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Oracle Exadata Database Machine

Exafusion Direct-to-Wire Protocol

Overview

Exafusion Direct-to-Wire Protocol is a database optimization for Exadata that allows Oracle Real Application Cluster (RAC) Databases to send and recieve messages directly between instances circumventing the local operating system and network stack. Exafusion leads to response time improvements and greater database scalability by reducing the processing requirements of these inter-instance messages.

In an Oracle RAC envirnoment, each database instance caches data blocks in its System Global Area (SGA) to satisfy queries and transactions. If another instance in the cluster requires that block, it is passed between instances.

After one instance caches data, any other instance within the same cluster database can acquire a block image from another instance in the same database faster than by reading the block from disk. Cache Fusion moves current blocks between instances rather than re-reading the blocks from disk. When a consistent block is needed or a changed block is required on another instance, Cache Fusion transfers the block image directly between the affected instances. Oracle RAC uses the private interconnect for interinstance communication and block transfers (Source: Oracle RAC Admin Documentation)

Exafusion Direct-to-Wire Protocol is an optimization to the way Oracle RAC implements Cache Fusion on Exadata, enabling Oracle Database 12.1.0.2 (BP13) and higher to directly interface with the RDMA over Converged Ethernet (RoCE) network cards bypassing the Operating System kernel, and network software thereby improving performance for OLTP workloads significantly.