OS network layer overhead. 

  • EXAFUSION_ENABLED parameter is used to enable or disable the Exafusion accelerate cache fusion protocol feature, which is available on the Linux operating system of Oracle Exadata Database Machine only.
  • Exafusion is disabled by default.
  • To enable Exafusion, set the EXAFUSION_ENABLED initialization parameter to 1. To disable Exafusion, set the EXAFUSION_ENABLED initialization parameter to 0.
  • This parameter cannot be set dynamically. It must be set before instance startup.

Prerequisites and Limitations
  • Oracle Storage Server Software release or later is required.
  • Mellanox ConnectX-2 and ConnectX-3 Host Channel Adapters (HCAs) are required.
  • Oracle Unbreakable Enterprise Kernel 2 Quarterly Update 5 (UEK2QU5) kernels (2.6.39-400.2nn) or later are required.
  • The Exafusion feature does not support mixed mode operation on an Oracle RAC cluster. Either all the instances in an Oracle RAC cluster must have the feature enabled or none.
  • Rolling upgrades of a non-Exafusion enabled Oracle RAC cluster to Exafusion are not supported.
  • Exafusion is available only on the Linux operating system of Oracle Exadata Database Machine
  • It is not supported on any non-engineered system or SPARC Super Cluster (SSC). If you set the EXAFUSION_ENABLED parameter on a non-supported platform, then the instance will be prevented from starting up, and an ORA-00439: The specified feature is not enabled: string error message is generated.
  • This initialization parameter is available starting with Oracle Database 12c Release 1 ( Bundle Patch 11 (BP11).
 Source: https://docs.oracle.com

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