Explanation
On an Exadata DB system, all databases share dedicated storage servers which include flash storage. By default, the databases are given equal priority with respect to these resources. The Exadata storage management software uses a first come, first served approach for query processing. If a database executes a major query that overloads I/O resources, overall system performance can be slowed down.
The I/O Resource Management (IORM) allows you to assign priorities to your databases to ensure critical queries are processed first when workloads exceed their resource allocations. You assign priorities by creating directives that specify the number of shares for each database. The number of shares corresponds to a percentage of resources given to that database when I/O resources are stressed.
Directives work together with an overall optimization objective you set for managing the resources. The following objectives are available:
1) Auto - Recommended. IORM determines the optimization objective and continuously and dynamically determines the optimal settings, based on the workloads observed, and resource plans enabled.
2) Balanced - For critical OLTP and DSS workloads. This setting balances low disk latency and high throughput. This setting limits disk utilization of large I/Os to a lesser extent than low latency to achieve a balance between good latency and good throughput.
3) High throughput - For critical DSS workloads that require high throughput.
4) Low latency - For critical OLTP workloads. This setting provides the lowest possible latency by significantly limiting disk utilization.