|Lesson 4|| Sizing a cluster |
|Objective|| Properly size a cluster.|
Properly Sizing an Oracle Cluster
In a non-clustered table, the size of the data to be contained in the table is not a great concern.
A DBA always must be sure to have enough disk space to store data, but management of the underlying storage is handled by your Oracle database. When you use a cluster, however, you are explicitly linking data, by value, with the way it is stored on disk. Because of this, you must specify a size for the data associated with a particular value of the cluster key.
How do you size a cluster?
The CREATE CLUSTER command has a required SIZE parameter.
You can specify this size either in K(ilobytes) or M(egabytes). When you create a cluster, each time you add a value for the cluster key, Oracle allocates the number of data blocks required by the value in the SIZE clause.
The size specified in the CREATE CLUSTER should be large enough to store all of the data for all of the rows associated with the cluster value and the cluster value itself.
Improperly size your cluster?
If you size your cluster too small, the data for the cluster value will extend beyond the pre-allocated space, and the additional chaining will reduce the overall performance advantages of the cluster.
If you specify too large a size for your cluster, you will end up wasting disk space, which can also contribute to reduced disk and database performance. The next lesson shows how to create a cluster index.
Sizing Cluster - Exercise