Make PruningPredicate's rewrite public

Author: adriangb

datafusion/core/src/physical_optimizer/pruning.rs

@@ -478,6 +478,37 @@ pub struct PruningPredicate {
     literal_guarantees: Vec<LiteralGuarantee>,
 }
 
+/// Hook to handle predicates that DataFusion can not handle, e.g. certain complex expressions
+/// or predicates that reference columns that are not in the schema.
+pub trait UnhandledPredicateHook {
+    /// Called when a predicate can not be handled by DataFusion's transformation rules
+    /// or is referencing a column that is not in the schema.
+    fn handle(&self, expr: &Arc<dyn PhysicalExpr>) -> Arc<dyn PhysicalExpr>;
+}
+
+#[derive(Debug, Clone)]
+struct ConstantUnhandledPredicateHook {
+    default: Arc<dyn PhysicalExpr>,
+}
+
+impl ConstantUnhandledPredicateHook {
+    fn new(default: Arc<dyn PhysicalExpr>) -> Self {
+        Self { default }
+    }
+}
+
+impl UnhandledPredicateHook for ConstantUnhandledPredicateHook {
+    fn handle(&self, _expr: &Arc<dyn PhysicalExpr>) -> Arc<dyn PhysicalExpr> {
+        self.default.clone()
+    }
+}
+
+fn default_unhandled_hook() -> Arc<dyn UnhandledPredicateHook> {
+    Arc::new(ConstantUnhandledPredicateHook::new(Arc::new(
+        phys_expr::Literal::new(ScalarValue::Boolean(Some(true))),
+    )))
+}
+
 impl PruningPredicate {
     /// Try to create a new instance of [`PruningPredicate`]
     ///
@@ -502,10 +533,16 @@ impl PruningPredicate {
     /// See the struct level documentation on [`PruningPredicate`] for more
     /// details.
     pub fn try_new(expr: Arc<dyn PhysicalExpr>, schema: SchemaRef) -> Result<Self> {
+        let unhandled_hook = default_unhandled_hook();
+
         // build predicate expression once
         let mut required_columns = RequiredColumns::new();
-        let predicate_expr =
-            build_predicate_expression(&expr, schema.as_ref(), &mut required_columns);
+        let predicate_expr = build_predicate_expression(
+            &expr,
+            schema.as_ref(),
+            &mut required_columns,
+            &unhandled_hook,
+        );
 
         let literal_guarantees = LiteralGuarantee::analyze(&expr);
 
@@ -1316,23 +1353,43 @@ const MAX_LIST_VALUE_SIZE_REWRITE: usize = 20;
 /// expression that will evaluate to FALSE if it can be determined no
 /// rows between the min/max values could pass the predicates.
 ///
+/// Any predicates that can not be translated will be passed to `unhandled_hook`.
+///
 /// Returns the pruning predicate as an [`PhysicalExpr`]
 ///
-/// Notice: Does not handle [`phys_expr::InListExpr`] greater than 20, which will be rewritten to TRUE
+/// Notice: Does not handle [`phys_expr::InListExpr`] greater than 20, which will fall back to calling `unhandled_hook`
+pub fn rewrite_predicate_to_statistics_predicate(
+    expr: &Arc<dyn PhysicalExpr>,
+    schema: &Schema,
+    unhandled_hook: Option<Arc<dyn UnhandledPredicateHook>>,
+) -> Arc<dyn PhysicalExpr> {
+    let unhandled_hook = unhandled_hook.unwrap_or(default_unhandled_hook());
+
+    let mut required_columns = RequiredColumns::new();
+
+    build_predicate_expression(expr, schema, &mut required_columns, &unhandled_hook)
+}
+
+/// Translate logical filter expression into pruning predicate
+/// expression that will evaluate to FALSE if it can be determined no
+/// rows between the min/max values could pass the predicates.
+///
+/// Any predicates that can not be translated will be passed to `unhandled_hook`.
+///
+/// Returns the pruning predicate as an [`PhysicalExpr`]
+///
+/// Notice: Does not handle [`phys_expr::InListExpr`] greater than 20, which will fall back to calling `unhandled_hook`
 fn build_predicate_expression(
     expr: &Arc<dyn PhysicalExpr>,
     schema: &Schema,
     required_columns: &mut RequiredColumns,
+    unhandled_hook: &Arc<dyn UnhandledPredicateHook>,
 ) -> Arc<dyn PhysicalExpr> {
-    // Returned for unsupported expressions. Such expressions are
-    // converted to TRUE.
-    let unhandled = Arc::new(phys_expr::Literal::new(ScalarValue::Boolean(Some(true))));
-
     // predicate expression can only be a binary expression
     let expr_any = expr.as_any();
     if let Some(is_null) = expr_any.downcast_ref::<phys_expr::IsNullExpr>() {
         return build_is_null_column_expr(is_null.arg(), schema, required_columns, false)
-            .unwrap_or(unhandled);
+            .unwrap_or_else(|| unhandled_hook.handle(expr));
     }
     if let Some(is_not_null) = expr_any.downcast_ref::<phys_expr::IsNotNullExpr>() {
         return build_is_null_column_expr(
@@ -1341,19 +1398,19 @@ fn build_predicate_expression(
             required_columns,
             true,
         )
-        .unwrap_or(unhandled);
+        .unwrap_or_else(|| unhandled_hook.handle(expr));
     }
     if let Some(col) = expr_any.downcast_ref::<phys_expr::Column>() {
         return build_single_column_expr(col, schema, required_columns, false)
-            .unwrap_or(unhandled);
+            .unwrap_or_else(|| unhandled_hook.handle(expr));
     }
     if let Some(not) = expr_any.downcast_ref::<phys_expr::NotExpr>() {
         // match !col (don't do so recursively)
         if let Some(col) = not.arg().as_any().downcast_ref::<phys_expr::Column>() {
             return build_single_column_expr(col, schema, required_columns, true)
-                .unwrap_or(unhandled);
+                .unwrap_or_else(|| unhandled_hook.handle(expr));
         } else {
-            return unhandled;
+            return unhandled_hook.handle(expr);
         }
     }
     if let Some(in_list) = expr_any.downcast_ref::<phys_expr::InListExpr>() {
@@ -1382,9 +1439,14 @@ fn build_predicate_expression(
                 })
                 .reduce(|a, b| Arc::new(phys_expr::BinaryExpr::new(a, re_op, b)) as _)
                 .unwrap();
-            return build_predicate_expression(&change_expr, schema, required_columns);
+            return build_predicate_expression(
+                &change_expr,
+                schema,
+                required_columns,
+                unhandled_hook,
+            );
         } else {
-            return unhandled;
+            return unhandled_hook.handle(expr);
         }
     }
 
@@ -1396,21 +1458,23 @@ fn build_predicate_expression(
                 bin_expr.right().clone(),
             )
         } else {
-            return unhandled;
+            return unhandled_hook.handle(expr);
         }
     };
 
     if op == Operator::And || op == Operator::Or {
-        let left_expr = build_predicate_expression(&left, schema, required_columns);
-        let right_expr = build_predicate_expression(&right, schema, required_columns);
+        let left_expr =
+            build_predicate_expression(&left, schema, required_columns, unhandled_hook);
+        let right_expr =
+            build_predicate_expression(&right, schema, required_columns, unhandled_hook);
         // simplify boolean expression if applicable
         let expr = match (&left_expr, op, &right_expr) {
             (left, Operator::And, _) if is_always_true(left) => right_expr,
             (_, Operator::And, right) if is_always_true(right) => left_expr,
             (left, Operator::Or, right)
                 if is_always_true(left) || is_always_true(right) =>
             {
-                unhandled
+                Arc::new(phys_expr::Literal::new(ScalarValue::Boolean(Some(true))))
             }
             _ => Arc::new(phys_expr::BinaryExpr::new(left_expr, op, right_expr)),
         };
@@ -1423,12 +1487,11 @@ fn build_predicate_expression(
         Ok(builder) => builder,
         // allow partial failure in predicate expression generation
         // this can still produce a useful predicate when multiple conditions are joined using AND
-        Err(_) => {
-            return unhandled;
-        }
+        Err(_) => return unhandled_hook.handle(expr),
     };
 
-    build_statistics_expr(&mut expr_builder).unwrap_or(unhandled)
+    build_statistics_expr(&mut expr_builder)
+        .unwrap_or_else(|_| unhandled_hook.handle(expr))
 }
 
 fn build_statistics_expr(
@@ -1582,6 +1645,8 @@ mod tests {
     use arrow_array::UInt64Array;
     use datafusion_expr::expr::InList;
     use datafusion_expr::{cast, is_null, try_cast, Expr};
+    use datafusion_functions_nested::expr_fn::{array_has, make_array};
+    use datafusion_physical_expr::expressions as phys_expr;
     use datafusion_physical_expr::planner::logical2physical;
 
     #[derive(Debug, Default)]
@@ -3397,6 +3462,75 @@ mod tests {
         // TODO: add test for other case and op
     }
 
+    #[test]
+    fn test_rewrite_expr_to_prunable_custom_unhandled_hook() {
+        struct CustomUnhandledHook;
+
+        impl UnhandledPredicateHook for CustomUnhandledHook {
+            /// This handles an arbitrary case of a column that doesn't exist in the schema
+            /// by renaming it to yet another column that doesn't exist in the schema
+            /// (the transformation is arbitrary, the point is that it can do whatever it wants)
+            fn handle(&self, _expr: &Arc<dyn PhysicalExpr>) -> Arc<dyn PhysicalExpr> {
+                Arc::new(phys_expr::Literal::new(ScalarValue::Int32(Some(42))))
+            }
+        }
+
+        let schema = Schema::new(vec![Field::new("a", DataType::Int32, true)]);
+        let schema_with_b = Schema::new(vec![
+            Field::new("a", DataType::Int32, true),
+            Field::new("b", DataType::Int32, true),
+        ]);
+
+        let transform_expr = |expr| {
+            let expr = logical2physical(&expr, &schema_with_b);
+            rewrite_predicate_to_statistics_predicate(
+                &expr,
+                &schema,
+                Some(Arc::new(CustomUnhandledHook {})),
+            )
+        };
+
+        // transform an arbitrary valid expression that we know is handled
+        let known_expression = col("a").eq(lit(ScalarValue::Int32(Some(12))));
+        let known_expression_transformed = rewrite_predicate_to_statistics_predicate(
+            &logical2physical(&known_expression, &schema),
+            &schema,
+            None,
+        );
+
+        // an expression referencing an unknown column (that is not in the schema) gets passed to the hook
+        let input = col("b").eq(lit(ScalarValue::Int32(Some(12))));
+        let expected = logical2physical(&lit(42), &schema);
+        let transformed = transform_expr(input.clone());
+        assert_eq!(transformed.to_string(), expected.to_string());
+
+        // more complex case with unknown column
+        let input = known_expression.clone().and(input.clone());
+        let expected = phys_expr::BinaryExpr::new(
+            known_expression_transformed.clone(),
+            Operator::And,
+            logical2physical(&lit(42), &schema),
+        );
+        let transformed = transform_expr(input.clone());
+        assert_eq!(transformed.to_string(), expected.to_string());
+
+        // an unknown expression gets passed to the hook
+        let input = array_has(make_array(vec![lit(1)]), col("a"));
+        let expected = logical2physical(&lit(42), &schema);
+        let transformed = transform_expr(input.clone());
+        assert_eq!(transformed.to_string(), expected.to_string());
+
+        // more complex case with unknown expression
+        let input = known_expression.and(input);
+        let expected = phys_expr::BinaryExpr::new(
+            known_expression_transformed.clone(),
+            Operator::And,
+            logical2physical(&lit(42), &schema),
+        );
+        let transformed = transform_expr(input.clone());
+        assert_eq!(transformed.to_string(), expected.to_string());
+    }
+
     #[test]
     fn test_rewrite_expr_to_prunable_error() {
         // cast string value to numeric value
@@ -3886,6 +4020,7 @@ mod tests {
         required_columns: &mut RequiredColumns,
     ) -> Arc<dyn PhysicalExpr> {
         let expr = logical2physical(expr, schema);
-        build_predicate_expression(&expr, schema, required_columns)
+        let unhandled_hook = default_unhandled_hook();
+        build_predicate_expression(&expr, schema, required_columns, &unhandled_hook)
     }
 }