Neoview Control Query Default (CQD) Reference Guide (R2.5)

Neoview Release 2.3Introduced in release
Not applicableDeprecated in release
USTAT_MIN_ROWCOUNT_FOR_SAMPLE
Update Statistics and ReorgCategory
Sets the minimum rows that need to be in a table before sampling is used to update statistics
for that table. If a table has a fewer rows than the value of this CQD, the SAMPLE option
is silently ignored when performing update statistics.
Description
1 through max unsigned
integer
The default value is 10000.
Values
Influences for what tables sampling is used for histogram statistics generation. If the setting
is smaller, then more tables qualify for sampling. If the setting is larger, then fewer tables
qualify for sampling. Sampling can result in faster update statistics run times. But for
smaller tables, it can also result in poor histogram accuracy which could result in poor
query plans.
Usage
Not applicableProduction usage
Setting this CQD to a smaller value means that sampling is used for tables with fewer rows,
when the SAMPLE option is specified as part of update statistics. This can result in less
accurate histograms and poor query plans, because the sample size may be too small to
generate good estimates for histograms.
Setting this CQD to a larger value can result in sampling not being used for many tables
and therefore longer update statistics run times. However, these tables may also have more
accurate histograms.
Impact
SystemLevel
Not applicableConflicts/Synergies
Not applicableAddressing the real
problem
Neoview Release 2.0Introduced in release
Not applicableDeprecated in release
USTAT_NECESSARY_SAMPLE_MAX
Update Statistics and ReorgCategory
Sets the maximum size of a sample when update statistics automation or update statistics
with the NECESSARY keyword is used.
For the NECESSARY keyword and automation, update statistics always samples, and the
sample percent is determined using this equation:
MINOF(HIST_DEFAULT_SAMPLE_RATIO + CV * USTAT_AUTO_CV_SAMPLE_SLOPE,
10%), limited to USTAT_NECESSARY_SAMPLE_MAX rows.
Description
1 through max unsigned
integer
The default value is 5000000.
Values
Use this CQD to influence the maximum size of the sample, when sampling is used to
update statistics for a table, thereby influencing the time it takes to run update statistics.
The smaller the maximum sample size, the faster update statistics runs for larger tables.
Usage
Not applicableProduction usage
USTAT_MIN_ROWCOUNT_FOR_SAMPLE 19