perf(optimizer): convert filter predicate to CNF to push through join

src/daft-algebra/src/boolean.rs

@@ -1,4 +1,6 @@
-use common_treenode::{TreeNode, TreeNodeRecursion};
+use std::sync::Arc;
+
+use common_treenode::{Transformed, TreeNode, TreeNodeRecursion};
 use daft_dsl::{Expr, ExprRef, Operator};
 
 pub fn split_conjunction(expr: &ExprRef) -> Vec<ExprRef> {
@@ -22,3 +24,161 @@ pub fn split_conjunction(expr: &ExprRef) -> Vec<ExprRef> {
 pub fn combine_conjunction<T: IntoIterator<Item = ExprRef>>(exprs: T) -> Option<ExprRef> {
     exprs.into_iter().reduce(|acc, e| acc.and(e))
 }
+
+/// Converts a boolean expression to conjunctive normal form (AND of ORs)
+pub fn to_cnf(expr: ExprRef) -> ExprRef {
+    let dnf_form = to_dnf(expr.not()).not();
+
+    apply_de_morgans(dnf_form).data
+}
+
+/// Converts a boolean expression to disjunctive normal form (OR of ANDs)
+pub fn to_dnf(expr: ExprRef) -> ExprRef {
+    let dm_expr = apply_de_morgans(expr).data;
+
+    // apply distributive property recursively
+    dm_expr
+        .transform_down(|e| {
+            Ok(match e.as_ref() {
+                Expr::BinaryOp {
+                    op: Operator::And,
+                    left,
+                    right,
+                } => {
+                    if let Expr::BinaryOp {
+                        op: Operator::Or,
+                        left: right_left,
+                        right: right_right,
+                    } = right.as_ref()
+                    {
+                        // (x & (y | z)) -> ((x & y) | (x & z))
+                        Transformed::yes(Arc::new(Expr::BinaryOp {
+                            op: Operator::Or,
+                            left: Arc::new(Expr::BinaryOp {
+                                op: Operator::And,
+                                left: left.clone(),
+                                right: right_left.clone(),
+                            }),
+                            right: Arc::new(Expr::BinaryOp {
+                                op: Operator::And,
+                                left: left.clone(),
+                                right: right_right.clone(),
+                            }),
+                        }))
+                    } else if let Expr::BinaryOp {
+                        op: Operator::Or,
+                        left: left_left,
+                        right: left_right,
+                    } = left.as_ref()
+                    {
+                        // ((x | y) & z) -> ((x & z) | (y & z))
+                        Transformed::yes(Arc::new(Expr::BinaryOp {
+                            op: Operator::Or,
+                            left: Arc::new(Expr::BinaryOp {
+                                op: Operator::And,
+                                left: left_left.clone(),
+                                right: right.clone(),
+                            }),
+                            right: Arc::new(Expr::BinaryOp {
+                                op: Operator::And,
+                                left: left_right.clone(),
+                                right: right.clone(),
+                            }),
+                        }))
+                    } else {
+                        Transformed::no(e)
+                    }
+                }
+                _ => Transformed::no(e),
+            })
+        })
+        .unwrap()
+        .data
+}
+
+/// Transform boolean expression by applying De Morgan's law + eliminate double negations recursively
+fn apply_de_morgans(expr: ExprRef) -> Transformed<ExprRef> {
+    expr.transform_down(|e| {
+        Ok(match e.as_ref() {
+            Expr::Not(ne) => match ne.as_ref() {
+                // !x -> x
+                Expr::Not(nne) => Transformed::yes(nne.clone()),
+                // !(x & y) -> ((!x) | (!y))
+                Expr::BinaryOp {
+                    op: Operator::And,
+                    left,
+                    right,
+                } => Transformed::yes(Arc::new(Expr::BinaryOp {
+                    op: Operator::Or,
+                    left: left.clone().not(),
+                    right: right.clone().not(),
+                })),
+                // !(x | y) -> ((!x) & (!y))
+                Expr::BinaryOp {
+                    op: Operator::Or,
+                    left,
+                    right,
+                } => Transformed::yes(Arc::new(Expr::BinaryOp {
+                    op: Operator::And,
+                    left: left.clone().not(),
+                    right: right.clone().not(),
+                })),
+                _ => Transformed::no(e),
+            },
+            _ => Transformed::no(e),
+        })
+    })
+    .unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use daft_dsl::col;
+
+    use crate::boolean::{to_cnf, to_dnf};
+
+    #[test]
+    fn dnf_simple() {
+        // a & (b | c) -> (a & b) | (a & c)
+        let expr = col("a").and(col("b").or(col("c")));
+        let expected = col("a").and(col("b")).or(col("a").and(col("c")));
+
+        assert_eq!(expected, to_dnf(expr));
+    }
+
+    #[test]
+    fn cnf_simple() {
+        // a | (b & c) -> (a | b) & (a | c)
+        let expr = col("a").or(col("b").and(col("c")));
+        let expected = col("a").or(col("b")).and(col("a").or(col("c")));
+
+        assert_eq!(expected, to_cnf(expr));
+    }
+
+    #[test]
+    fn dnf_nested() {
+        // a & b & ((c & d) | (e & f)) -> (a & b & c & d) | (a & b & e & f)
+        let expr = col("a")
+            .and(col("b"))
+            .and((col("c").and(col("d"))).or(col("e").and(col("f"))));
+        let expected = (col("a").and(col("b")).and(col("c").and(col("d"))))
+            .or(col("a").and(col("b")).and(col("e").and(col("f"))));
+
+        assert_eq!(expected, to_dnf(expr));
+    }
+
+    #[test]
+    fn cnf_nested() {
+        // a & b & ((c & d) | (e & f)) -> a & b & (c | e) & (c | f) & (d | e) & (d | f)
+        let expr = col("a")
+            .and(col("b"))
+            .and((col("c").and(col("d"))).or(col("e").and(col("f"))));
+        let expected = col("a").and(col("b")).and(
+            (col("c").or(col("e")))
+                .and(col("d").or(col("e")))
+                .and(col("c").or(col("f")).and(col("d").or(col("f")))),
+        );
+
+        assert_eq!(expected, to_cnf(expr));
+    }
+}

src/daft-logical-plan/src/optimization/rules/push_down_filter.rs

@@ -6,7 +6,7 @@ use std::{
 use common_error::DaftResult;
 use common_scan_info::{rewrite_predicate_for_partitioning, PredicateGroups};
 use common_treenode::{DynTreeNode, Transformed, TreeNode};
-use daft_algebra::boolean::{combine_conjunction, split_conjunction};
+use daft_algebra::boolean::{combine_conjunction, split_conjunction, to_cnf};
 use daft_core::join::JoinType;
 use daft_dsl::{
     col,
@@ -273,7 +273,8 @@ impl PushDownFilter {
                 let left_cols = HashSet::<_>::from_iter(child_join.left.schema().names());
                 let right_cols = HashSet::<_>::from_iter(child_join.right.schema().names());
 
-                for predicate in split_conjunction(&filter.predicate) {
+                // TODO: simplify predicates, since they may be expanded with `to_cnf`
+                for predicate in split_conjunction(&to_cnf(filter.predicate.clone())) {
                     let pred_cols = HashSet::<_>::from_iter(get_required_columns(&predicate));
 
                     match (
@@ -963,4 +964,61 @@ mod tests {
         assert_optimized_plan_eq(plan, expected)?;
         Ok(())
     }
+
+    /// Tests that a complex predicate can be separated so that it can be pushed down into one side of the join.
+    /// Modeled after TPC-H Q7
+    #[rstest]
+    fn filter_commutes_with_join_complex() -> DaftResult<()> {
+        let left_scan_op = dummy_scan_operator(vec![Field::new("a", DataType::Utf8)]);
+        let right_scan_op = dummy_scan_operator(vec![Field::new("b", DataType::Utf8)]);
+
+        let plan = dummy_scan_node(left_scan_op.clone())
+            .join(
+                dummy_scan_node(right_scan_op.clone()),
+                vec![],
+                vec![],
+                JoinType::Inner,
+                None,
+                None,
+                None,
+                false,
+            )?
+            .filter(
+                (col("a").eq(lit("FRANCE")).and(col("b").eq(lit("GERMANY"))))
+                    .or(col("a").eq(lit("GERMANY")).and(col("b").eq(lit("FRANCE")))),
+            )?
+            .build();
+
+        // let expected = left
+        let expected = dummy_scan_node_with_pushdowns(
+            left_scan_op,
+            Pushdowns::default().with_filters(Some(
+                col("a").eq(lit("FRANCE")).or(col("a").eq(lit("GERMANY"))),
+            )),
+        )
+        .join(
+            dummy_scan_node_with_pushdowns(
+                right_scan_op,
+                Pushdowns::default().with_filters(Some(
+                    col("b").eq(lit("GERMANY")).or(col("b").eq(lit("FRANCE"))),
+                )),
+            ),
+            vec![],
+            vec![],
+            JoinType::Inner,
+            None,
+            None,
+            None,
+            false,
+        )?
+        .filter(
+            (col("b").eq(lit("GERMANY")).or(col("a").eq(lit("GERMANY"))))
+                .and(col("a").eq(lit("FRANCE")).or(col("b").eq(lit("FRANCE")))),
+        )?
+        .build();
+
+        assert_optimized_plan_eq(plan, expected)?;
+
+        Ok(())
+    }
 }