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

An auxiliary node includes any nodes that are neither data source nodes nor operator
nodes.
Both query nodes and query block nodes are classified as auxiliary nodes. Most of the nodes
have corresponding descriptors, which store detailed information about the data source,
query, or operation that is represented by the node. The Descriptor window lists all of the
attribute values for the data source, query, or operation that is represented by the node. From
the Descriptor window, you can also link to any related descriptors. For example, from the
descriptor for a table node, you can link to the descriptors for the indexes that are defined on
that table.
We use the consistency query 31, listed in Appendix 3-11, “Old consistency query 31” on
page 113 to show an example of the EXPLAIN.
Table 3-11 Old consistency query 31
The old Query 31
SELECT NAME
FROM SYSIBM.SYSPLAN PL
WHERE PLENTRIES = 0
AND NOT EXISTS
(SELECT * FROM SYSIBM.SYSDBRM WHERE PLNAME = PL.NAME);
This query with correlated subquery selects the names of plans that have PLENTRIES=0 and
have no DBRM pointing to the name of the plan. If you want more information about the
consistency query, take a look at 9.5, “Catalog consistency query DSNTESQ” on page 359.
There you find some measurements and more details about it.
Now let us analyze the Visual Explain from the Query 31. Figure 3-47 shows the EXPLAIN
and tells us that the cost of CPU is 2 milliseconds (in service units the cost is 32).
Chapter 3. SQL performance 113