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

Still, this second conversion is a conversion from 1208 to 1200 which is somewhat less
expensive than an ASCII conversion (provided that z/OS 1.4 is installed).
In summary, for CHAR columns, not setting DISABLEUNICODE shifts the Unicode
conversion during the Insert from the z/OS server to the workstation client, helping to reduce
class 2 CPU time. For GRAPHIC columns, DISABLEUNICODE has a more subtle effect,
because in one case the class 2 CPU time contains a conversion from UTF-8 to UTF-16, and
in the other case the class 2 CPU time contains a conversion from ASCII to UTF-16 (a Java
application would send all data as UTF-8.)
The same DISABLEUNICODE parameter affects both host variables and SQL statements.
Since DB2 V8 does SQL parsing in Unicode, it becomes more important to avoid setting
DISABLEUNICODE. This is especially true if any of the code points used in the SQL
statement is greater than 127. If all code points are less than 128, CCSID 1208 is equivalent
to ASCII, and no conversion of the SQL statement actually occurs. See “DB2 V8 major and
minor conversion” on page 185 for more details.
Now let us have a look at Unicode conversion for Java clients.
Along with DB2 V8, IBM introduced the Universal Driver for JDBC and SQLJ to replace the
old Legacy JDBC Driver. The Universal Driver does not use DB2 Connect. The Universal
Driver supports both a Type 2 and Type 4 Driver. While the Type 2 Driver is optimally used by
local Java applications running on z/OS, the Type 4 Driver can be used by workstation clients
as well as z/OS clients. The Type 4 Driver uses DRDA protocols.
Since the Universal Driver does not use DB2 Connect, the DISABLEUNICODE parameter is
not applicable. Instead the Universal Type 4 Driver supports a new “UseServerEncoding” data
source property. Unlike the Legacy Driver, the Universal Driver always sends the SQL
statement in UTF-8 no matter how the property is set. The Universal Java Driver is shipped
with DB2 V8 and V7 with PQ8841. Although it can connect to DB2 V7, it is optimized to work
with DB2 V8. Since the Universal Driver always sends the SQL statement in UTF-8, a V7
server has to convert the SQL statement to EBCDIC, and the result is higher class 2 CPU
time.
Because there is no disadvantage to using UseServerEncoding=1, our discussion assumes
that UseServerEncoding=1 is always used.
Figure 4-15 shows the Universal Java Type 2 Driver locally connecting to DB2 V8, first using
an EBCDIC database and then using a Unicode database.
Chapter 4. DB2 subsystem performance 179