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

2 Managing Adaptive Segmentation
This section describes these CQDs that are used for managing adaptive segmentation:
• “DEFAULT_DEGREE_OF_PARALLELISM” (page 13)
• “PARALLEL_NUM_ESPS” (page 13)
DEFAULT_DEGREE_OF_PARALLELISM
Influencing Query PlansCategory
Defines the minimum size of the adaptive segment; the number of processors available for
query operator parallelism. The optimizer may choose an adaptive segment size that is
equal to, or the multiple of, the value of this CQD, depending on the maximum estimated
resource consumed by any single operator in the query. The optimizer may also decide to
run the query with no parallelism if the resource consumption estimate is very low.
Description
Unsigned Integer
The default value is ‘16’.
Values
For systems running at higher levels of concurrency with workloads that include a large
number of small queries, reducing the default degree of parallelism may help achieve
higher throughput.
With the default of 16, for 32p systems, adaptive segmentation can use two 16p virtual
segments to execute queries that do not require a degree of parallelism of 32. The default
setting can be changed to 8 for a 16p system, to allow adaptive segmentation to leverage
a lower degree of parallelism.
Usage
Not applicableProduction usage
Lowering the value of this CQD can increase the throughput of high concurrency small
query workloads, but has the potential disadvantage of increasing the elapsed time for
some of the longer running queries that leverage adaptive segmentation.
Impact
System. There may be scenarios where you want to influence the degree of adaptive
segmentation parallelism only for a certain set of queries and use it at the service level.
Level
Not applicableConflicts/Synergies
Not applicableAddressing the real
problem
Neoview Release 2.2Introduced in release
Not applicableDeprecated in release
PARALLEL_NUM_ESPS
Influencing Query PlansCategory
Controls the maximum number of parallel ESPs that work on a particular operation, like
a join.
Description
The maximum number of ESPs that should be used for a
particular operation. The value must be less than the number of
CPUs in the cluster.
Unsigned Integer
The compiler calculates the number of ESPs to be used.‘SYSTEM’
The default value is ‘SYSTEM’.
Values
Used to control the maximum degree of parallelism for a query. This could be useful to
limit the number of resources (CPU and memory) any single query can use.
Usage
Not applicableProduction usage
DEFAULT_DEGREE_OF_PARALLELISM 13