Oracle8i SQL Reference Release 2 (8.1.6) A76989-01 |
|
SQL Statements (continued), 2 of 17
storage_clause: See "storage_clause".
To redefine storage and parallelism characteristics of a cluster.
For information on creating a cluster, see "CREATE CLUSTER".
To remove tables from a cluster, see "DROP CLUSTER" and "DROP TABLE".
The cluster must be in your own schema or you must have ALTER
ANY
CLUSTER
system privilege.
schema |
is the schema containing the cluster. If you omit schema, Oracle assumes the cluster is in your own schema. |
|
cluster |
is the name of the cluster to be altered. |
|
physical_attributes_clause |
changes the values of the |
|
|
storage_clause |
changes the storage characteristics for the cluster. See the "storage_clause".
Restriction: You cannot change the values of the storage parameters |
|
determines how many cluster keys will be stored in data blocks allocated to the cluster. For a description of the
Restriction: You can change the |
|
allocate_extent_clause |
explicitly allocates a new extent for the cluster. Restriction: You can allocate a new extent only for an indexed cluster, not for a hash cluster. |
|
|
|
specifies the size of the extent in bytes. Use K or M to specify the extent size in kilobytes or megabytes.
When you explicitly allocate an extent with this clause, Oracle does not evaluate the cluster's storage parameters and determine a new size for the next extent to be allocated (as it does when you create a table). Therefore, specify |
|
|
specifies one of the datafiles in the cluster's tablespace to contain the new extent. If you omit this parameter, Oracle chooses the datafile. |
|
|
makes the new extent available to the specified instance. An instance is identified by the value of its initialization parameter |
deallocate_unused_clause |
explicitly deallocates unused space at the end of the cluster and makes the freed space available for other segments. Only unused space above the high water mark can be freed. |
|
|
|
specifies the number of bytes above the high water mark that the cluster will have after deallocation. If the number of remaining extents is less than |
|
For a more complete description of this clause, see "ALTER TABLE". |
|
parallel_clause |
changes the default degree of parallelism for queries and DML on the cluster. See Also: The Notes to the parallel_clause of "CREATE TABLE". |
|
|
|
specifies serial execution. This is the default. |
|
|
causes Oracle to select a degree of parallelism equal to the number of CPUs available on all participating instances times the value of the |
|
|
specifies the degree of parallelism, which is the number of parallel threads used in the parallel operation. Each parallel thread may use one or two parallel execution processes. Normally Oracle calculates the optimum degree of parallelism, so it is not necessary for you to specify integer. |
|
Restriction: If the tables in cluster contain any columns of LOB or user-defined object type, this statement as well as subsequent |
The following statement alters the CUSTOMER
cluster in the schema SCOTT
:
ALTER CLUSTER scott.customer SIZE 512 STORAGE (MAXEXTENTS 25);
Oracle allocates 512 bytes for each cluster key value. Assuming a data block size of 2 kilobytes, future data blocks within this cluster contain 4 cluster keys per data block, or 2 kilobytes divided by 512 bytes. The cluster can have a maximum of 25 extents.
The following statement deallocates unused space from the CUSTOMER
cluster, keeping 30 kilobytes of unused space for future use:
ALTER CLUSTER scott.customer DEALLOCATE UNUSED KEEP 30 K;
|
Copyright © 1999 Oracle Corporation. All Rights Reserved. |
|