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

6.3.2 Conclusion
We measured the CPU time for both LOAD and UNLOAD using three variations (internal
format, external format, and delimited format) and our tested hardware was a z900 Turbo.
There are 10 columns, including 4 CHAR, 1 VARCHAR, 3 DECIMAL, 1 SMALLINT and 1
DATE and no index exists in our test table. Delimited requires using external format for
numeric. For example, INTEGER or SMALLINT is treated as if they were INTEGER
EXTERNAL, and DECIMAL is treated as DECIMAL EXTERNAL. DATE is always treated as
EXTERNAL, which causes the DATE fields to always have a large impact on UNLOAD
performance, even though you might prefer internal format in several cases like migrating the
DATE data to a different table.
The results are shown in Table 6-1.
Table 6-1 Delimited Load and Unload CPU comparisons
External is more expensive than internal because DECIMAL and SMALLINT data in external
format has to contain a character string that represents a number in specific forms. However,
it should be noted that external performs significantly worse than internal, especially with
UNLOAD.
When compared to LOAD and UNLOAD of external undelimited format, delimited format
LOAD and UNLOAD have more impact on performance. It makes sense because in UNLOAD
delimited format DB2 has to build the output data to be either in character string or numeric
external format, and also has to add column delimiters (default is comma) and a double
quotation mark (") for the character string and a period (.) for the decimal point character.
LOAD costs more because of the need to scan the VARCHAR data to define the length.
In our test UNLOAD of external format significantly increased CPU time compared to internal
format.
6.4 RUNSTATS enhancements
In this section we first show some performance improvements in executing RUNSTATS with
different options, and then we discuss the new function which allows us to gather distribution
statistics.
6.4.1 General performance improvements
Table 6-2 shows the measurements for RUNSTATS of a table with 10 million rows and 6
indexes.
The measurements were implemented on a IBM z900 Series 2064 processor.
Table 6-2 Summary of RUNSTATS improvements
RUNSTATS
DB2 V7 (sec.) DB2 V8 (sec.) Delta CPU Delta ET
option
CPU Elapsed CPU Elapsed % %
272 DB2 UDB for z/OS Version 8 Performance Topics
internal external delimited delta (del/ext)
LOAD (sec.) 11.41 16.3 26.5 +63%
UNLOAD (sec.) 13.3 30.57 34.75 +14%
TABLESPACE 15.7 39 8.6 40 -45.23 2.57