adriangb commented on code in PR #20065: URL: https://github.com/apache/datafusion/pull/20065#discussion_r2749748658
########## datafusion/expr-common/src/placement.rs: ########## @@ -0,0 +1,59 @@ +// 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. + +//! Expression placement information for optimization decisions. + +/// Describes where an expression should be placed in the query plan for +/// optimal execution. This is used by optimizers to make decisions about +/// expression placement, such as whether to push expressions down through +/// projections. +#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)] +pub enum ExpressionPlacement { + /// A constant literal value. + Literal, + /// A simple column reference. + Column, + /// A cheap expression that can be pushed to leaf nodes in the plan. + /// Examples include `get_field` for struct field access. + PlaceAtLeaves, + /// An expensive expression that should stay at the root of the plan. + /// This is the default for most expressions. + PlaceAtRoot, Review Comment: The other thing I wonder is if `PlaceAtRoot` should be `NeutralPlacement` or similar as we don't currently do any effort to hoist expressions up towards the root. We were [just discussing](https://discord.com/channels/885562378132000778/1466445692187840678) with @jackkleeman about moving expensive UDFs up the tree. While I don't want to implement the optimizer rule, etc. in this PR I do think it's related so maybe we should name the enums to allow for later introducing a variant that lets expressions declare "I am so expensive that I should be moved as far up the tree as possible"? Thoughts @jackkleeman? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
