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In Oracle9i, the query optimizer used an I/O cost model
based on single block reads.
Switching consumer groups
The DRM can switch consumer groups dynamically. You might want to give a
particular consumer group a high allocation of CPU resources. But if a single
query from that group looks as if it will take up too many CPU resources and
affect the overall performance of the machine, the consumer group can be
switched to another group that has a smaller CPU allocation??”for example, a
consumer group designed for batch operations.
Database Resource Manager | 185
Limiting number of connections
The DRM can limit the number of connections for any particular consumer
group. If the limit on connections for a group has been reached and another
connection request comes in, the connection request is queued until an existing
connection is freed. By limiting the overall number of connections for a consumer
group, you can place some rough limits on the overall resources that particular
group might require.
In Oracle Database 11g, the database installs with a default DRM plan.


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