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

In October 2003, a new enhancement was shipped to z/OS in PTF UA05789, known as HC3,
that included very significant performance enhancements, especially (but not exclusively) for
conversions between UTF-8 and EBCDIC (or ASCII). The UTF-8 enhancement applies to
both the 31-bit service and the 64-bit service. In order to take advantage of this performance
enhancement, you must rebuild your conversion tables after this PTF has been applied. With
this enhancement, Conversion Services under z/OS 1.4 can be as much as 3.75 times faster
than under z/OS 1.3.
In addition to the UTF-8 enhancement, the 64-bit service implemented some improved
module linkage that gives DB2 V8 an advantage over DB2 V7. Studies have shown that DB2
V8 improves the performance of major conversion over DB2 V7 and that this improvement is
most evident with small strings. With a 10-byte string, V8 is 1.5 times faster. With a 200-byte
string, V8 is only about 15% faster.
zSeries processor hardware
The z/OS Conversion Services take advantage of a number of new hardware instructions that
are faster with the z990 and z890 processors. These instructions are:
► CUTFU - Convert from UTF-8 to UTF-16
► CUUTF - Convert from UTF-16 to UTF-8
► TROO - Translate from One byte to another One byte (used to convert single byte codes)
► TRTO - Translate from Two bytes to One byte (used to convert from UTF-16 to EBCDIC)
► TROT - Translate from One byte to Two bytes (used to convert from EBCDIC to UTF-16)
► TRTT - Translate Two bytes to Two bytes (used to convert between UTF-16 and double
byte EBCDIC)
z/OS understands the term Unicode to be UTF-16, while DB2 for z/OS uses Unicode UTF-8
for the catalog and all CHAR columns within Unicode tables. So, all z/OS Conversion
Services translations between SBCS EBCDIC and UTF-8 require two steps. Step 1 uses the
TROT instruction to convert from EBCDIC to UTF-16, and step 2 uses the CUUTF instruction
to convert from UTF-16 to UTF-8. Conversion in the opposite direction first uses CUTFU and
then TRTO. In other words, UTF-16 is always used to transit between EBCDIC and UTF-8.
Combining these two steps into one step was the key to HC3's improved performance, which
was discussed earlier, but UTF-16 is still used as a transit point.
Conversions involving DBCS make use of the TRTT instruction, and mixed strings involve
some combination of all of these instructions. If the caller need only convert between UTF-8
and UTF-16, only the CUUTF or CUTFU instruction is used, so the performance is faster than
conversions between UTF-8 and EBCDIC or ASCII.
Like many other instructions, the CPU time of these instructions increases in proportion to the
string length. In a workload involving Unicode conversion, the CPU time effects of these
instructions can be high, especially with large strings. The z990 and z890 processors have
provided significant enhancements to the TROO, TROT, TRTO and TRTT instructions,
making them as much as five times faster than the z900 and z800 processors. The larger the
string is, the larger the performance benefit of the z990 and z890 processors.
Studies have shown that the z990 reduces the conversion CPU time using V7 for 10 byte
strings by 1.5 times. This is a typical z990 improvement that we have measured for most
applications. This increases to a two times improvement for 200 byte strings, which is even
better. Performance of other string lengths may be inter- or extrapolated from 10-byte and
200-byte strings. We see similar improvements in DB2 V8.
186 DB2 UDB for z/OS Version 8 Performance Topics