Struct mz_transform::predicate_pushdown::PredicatePushdown

pub struct PredicatePushdown {
    recursion_guard: RecursionGuard,
}

Pushes predicates down through other operators.

Fields

recursion_guard: RecursionGuard

Implementations

impl PredicatePushdown

pub fn action(
    &self,
    relation: &mut MirRelationExpr,
    get_predicates: &mut HashMap<Id, HashSet<MirScalarExpr>>
) -> Result<(), TransformError>

Predicate pushdown

This method looks for opportunities to push predicates toward sources of data. Primarily, this is the Filter expression, and moving its predicates through the operators it contains.

In addition, the method accumulates the intersection of predicates applied to each Get expression, so that the predicate can then be pushed through to a Let binding, or to the external source of the data if the Get binds to another view.

pub fn push_filters_through_map(
    &self,
    scalars: &Vec<MirScalarExpr>,
    predicates: &mut Vec<MirScalarExpr>,
    input_arity: usize,
    all_errors: bool
) -> Result<(Vec<MirScalarExpr>, Vec<MirScalarExpr>), TransformError>

Computes “safe” predicates to push through a Map.

In the case of a Filter { Map {…} }, we can always push down the Filter by inlining expressions from the Map. We don’t want to do this in general, however, since general inlining can result in exponential blowup in the size of expressions, so we only do this in the case where we deem the referenced expressions “safe.” See the comment above can_inline for more details. Note that this means we can always push down filters that only reference input columns.

Returns the predicates that can be pushed down, followed by ones that cannot.

pub fn push_filters_through_flat_map(
    predicates: &mut Vec<MirScalarExpr>,
    input_arity: usize
) -> (Vec<MirScalarExpr>, Vec<MirScalarExpr>)

Computes “safe” predicate to push through a FlatMap.

In the case of a Filter { FlatMap {…} }, we want to push through all predicates that (1) are not literal errors and (2) have support exclusively in the columns provided by the FlatMap input.

Returns the predicates that can be pushed down, followed by ones that cannot.

fn extract_equal_or_both_null(
    s: &mut MirScalarExpr,
    relation_type: &RelationType
) -> Option<(MirScalarExpr, MirScalarExpr)>

If s is of the form (isnull(expr1) && isnull(expr2)) || (expr1 = expr2), or (decompose_is_null(expr1) && decompose_is_null(expr2)) || (expr1 = expr2), extract expr1 and expr2.

fn extract_equal_or_both_null_inner(
    or_arg1: &MirScalarExpr,
    or_arg2: &MirScalarExpr,
    relation_type: &RelationType
) -> Option<(MirScalarExpr, MirScalarExpr)>

fn extract_reduced_conjunction_terms(
    s: MirScalarExpr,
    relation_type: &RelationType
) -> Vec<MirScalarExpr>

Reduces the given expression and returns its AND-ed terms.

fn can_inline(s: &MirScalarExpr, input_arity: usize) -> bool

Defines a criteria for inlining scalar expressions.

fn is_safe_leaf(s: &MirScalarExpr, input_arity: usize) -> bool

Trait Implementations

impl CheckedRecursion for PredicatePushdown

fn recursion_guard(&self) -> &RecursionGuard

Extracts a reference to the recursion guard embedded within the type.

fn checked_recur<F, T, E>(&self, f: F) -> Result<T, E> where
    F: FnOnce(&Self) -> Result<T, E>,
    E: From<RecursionLimitError>, 

Checks whether it is safe to recur and calls f if so.

fn checked_recur_mut<F, T, E>(&mut self, f: F) -> Result<T, E> where
    F: FnOnce(&mut Self) -> Result<T, E>,
    E: From<RecursionLimitError>, 

Like CheckedRecursion::checked_recur, but operates on a mutable reference to Self.

impl Debug for PredicatePushdown

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for PredicatePushdown

fn default() -> PredicatePushdown

Returns the “default value” for a type.

impl Transform for PredicatePushdown

fn transform(
    &self,
    relation: &mut MirRelationExpr,
    _: TransformArgs<'_>
) -> Result<(), TransformError>

Transform a relation into a functionally equivalent relation.

fn debug(&self) -> String

A string describing the transform.