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

This conflicts with the RISK_PREMIUM_NJ, RISK_PREMIUM_SERIAL, and
PARTITIONING_SCHEME_SHARING settings. Use this CQD when possible. Use the risk
premium settings rarely, when specific premiums need to be set differently to address
specific issues.
If overall this CQD is working well but you have outliers, such as poor nested join plans
or inappropriate serial plans, you could use the individual CQDs at a finer granularity,
such as at a query level, to get better plans.
Conflicts/Synergies
Sometimes the cardinality underestimation, compared to the actual row counts, resulting
in a nested join or serial plan being chosen when it shouldn’t have been, may be due to not
enough, or inaccurate, histogram statistics information available to the optimizer. So, first
and foremost, histogram statistics should be kept up to date along with the multi-column
statistics that the optimizer may warn about. However, cardinality underestimations may
still happen at higher levels of an execution plan.
Addressing the real
problem
Neoview Release 2.4Introduced in release
Not applicableDeprecated in release
SUBQUERY_UNNESTING
Influencing Query PlansCategory
Controls the optimizer’s ability to transform nested sub-queries into regular join trees.Description
Subquery un-nesting is considered.‘ON’
Subquery un-nesting is disabled.‘OFF’
The default value is ‘ON’.
Values
Use this control to disable subquery un-nesting in the rare situation when un-nesting results
in an inefficient query execution plan
Usage
Not applicableProduction usage
In general, subquery un-nesting results in more efficient execution plans for queries with
nested sub-queries. Use only as a workaround for observed problems due to un-nesting.
Impact
QueryLevel
Not applicableConflicts/Synergies
Not applicableAddressing the real
problem
Neoview Release 2.2Introduced in release
Not applicableDeprecated in release
28 Optimizer