Module filter_pushdown 

Filter Pushdown Optimization Process

The filter pushdown mechanism involves four key steps:

1. Optimizer Asks Parent for a Filter Pushdown Plan: The optimizer calls ExecutionPlan::gather_filters_for_pushdown on the parent node, passing in parent predicates and phase. The parent node creates a FilterDescription by inspecting its logic and children’s schemas, determining which filters can be pushed to each child.
2. Optimizer Executes Pushdown: The optimizer recursively pushes down filters for each child, passing the appropriate filters (Vec<Arc<dyn PhysicalExpr>>) for that child.
3. Optimizer Gathers Results: The optimizer collects FilterPushdownPropagation results from children, containing information about which filters were successfully pushed down vs. unsupported.
4. Parent Responds: The optimizer calls ExecutionPlan::handle_child_pushdown_result on the parent, passing a ChildPushdownResult containing the aggregated pushdown outcomes. The parent decides how to handle filters that couldn’t be pushed down (e.g., keep them as FilterExec nodes).

See also datafusion/physical-optimizer/src/filter_pushdown.rs.

Structs

ChildFilterDescription

Describes filter pushdown for a single child node.

ChildFilterPushdownResult

The result of pushing down a single parent filter into all children.

ChildPushdownResult

The result of pushing down filters into a child node.

FilterDescription

Describes how filters should be pushed down to children.

FilterPushdownPropagation

The result of pushing down filters into a node.

PushedDownPredicate

The result of a plan for pushing down a filter into a child node. This contains references to filters so that nodes can mutate a filter before pushing it down to a child node (e.g. to adjust a projection) or can directly take ownership of filters that their children could not handle.

Enums

FilterPushdownPhase

PushedDown

Discriminant for the result of pushing down a filter into a child node.