Trait OptimizerRule 

pub trait OptimizerRule: Debug {
    // Required method
    fn name(&self) -> &str;

    // Provided methods
    fn apply_order(&self) -> Option<ApplyOrder> { ... }
    fn supports_rewrite(&self) -> bool { ... }
    fn rewrite(
        &self,
        _plan: LogicalPlan,
        _config: &dyn OptimizerConfig,
    ) -> Result<Transformed<LogicalPlan>, DataFusionError> { ... }
}

Transforms one LogicalPlan into another which computes the same results, but in a potentially more efficient way.

See notes on Self::rewrite for details on how to implement an OptimizerRule.

To change the semantics of a LogicalPlan, see AnalyzerRule.

Use SessionState::add_optimizer_rule to register additional OptimizerRules.

Required Methods

fn name(&self) -> &str

A human readable name for this optimizer rule

Provided Methods

fn apply_order(&self) -> Option<ApplyOrder>

How should the rule be applied by the optimizer? See comments on ApplyOrder for details.

If returns None, the default, the rule must handle recursion itself

fn supports_rewrite(&self) -> bool

👎Deprecated since 47.0.0:

This method is no longer used

Does this rule support rewriting owned plans (rather than by reference)?

fn rewrite( &self, _plan: LogicalPlan, _config: &dyn OptimizerConfig, ) -> Result<Transformed<LogicalPlan>, DataFusionError>

Try to rewrite plan to an optimized form, returning Transformed::yes if the plan was rewritten and Transformed::no if it was not.

Notes for implementations:

Return the same plan if no changes were made

If there are no suitable transformations for the input plan, the optimizer should simply return it unmodified.

The optimizer will call rewrite several times until a fixed point is reached, so it is important that rewrite return Transformed::no if the output is the same.

Matching on functions

The rule should avoid function-specific transformations, and instead use methods on ScalarUDFImpl and AggregateUDFImpl. Specifically, the rule should not check function names as functions can be overridden, and may not have the same semantics as the functions provided with DataFusion.

For example, if a rule rewrites a function based on the check func.name() == "sum", it may rewrite the plan incorrectly if the registered sum function has different semantics (for example, the sum function from the datafusion-spark crate).

There are still several cases that rely on function name checking in the rules included with DataFusion. Please see #18643 for more details and to help remove these cases.

Implementors

impl OptimizerRule for CommonSubexprEliminate

impl OptimizerRule for DecorrelateLateralJoin

impl OptimizerRule for DecorrelatePredicateSubquery

impl OptimizerRule for EliminateCrossJoin

Eliminate cross joins by rewriting them to inner joins when possible.

Example

The initial plan for this query:

select ... from a, b where a.x = b.y and b.xx = 100;

Looks like this:

Filter(a.x = b.y AND b.xx = 100)
 Cross Join
  TableScan a
  TableScan b

After the rule is applied, the plan will look like this:

Filter(b.xx = 100)
  InnerJoin(a.x = b.y)
    TableScan a
    TableScan b

Other Examples

• ‘select … from a, b where a.x = b.y and b.xx = 100;’
• ‘select … from a, b where (a.x = b.y and b.xx = 100) or (a.x = b.y and b.xx = 200);’
• ’select … from a, b, c where (a.x = b.y and b.xx = 100 and a.z = c.z)
• or (a.x = b.y and b.xx = 200 and a.z=c.z);’
• ‘select … from a, b where a.x > b.y’

For above queries, the join predicate is available in filters and they are moved to join nodes appropriately

This fix helps to improve the performance of TPCH Q19. issue#78

impl OptimizerRule for EliminateDuplicatedExpr

impl OptimizerRule for EliminateFilter

impl OptimizerRule for EliminateGroupByConstant

impl OptimizerRule for EliminateJoin

impl OptimizerRule for EliminateLimit

impl OptimizerRule for EliminateOuterJoin

Attempt to eliminate outer joins.

impl OptimizerRule for ExtractEquijoinPredicate

impl OptimizerRule for ExtractLeafExpressions

impl OptimizerRule for PushDownLeafProjections

impl OptimizerRule for FilterNullJoinKeys

impl OptimizerRule for OptimizeProjections

impl OptimizerRule for OptimizeUnions

impl OptimizerRule for PropagateEmptyRelation

impl OptimizerRule for PushDownFilter

impl OptimizerRule for PushDownLimit

Push down Limit.

impl OptimizerRule for ReplaceDistinctWithAggregate

impl OptimizerRule for RewriteSetComparison

impl OptimizerRule for ScalarSubqueryToJoin

impl OptimizerRule for SimplifyExpressions

impl OptimizerRule for SingleDistinctToGroupBy