2.1.4 Prioritize Critical Large Writes in Flash Cache

Exadata optimizes the performance of large analytical queries and data-loading operations by absorbing large writes in Exadata Smart Flash Cache. Exadata limits the amount of flash cache space allocated to this purpose so that large writes cannot flood the cache and impact other workloads. However, Exadata historically could not distinguish between different categories of large writes, and all large writes had to share the same flash cache resources regardless of their relative performance implications.

Oracle Exadata System Software release 25.2.0 introduces algorithms to prioritize large writes in Exadata Smart Flash Cache. Under this arrangement, priority is granted to large writes associated with specific operations that consistently deliver the greatest performance benefits. The priority list primarily includes large writes associated with temporary (TEMP) segments and flashback logging.

Prioritization of large writes in Exadata Smart Flash Cache occurs only when flash cache utilization exceeds 50%, either in terms of overall flash cache space usage or in terms of the flash cache space allocated to the associated Exadata I/O Resource Management (IORM) group. When utilization is below the 50% threshold, all large writes have the same opportunity to use the cache as before. While utilization exceeds the 50% threshold, only prioritized large writes are allowed to use the cache.