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

4.7.1 Performance
The improvements in Unicode conversion come from three sources. Each of these sources
affects different facets of conversion performance, such as the type of characters, and the
length of the character strings. The three sources are:
► DB2 V8 major and minor conversion: Improves the performance of all types of
conversions, but the improvements are most dramatic with English alphanumeric
characters because DB2 does not need to invoke the Unicode conversion service.
► z/OS Conversion Services: z/OS Release 1.4 implemented an enhancement to z/OS
Conversion Services with PTF UA05789: This enhancement, referred to as HC3, helps the
performance of both DB2 V7 and V8.
► zSeries processor hardware: The z900 model introduced some new Unicode hardware
instructions that are simulated by the z/OS Conversion Services on older processors. In
addition, the speed of a z990 engine is approximately 50% faster than the z900 Turbo, but
when it comes to the Unicode conversion of large strings, the z990 hardware is twice as
fast (in this book, we refer to the z900 Turbo model).
Figure 4-19 summarizes the step by step improvements in conversion performance each of
these sources have made. For these measurements, a single table scan of 1 million rows was
used, using a single cursor with no predicates. The table was defined using 20 VARCHAR
columns per row with 10 characters per column.
Figure 4-19 Conversion performance overview
Note that the table is not drawn exactly to scale, but it does show the progressive gains in
performance that have been achieved.
The first bar represents DB2 V7 running on z/OS 1.3 with EBCDIC host variables and
database. CCSID conversion is done here by DB2 using SYSIBM.SYSSTRINGS. Next, we
see a huge jump in CPU time as we ask DB2 V7 to use Unicode. DB2 V7 now must invoke
z/OS Conversion Services for any conversion to and from Unicode. By simply moving to z/OS
1.4, we see quite a improvement in CPU. This is primarily due to advancements in the z/OS
Conversion Services that dramatically improved the performance of (but not exclusively)
conversions between UTF-8 and EBCDIC (or ASCII). The next step in performance is
184 DB2 UDB for z/OS Version 8 Performance Topics
Conversion performance overview
DB2V7, z900, z/OS 1.3, EBCDIC hostvars and database
+UTF-8
database
+ z/OS 1.4
+ z990
+ DB2V8 (assuming non-alphanumeric)
+ minor conversion (assuming alphanumeric)
+ convert the hostvars to UTF-8 (eliminate conversion)
CPU time