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

► V8 using MQT
0.92 sec. elapsed time and 0.11 sec. CPU time
The measurements show that the elapsed time was 49 times smaller (about 97%) and CPU
time 117 times smaller (about 99%) when we compare V7 DEGREE(1) with V8 using an
MQT.
Expression derivation
► Arithmetic expressions: (A+B)*C can be derived from B+A and C
► Column equivalence: If TI.C1=T2.C1, T2.C1 can be used for T1.C1
► Scalar functions: SUBSTR(A,3,5) can be derived from A
► Set functions: AVG(C) can be derived from SUM(C) and COUNT(*) if C NOT NULL
Figure 3-14 shows one example of expression derivation using an MQT.
Expression derivation
Query
Figure 3-14 Expression® derivation example
In the example the populated MQT673 is the result of joining three tables and two
aggregations:
SUM(COV.MCP),SUM(PLC.CAS)
The measured query selects
SUM(COV.MCP) + SUM(PLC.CAS)
This can be derived from the two aggregated columns from MQT.
The predicates
SELECT
CREATE TABLE MQT673 ( COUNT,SUM1,SUM2,CVT) AS(
SELECT
COUNT(DISTINCT PLC.POL),
SUM(COV.MCP),SUM(PLC.CAS),
COV.CVT
FROM
PLC,COV,EVE
WHERE
PLC.POL = EVE.POL AND
PLC.POL = COV.POL AND
EVE.EXT = 'ADD BILL' AND
EVE.TXC = 'IBIA0102'
GROUP BY COV.CVT)
DATA INITIALLY DEFERRED..........
COUNT(DISTINCT PLC.POL), MQT673 disabled for QR
SUM(COV.MCP) + SUM(PLC.CAS) Query ran for 10.5 seconds
FROM
PLC,COV,EVE MQT673 enabled for QR
WHERE Query ran for 0.91 second
using
PLC.POL = EVE.POL AND
PLC.POL = COV.POL AND
EVE.EXT = 'ADD BILL' AND EVE.TXC = 'IBIA0102' AND COV.CVT = 'P' ;
Chapter 3. SQL performance 51