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

6.4.4 Performance
► ST01WKnn: You need to specify the data set name for the temporary data sets of sort
input and output when collecting statistics on at least one data-partitioned secondary
index.
► STATWKnn: You need to specify the data set name for the temporary data sets of sort
input and output when collecting distribution statistics for column groups.
Note: To calculate the approximate size (in bytes) of the ST01WKnn data set, use the
following formula:
2 × (maximum record length × numcols × (count + 2) × number of indexes)
The values in the formula are as follows:
► Maximum record length: The maximum length of the SYSCOLDISTATS record on
which RUNSTATS is to collect frequency statistics. You can obtain this value from the
RECLENGTH column in SYSTABLES.
► Numcols: The number of key columns to concatenate when you collect frequent values
from the specified index.
► Count: The number of frequent values that RUNSTATS is to collect.
When you plan to use distribution statistics, make sure that the following maintenance is
applied for correct functionality and good performance:
► PTF UQ88754 for APAR PQ88375 provides the right value of cardinality for partitioned
table spaces.
► PTF UQ91099 for APAR PQ87509 is required for correctness of frequency values.
► PTF UQ93177 for APAR PQ90884 is required for better (200%) performance.
DSTATS performance comparison of V7 and V8 with PQ90884
In this test we first run RUNSTATS in V7 followed by the standalone DSTATS tool. We
measure class 1 elapsed and CPU time and get the total time of both. In the second case we
measure V8 RUNSTATS with distribution statistics where we collect equivalent statistics to
those taken in V7 with the DSTATS tool. Before running this case we have applied the PTF for
PQ90884.
We use an internal query workload and the test table contains about 931k rows. The
description of the test environment is:
► DB2 V7 and V8 (non-data sharing)
► Table: 1 test table in 1 table space
► Number of pages: 77601
► Number of rows: 931,174
► Number of indexes: 4 (1 partitioned index, 3 non-partitioned indexes)
► Number of partitions of table space: 6
► 2 columns are non-indexed columns (used for statistics)
– Column1 cardinality=15104
– Column2 cardinality=24
To explain our test case more clearly, let us show you a part of our control statements for
testing. We have done equivalent RUNSTATS in V7 and V8, and we have taken equivalent
statistics in V7 with the DSTATS tool, and in V8 with RUNSTATS. We are specifying 2 columns
for statistics and both are non-indexed columns. The description of the statistics is:
Chapter 6. Utilities 275