alamb commented on code in PR #5623:
URL: https://github.com/apache/arrow-datafusion/pull/5623#discussion_r1141036350
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datafusion/optimizer/src/optimizer.rs:
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@@ -419,6 +412,34 @@ impl Optimizer {
}
}
+/// Returns an error if plans have different schemas.
Review Comment:
This is a nice refactor
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datafusion/optimizer/src/plan_signature.rs:
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@@ -0,0 +1,132 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::{
+ collections::hash_map::DefaultHasher,
+ convert::Infallible,
+ hash::{Hash, Hasher},
+ num::NonZeroUsize,
+};
+
+use datafusion_expr::{LogicalPlan, PlanVisitor};
+
+/// Non-unique identifier of a [`LogicalPlan`].
+///
+/// See [`LogicalPlanSignature::compute`] for details.
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+pub struct LogicalPlanSignature {
+ node_number: NonZeroUsize,
+ plan_hash: u64,
+}
+
+impl LogicalPlanSignature {
+ /// Returns [`LogicalPlanSignature`] of the given [`LogicalPlan`].
+ ///
+ /// It is a kind of [`LogicalPlan`] hashing with stronger guarantees.
+ ///
+ /// # Guarantees
+ ///
+ /// Consider two [`LogicalPlan`]s `p1` and `p2`.
+ ///
+ /// If `p1` and `p2` have a different number of [`LogicalPlan`]s, then
+ /// they will have different [`LogicalPlanSignature`]s.
+ ///
+ /// If `p1` and `p2` have a different [`Hash`], then
+ /// they will have different [`LogicalPlanSignature`]s.
+ ///
+ /// # Caveats
+ ///
+ /// The intention of [`LogicalPlanSignature`] is to have a lower chance
+ /// of hash collisions.
+ ///
+ /// There exist different [`LogicalPlan`]s with the same
+ /// [`LogicalPlanSignature`].
+ ///
+ /// When two [`LogicalPlan`]s differ only in metadata, then they will have
+ /// the same [`LogicalPlanSignature`]s (due to hash implementation in
+ /// [`LogicalPlan`]).
+ pub fn compute(plan: &LogicalPlan) -> Self {
Review Comment:
I think `pub fn new()` would be more idiomatic to construct a new plan
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