DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

Example
In DB2 V8 SQL/XML publishing functions become available. Storing and shredding or
decomposing XML documents is still only provided in the XML extender. As an example we
present in Figure 7-19 the results of shredding an XML document as a function of the
document size with the XML extender.
Time in second
Figure 7-19 XML extender decomposition
Decomposing an XML document into 3 tables of 20 columns on a z990 system takes 10 to 40
seconds for document sizes ranging from 1 to 6 MB.
7.5.2 XML publishing functions
DB2 V8 now provides seven new built-in XML publishing functions to help with XML
document composition from DB2 data.
Description
The XML publishing functions are built-in DB2 functions. They run inside the DB2 address
spaces, unlike external User Defined Functions (UDFs), for example from the XML extender,
that run in a WLM managed address space outside of DB2. The fact that the XML publishing
functions are built into the DB2 engine gives them better performance.
XML data type
An XML data type is an internal representation of XML, and can be used only as input to
built-in functions that accept this data type as input. XML is a transient data type that cannot
be stored in the database or returned to an application. Transient means that this data type
only exists during query processing. There is no persistent data of this type and it is not an
external data type that can be declared in application programs. In other words, the XML data
type cannot be stored in a database or returned to an application.
Valid values for the XML data type include the following:
► An element
► A forest of elements
► The textual content of an element
► An empty XML value
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XML Extender - Decomposition
Decomposition by doc size
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Doc size (MBytes)