/*
* 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.
*/
package org.apache.flink.streaming.api.operators;
import org.apache.flink.annotation.PublicEvolving;
/**
* Defines the chaining scheme for the operator. When an operator is chained to the
* predecessor, it means that they run in the same thread. They become one operator
* consisting of multiple steps.
*
* <p>The default value used by the {@link StreamOperator} is {@link #HEAD}, which means that
* the operator is not chained to its predecessor. Most operators override this with
* {@link #ALWAYS}, meaning they will be chained to predecessors whenever possible.
*/
@PublicEvolving
public enum ChainingStrategy {
/**
* Operators will be eagerly chained whenever possible.
*
* <p>To optimize performance, it is generally a good practice to allow maximal
* chaining and increase operator parallelism.
*/
ALWAYS,
/**
* The operator will not be chained to the preceding or succeeding operators.
*/
NEVER,
/**
* The operator will not be chained to the predecessor, but successors may chain to this
* operator.
*/
HEAD
}