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

in ms = 1 and the CPU cost is 16 service units. We save 1 millisecond, or 16 SUs on
accessing a very small catalog.
Figure 3-48 Consistency query - 31 New
3.15.3 Statistics Advisor
Statistics Advisor is a new function from the Web, available with Visual Explain. Its main
purpose is to help you identify the RUNSTATS executions that help your SQL. Sometimes it is
not simple at all to understand which statistics can help your queries. The Statistics Advisor
builds the RUNSTATS statements for the correct set of statistics, gives you consistent and
accurate information, and you just need to run the RUNSTATS and perform some tests, and
the problem is solved. You can continue to run the Statistics Advisor until it no longer provides
suggestions.
The Statistics Advisor (SA) analyzes the predicates, column (groups) used as predicates,
type of predicates, performs statistical analysis, checks missing statistics (default), conflicting
statistics, missing appropriate correlations, and skew statistics. Based on all of that, the
Statistics Advisor gives you suggestions on the RUNSTATS to execute. Furthermore, it gives
you an explanation and a conflict report.
We use the following simple SQL statement against the EMP table of the DB2 V8 sample
database:
SELECT * FROM DSN8810.EMP WHERE HIREDATE < '2004-12-31' AND SALARY < 25000 AND SEX = 'M';
We start SA from the main panel, shown in Figure 3-49, where we enter the statement to be
analyzed, explained, or run.
116 DB2 UDB for z/OS Version 8 Performance Topics