SQL/MX 2.x Reference Manual (H06.10+, J06.03+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—544517-008
10-57
Query Optimization and Performance
Query Optimization and Performance
These attributes enable NonStop SQL/MX to optimize query execution:
Attribute Setting
ALLOW_DP2_ROW_SAMPLING Set to SYSTEM, ON, or OFF. When a SQL/MX
query contains a SAMPLE clause, this attribute
determines whether the sampling operation should
be done by DP2 or by the SQL/MX Executor. When
set to SYSTEM, the sampling is done by DP2 for
sample percentages of up to 5%. When set to ON,
the sampling is done by DP2 for sample
percentages of up to 50%. When set to OFF, the
sampling is done by the SQL/MX Executor and not
by the DP2.
For additional information about this setting, see the
SQL/MX Query Guide.
The default is SYSTEM.
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 2-214.
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.