5.2.3.4 Using the limit Attribute

The limit attribute specifies the maximum flash I/O utilization limit as a percentage of the available resources.

You can use the limit attribute to restrict the flash I/O utilization for an entity in the interdatabase plan or the cluster plan. This attribute ensures that the specified entity never utilizes flash I/O resources beyond the specified limit. The attribute applies only to I/O on flash devices, which includes flash-based grid disks and Exadata Smart Flash Cache.

For example, if a production and test database are sharing Oracle Exadata Storage Server resources, then you could set a maximum flash utilization limit for the test database in the interdatabase plan as follows:

ALTER IORMPLAN dbplan=((name=prod),               -
                       (name=test, limit=20),     -
                       (name=DEFAULT, limit=10))

If maximum utilization limits are specified, then excess capacity might not be used. As a result, it is possible for flash devices to run below full capacity when maximum utilization limits are specified.

Note:

Specifying low limit values can have a significant performance impact and is generally not advisable.

Resource management using limits is ideal for pay-for-performance use cases but should not be used to implement fairness. Instead, use the share attribute to ensure equitable distribution of I/O resources.