public Interface Optimizer

Property name for controlling whether to do join order optimization.

Maximum size of dynamically created materialized rows. Caching large results use lot of memory and can cause stack overflow. See DERBY-634

Property name for controlling the maximum size of memory (in KB) the optimizer can use for each table. If an access path takes memory larger than that size for a table, the access path is skipped. Default is 1024 (KB).

Module name for the monitor's module locating system.

Property name for controlling whether the optimizer ever times out while optimizing a query and goes with the best plan so far.

Indicates a "normal" plan that is not optimized to do sort avoidance

Property name for controlling whether to do rule-based optimization, as opposed to cost-based optimization.

Indicates a sort-avoidance plan

Property name for disabling statistics use for all queries.

Consider the cost of the given optimizable. This method is like costOptimizable, above, but it is used when the Optimizable does not need help from the optimizer in costing the Optimizable (in practice, all Optimizables except FromBaseTable use this method. Caller is responsible for pushing all predicates which can be evaluated prior to costing.

Parameters

optimizable:Optimizable

The Optimizable

predList:OptimizablePredicateList

The OptimizablePredicateList to apply

estimatedCost:CostEstimate

The estimated cost of the given optimizable

outerCost:CostEstimate

The cost of the tables outer to the one being optimizer - tells how many outer rows there are.

Exceptions

StandardException:

Thrown on error

Cost the current Optimizable with the specified OPL. Caller is responsible for pushing all predicates which can be evaluated prior to costing.

Parameters

optimizable:Optimizable

The Optimizable

td:TableDescriptor

TableDescriptor of the Optimizable

cd:ConglomerateDescriptor

The ConglomerateDescriptor for the conglom to cost (This should change to an object to represent access paths, but for now this is OK).

predList:OptimizablePredicateList

The OptimizablePredicateList to apply

outerCost:CostEstimate

The cost of the tables outer to the one being optimizer - tells how many outer rows there are.

Exceptions

StandardException:

Thrown on error

Cost the current permutation. Caller is responsible for pushing all predicates which can be evaluated prior to costing.

Exceptions

StandardException:

Thrown on error

Return the DataDictionary that the Optimizer is using. This is useful when an Optimizable needs to call optimize() on a child ResultSetNode.

Returns:DataDictionary

DataDictionary DataDictionary that the Optimizer is using.

Get the final estimated cost of the optimized query. This should be the cost that corresponds to the best overall join order chosen by the optimizer, and thus this method should only be called after optimization is complete (i.e. when modifying access paths).

Gets a join strategy by number (zero-based).

Gets a join strategy by name. Returns null if not found. The look-up is case-insensitive.

Get the level of this optimizer.

Returns:int

The level of this optimizer.

Returns:int

the maximum number of bytes to be used per table.

Iterate through the "decorated permutations", returning false when they are exhausted. NOTE - Implementers are responsible for hiding tree pruning of access methods behind this method call.

Returns:boolean

boolean True - An optimizable decorated permutation remains. False - Decorated permutations are exhausted.

Exceptions

StandardException:

Thrown on error

Iterate through the permutations, returning false when the permutations are exhausted. NOTE - Implementers are responsible for hiding tree pruning of permutations behind this method call.

Returns:boolean

boolean True - An optimizable permutation remains. False - Permutations are exhausted.

Exceptions

StandardException:

Thrown on error

Get the number of join strategies supported by this optimizer.

Get the ith (0-based) Optimizable being considered by this Optimizer.

Get the number of optimizables being considered by this Optimizer.

Get the estimated cost of the optimized query

Modify the access path for each Optimizable, as necessary. This includes things like adding result sets to translate from index rows to base rows.

Exceptions

StandardException:

Thrown on error

Prepare for another round of optimization. This method is called before every "round" of optimization, where we define a "round" to be the period between the last time a call to getOptimizer() (on either a ResultSetNode or an OptimizerFactory) returned _this_ Optimizer and the time a call to this Optimizer's getNextPermutation() method returns FALSE. Any re-initialization of state that is required before each round should be done in this method.

Set the estimated number of outer rows - good for optimizing nested optimizables like subqueries and join nodes.

Get the maximum number of estimated rows touched in a table before we decide to open the table with table locking (as opposed to row locking.

Tells whether any of the tables outer to the current one has a uniqueness condition on the given predicate list, and if so, how many times each unique key can be seen by the current table.

Parameters

predList:OptimizablePredicateList

The predicate list to check

Returns:double

<= 0 means there is no uniqueness condition > 0 means there is a uniqueness condition on an outer table, and the return value is the reciprocal of the maximum number of times the optimizer estimates that each unique key will be returned. For example, 0.5 means the optimizer thinks each distinct join key will be returned at most twice.

Exceptions

StandardException:

Thrown on error

Process (i.e. add, load, or remove) current best join order as the best one for some outer query or ancestor node, represented by another Optimizer or an instance of FromTable, respectively. Then iterate through our optimizableList and tell each Optimizable to do the same. See Optimizable.updateBestPlan() for more on why this is necessary.

Parameters

action:short

Indicates whether to add, load, or remove the plan

planKey:Object

Object to use as the map key when adding/looking up a plan. If this is an instance of Optimizer then it corresponds to an outer query; otherwise it's some Optimizable above this Optimizer that could potentially reject plans chosen by this Optimizer.

If statistics should be considered by the optimizer while optimizing a query. The user may disable the use of statistics by setting the property derby.optimizer.useStatistics or by using the property useStatistics in a query.

See Also

USE_STATISTICS