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

problems with optimization. The conflicts threshold tab allows you to control how aggressively
SA can enforce inconsistencies. See Figure 3-59.
Figure 3-59 Conflict statistics threshold setup
Summarizing what the Statistics Advisor can do:
► Automate the analysis of the statistics required for an SQL statement. Often a query can
have inefficient or unstable performance due to lack of statistics.
► Generate a report explaining why you need the recommended RUNSTATS
► Show the statistics conflict that you have in your catalog
► Submit the RUNSTATS using a stored procedure
► Automate the solution to many common SQL performance problems and solve SQL
performance problems quickly and easily.
3.15.4 Visual Explain and Statistics Advisor on MQTs
To illustrate, we show screens from Visual Explain and Statistics Advisor taken using one
query from the member DSNTEJ3M (from SDSNSAMP).
Table 3-13 Query using MQT table
Query MQT table
Note: Do not forget to set the Current Refresh Age Parameters = Any (from the Visual
Explain - Tune SQL Screen); otherwise, EXPLAIN does not show you the MQTs you are
using.
We put the whole query on Table 3-13 in case you want to do the same tests we did.
SELECT R1.DAY, R1.MONTH, R1.YEAR, R10.CITYID, R7.DIVISIONID, SUM(R15.QUANTITY) SUMQTY,
SUM(R15.COST) SUMCOST, SUM(R15.AMOUNT) SUMAMT, SUM(R15.AMOUNT) - SUM(R15.COST) GPROFIT
FROM DSN8810.TIME R1, DSN8810.PRODUCT R5, DSN8810.LOCATION R10, DSN8810.PCATEGORY R6,
DSN8810.SALESFACT R15, DSN8810.PFAMILY R7
WHERE R1.TIMEID = R15.TIMEID AND R5.PRODUCTID = R15.PRODUCTID
AND R5.CATEGORYID = R6.CATEGORYID AND R6.FAMILYID = R7.FAMILYID
AND R10.STOREID = R15.STOREID AND R1.YEAR >= 2000
GROUP BY R1.DAY, R1.MONTH, R1.YEAR, R10.CITYID, R7.DIVISIONID;
Chapter 3. SQL performance 123