Clusters (Oracle)

A cluster is a schema object that contains data from one or more tables, which have one or more columns in common. Oracle Database stores together all the rows from all the tables that share the same cluster key.

PowerDesigner models clusters as extended objects with a stereotype of <<Cluster>>.

Note:

Clusters in Oracle v10gR2 and earlier are modeled as indexes with the Cluster check box selected. To upgrade such clusters to v11 or higher, you must generate a new PDM with the appropriate DBMS target from your original model. Simply changing the target DBMS will result in the loss of any existing clusters

Creating a Cluster

You can create a cluster in any of the following ways:

  • Select Model > Clusters to access the List of Clusters, and click the Add a Row tool

  • Right-click the model (or a package) in the Browser, and select New > Cluster

Cluster Properties

You can modify an object's properties from its property sheet. To open a cluster property sheet, double-click its Browser in the Clusters folder.

The following extended attributes are available on the General tab:

Name

Description

Owner

Specifies the owner of the cluster

In addition, the following tabs are available:

  • Columns – lists the columns associated with the cluster. You can can define the following extended attributes for cluster columns:

    Name

    Description

    Data type

    Specifies the data type for the cluster index.

    Scripting name: Datatype

    Length

    Specifies the length for the cluster index.

    Scripting name: DatatypeLength

    Precision

    Specifies the precision for the cluster index.

    Scripting name: DatatypePrec

    Sort

    This clause instructs Oracle Database to sort the rows of the cluster on this column before applying the hash function.

    Scripting name: RowSort
  • Indexes – lists the indexes defined for the cluster. You can can define the following extended attributes for cluster columns:

    Name

    Description

    Owner

    Specifies the owner of the cluster index

    Scripting name: Owner

    Unique

    Specifies whether the cluster index is unique.

    Scripting name: Unique

    Bitmap

    Specifies if the index is to be created with a bitmap for each distinct key, rather than indexing each row separately.

    Scripting name: Bitmap

    Sort

    By default, Oracle Database sorts indexes in ascending order when it creates the index. You can specify NOSORT to indicate to the database that the rows are already stored in the database in ascending order, so that Oracle Database does not have to sort the rows when creating the index.

    Scripting name: Sort
Parent topic: Oracle