[GitHub] [arrow-datafusion] houqp commented on a change in pull request #965: Move CBOs and Statistics to physical plan

[GitBox <gi...@apache.org>]

houqp commented on a change in pull request #965:
URL: https://github.com/apache/arrow-datafusion/pull/965#discussion_r706882220



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File path: datafusion/src/physical_optimizer/aggregate_statistics.rs
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@@ -0,0 +1,384 @@
+// 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.
+
+//! Utilizing exact statistics from sources to avoid scanning data
+use std::sync::Arc;
+
+use arrow::datatypes::Schema;

Review comment:
       The code is indeed more complex than the logical optimizer. I feel like moving CBO into physical plane is the right move from a design's point of view. The vtable is hard to avoid because we want to make it extensible by 3rd party plugins.
   
   So perhaps what we can do as a follow up of this PR is to come up with better helper function/macro to make it more readable and maintainable. @Dandandan 's https://github.com/apache/arrow-datafusion/pull/441 and @alamb 's `ExprRewriter` are good examples of such constructs.




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