DPFXMLMOVEMENT requests

The DPFXMLMOVEMENT general request element can be used in partitioned database environments to override the optimizer's decision to choose a plan in which either a column of type XML is moved or only a reference to that column is moved between database partitions. It is defined by the complex type dpfXMLMovementType.

<xs:complexType name="dpfXMLMovementType">
   <xs:attribute name="VALUE" use="required">
      <xs:simpleType>
         <xs:restriction base="xs:string"
            <xs:enumeration value="REFERENCE"/>
            <xs:enumeration value="COMBINATION"/>
         </xs:restriction>
      </xs:simpleType>
   </xs:attribute>
</xs:complexType>

Description

In partitioned database environments, data must sometimes be moved between database partitions during statement execution. In the case of XML columns, the optimizer can choose to move the actual documents that are contained in those columns or merely a reference to the source documents on the original database partitions.

The DPFXMLMOVEMENT general request element has a required VALUE attribute with the following possible values: REFERENCE or COMBINATION. If a row that contains an XML column needs to be moved from one database partition to another:

REFERENCE specifies that references to the XML documents are to be moved through the table queue (TQ) operator. The documents themselves remain on the source database partition.
COMBINATION specifies that some XML documents are moved, and that only references to the remaining XML documents are moved through the TQ operator.

The decision of whether the documents or merely references to those documents are moved depends on the conditions that prevail when the query runs. If the DPFXMLMOVEMENT general request element has not been specified, the optimizer makes cost-based decisions that are intended to maximize performance.