Table of Contents
Advertisement
Improving your queries
Setting query optimization options
458
•
This option controls the collection of timing statistics
QUERY_TIMING
on subqueries and some other repetitive functions in the query engine.
Normally it should be
the cost of timing every subquery execution can be very expensive in
terms of performance.
By adjusting the following options you can influence the speed at which
queries are processed.
•
AGGREGATION_ALGORITHM_PREFERENCE
algorithms for processing an aggregate (
functions). This option is designed primarily for internal use; do not use it
unless you are an experienced database administrator. See the Adaptive
Server IQ Reference Manual for details.
•
AGGREGATION_CUTOFF
more efficient internal storage type for
default is 10. The internal storage type is slower, but avoids risking
overflows.
•
INDEX_PREFERENCE
Adaptive Server IQ optimizer normally chooses the best index available to
process local
WHERE
done within an IQ index. This option is used to override the optimizer
choice for testing purposes; under most circumstances it should not be
changed.
•
JOIN_ALGORITHM_PREFERENCE
when processing joins. This option is designed primarily for internal use;
do not use it unless you are an experienced database administrator. See the
Adaptive Server IQ Reference Manual for details.
•
JOIN_OPTIMIZATION
Server IQ optimizes the join order to reduce the size of intermediate results
and sorts and to balance the system load. When it is
determined by the order of the tables in the
statement. (The left-most table becomes the outer table of the topmost
join.) This option should be
when you don't know optimum join order for a multi-table join query, or
when you cannot alter queries.
because for very short correlated subqueries
OFF
GROUP BY
Specifies at which precision level to use a
or
SUM
Sets the index to use for query processing. The
clause predicates and other operations which can be
Controls the choice of algorithms
When this option is
ON
FROM
whenever queries are ad hoc and untried,
ON
Controls the choice of
,
,
DISTINCT
SET
calculations. The
AVG
(the default), Adaptive
, the join order is
OFF
clause of the
SELECT
Advertisement
Table of Contents
