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

3.8.2 Performance
We show three examples.
Example 3-10 shows passing a multiplier value.
Example 3-10 User-defined table function (1/3)
SELECT *
FROM TABLE(TUDF(1) CARDINALITY MULTIPLIER 30) AS X;
If the cardinality was specified to be 1 when TUDF was defined, DB2 assumes that the
expected number of rows to be returned is 30 (30 x 1) for this invocation of user-defined table
function TUDF.
Example 3-11 shows a different multiplier.
Example 3-11 User-defined table function (2/3)
SELECT R
FROM TABLE(TUDF(2) CARDINALITY MULTIPLIER 0.3) AS X;
If the cardinality was specified to be 100 when TUDF was defined, DB2 assumes that the
expected number of rows to be returned by TUDF is 30 (0.3 x 100).
Example 3-12 shows passing an absolute value.
Example 3-12 User-defined table function (3/3)
SELECT R
FROM TABLE(TUDF(3) CARDINALITY 30) AS X;
DB2 assumes that the expected number of rows to be returned by TUDF is 30, regardless of
the value in the table function.
For more details on the specification of CARDINALITY and CARDINALITY MULTIPLIER, see
the table-UDF-cardinality-clause section in DB2 UDB for z/OS Version 8 SQL Reference,
SC18-7426.
Table UDFs are driven by Content Manager in all members of the DB2 family:
► Content Manager uses Text Information Extender/Text Extender to perform text search
► Results from the table UDF are joined with base or other tables
Measurements show the performance improvements for the table UDF as a result of:
► Cardinality option:
– User/Extender can specify the cardinality of the table UDF in SQL levels
– Better access path selection
► Table UDF block fetch support
– Materialize the rows from a table UDF into a work file at UDF open statement
► Table UDF join predicates become sortable
– Retrofitted into V7 as PQ54042
Figure 3-37 shows that specifying the cardinality option in SQL reduced both the elapsed and
CPU time.
84 DB2 UDB for z/OS Version 8 Performance Topics