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

► More rows per one SQL statement (10 rows per multi-row statement results in significant
improvement)
► Fewer indexes processed in table
Table 3-1 provides a summary of the measurements discussed for multi-row operations
processing 100,000 rows in a non-partitioned table space with a 100,000 row table, 26
columns, and 1 index.
Table 3-1 Class 1 CPU time (sec.) to process 100,000 rows
Type of MR operation
loopsxrows per SQL
In general, for single-row processing DB2 V8 uses more CPU time, with the exception of the
insert operation.
3.1.6 Recommendation
Explicit multi-row FETCH, INSERT, cursor UPDATE, and cursor DELETE in local
environments can improve performance with a reduction of CPU time (between 25% and 40%
in the measurements processing 10 rows per SQL statement) if a program processes a
considerable number of rows. Depending on each particular case, a number between 10 rows
and 100 rows per SQL can be a good starting point for multi-row operations.
This option requires definition of host variable array declaration of the cursor with rowset
positioning and the text of the SQL to specify the rowset size.
You also have to change your coding on how to do cursor processing. You have to look at how
many rows are returned on a FETCH via SQERRD3 flag in the SQLCA (or the equivalent
ROW_COUNT when using GET DIAGNOSTICS).
For existing programs it is worth evaluating the benefits provided vs. the cost of recoding the
programs. The extra storage needed for multi-row operations is allocated in the allied address
space, or stored procedure, or DDF.
A variable array has to be explicitly declared. Example 3-2, extracted from the DB2
Application Programming and SQL Guide, SC18-7415, shows declarations of a fixed-length
character array and a varying-length character array in COBOL.
Example 3-2 COBOL array declaration
01 OUTPUT-VARS.
05 NAME OCCURS 10 TIMES.
49 NAME-LEN PIC S9(4) COMP-4 SYNC.
49 NAME-DATA PIC X(40).
38 DB2 UDB for z/OS Version 8 Performance Topics
FETCH INSERT FETCH/UPDATE FETCH/DELETE
V7 single-row 1.09 2.92 2.5 3.68
V8 single-row 1.15 2.73 2.79 3.81
50kx2 1.02 2.51 2.8 3.71
10kx10 0.64 1.94 1.88 2.76
1kx100 0.55 1.8 1.57 2.42
100x1k 0.54 1.79 1.51 2.37
10x10k 0.54 1.79 1.51 2.35