|Oracle® Database SQL Language Reference
12c Release 1 (12.1)
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CLUSTER statement to redefine storage and parallelism characteristics of a cluster.
Note:You cannot use this statement to change the number or the name of columns in the cluster key, and you cannot change the tablespace in which the cluster is stored.
The cluster must be in your own schema or you must have the
CLUSTER system privilege.
Specify the schema containing the cluster. If you omit
schema, then Oracle Database assumes the cluster is in your own schema.
Specify the name of the cluster to be altered.
Use this clause to change the values of the
INITRANS parameters of the cluster.
STORAGE clause to change the storage characteristics of the cluster.
SIZE clause to specify the number of cluster keys that will be stored in data blocks allocated to the cluster.
allocate_extent_clause to explicitly allocate a new extent for the cluster.
When you explicitly allocate an extent with this clause, Oracle Database does not evaluate the storage parameters of the cluster and determine a new size for the next extent to be allocated (as it does when you create a table). Therefore, specify
SIZE if you do not want Oracle Database to use a default value.
See Also:allocate_extent_clause for a full description of this clause and "Deallocating Unused Space: Example"
deallocate_unused_clause to explicitly deallocate unused space at the end of the cluster and make the freed space available for other segments.
See Also:deallocate_unused_clause for a full description of this clause
This clause has the same behavior in
See Also:"CACHE | NOCACHE" for information on this clause.
parallel_clause to change the default degree of parallelism for queries and
DML on the cluster.
Restriction on Parallelized Clusters If the tables in
cluster contain any columns of LOB or user-defined object type, then this statement as well as subsequent
DELETE operations on
cluster are executed serially without notification.
See Also:parallel_clause in the documentation on
TABLEfor complete information on this clause
The following examples modify the clusters that were created in the
ALTER CLUSTER personnel SIZE 1024 CACHE;
Oracle Database allocates 1024 bytes for each cluster key value and enables the cache attribute. Assuming a data block size of 2 kilobytes, future data blocks within this cluster contain 2 cluster keys in each data block, or 2 kilobytes divided by 1024 bytes.
ALTER CLUSTER language DEALLOCATE UNUSED KEEP 30 K;