SQL/MX 2.x Reference Manual (H06.04+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—540440-003
10-54
Query Optimization and Performance
Query Optimization and Performance
These attributes enable NonStop SQL/MX to optimize query execution:
Attribute Setting
ATTEMPT_ASYNCHRONOUS_
ACCESS
Set to ON or OFF. When set to ON, the optimizer
generates plans that access multiple partitions
asynchronously (that is, at the same time). With
asynchronous access, the optimizer does not use
ESPs to access the partitions in parallel.
This setting also affects whether stream access to a
table with partitions is allowed. See Stream Access
Restrictions on page 2-192.
For additional information about this setting, see the
SQL/MX Query Guide.
The default is ON.
ATTEMPT_ESP_PARALLELISM Set to ON, OFF, or SYSTEM. If ON, the optimizer
generates and considers plans that use ESP
parallelism for all operators that can use ESP
parallelism. If OFF, the optimizer never generates
and considers plans that use ESP parallelism. If
SYSTEM, the optimizer determines on an operator-
by-operator basis when to generate and consider
plans that use ESP parallelism.
For additional information about this setting, see the
SQL/MX Query Guide.
The default is SYSTEM.
CROSS_PRODUCT_CONTROL Set to ON or OFF. ON reduces compile time by
eliminating query plans that include unnecessary
and expensive cross-products (joins without join
predicates).
For additional information about this setting, see the
SQL/MX Query Guide.
The default is ON.
DATA_FLOW_OPTIMIZATION Set to ON or OFF. Reduces compile time by not
considering some query plans that have relatively
high data flow rates.
The default is ON, resulting in improvement in
compile time without impacting plan quality.