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

Table UDF – Cardinality Option
SELECT .....
FROM ORDER A , TABLE(TUDF(100000 )
CARDINALITY 100000) AS B
WHERE A.cust_key = B.int_key
AND A.order_key BETWEEN 1 AND 1500000 ;
Access path is
changed from
NLJ to HBJ
with correct
cardinality
value 100000
Figure 3-37 Table UDF - Cardinality option
Figure 3-38 shows the measurements with no block fetch and with block fetch.
Table UDF – Block Fetch Support
seconds
seconds
Figure 3-38 Table UDF - Block fetch support
300
250
200
150
100
150
100
50
0
50
0
10 100000
cardinality
Non block fetch Block fetch
Elapsed
CPU
Elapsed
CPU
Block Fetch support
Materialize the rows from a table UDF into a workfile at UDF open call
CPU improvement by avoiding task switches.
Native Measurement using a simple Table UDF
Measured in 10 to 1M rows
About 40% CPU time was saved using Block Fetch support or a simple Table UDF
on Freeway Turbo
Chapter 3. SQL performance 85