SupportsFilterPushDown.java

/*
 * 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.table.connector.source.abilities;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.table.connector.source.ScanTableSource;
import org.apache.flink.table.expressions.ExpressionVisitor;
import org.apache.flink.table.expressions.ResolvedExpression;

import java.util.List;

/**
 * Enables to push down filters into a {@link ScanTableSource}.
 *
 * <p>Given the following SQL:
 *
 * <pre>{@code
 * SELECT * FROM t WHERE (a = '1' OR a = '2') AND b IS NOT NULL;
 * }</pre>
 *
 * <p>In the example above, {@code [a = '1' OR a = '2']} and {@code [b IS NOT NULL]} are acceptable
 * filters.
 *
 * <p>By default, if this interface is not implemented, filters are applied in a subsequent
 * operation after the source.
 *
 * <p>For efficiency, a source can push filters further down in order to be close to the actual data
 * generation. The passed filters are translated into conjunctive form. A source can pick filters
 * and return the accepted and remaining filters.
 *
 * <p>Accepted filters are filters that are consumed by the source but may be applied on a best
 * effort basis. The information about accepted filters helps the planner to adjust the cost
 * estimation for the current plan. A subsequent filter operation will still take place by the
 * runtime depending on the remaining filters.
 *
 * <p>Remaining filters are filters that cannot be fully applied by the source. The remaining
 * filters decide if a subsequent filter operation will still take place by the runtime.
 *
 * <p>By the above definition, accepted filters and remaining filters must not be disjunctive lists.
 * A filter can occur in both list. However, all given filters must be present in at least one list.
 *
 * <p>Note: A source is not allowed to change the given expressions in the returned {@link Result}.
 *
 * <p>Use {@link ExpressionVisitor} to traverse filter expressions.
 */
@PublicEvolving
public interface SupportsFilterPushDown {

    /**
     * Provides a list of filters in conjunctive form. A source can pick filters and return the
     * accepted and remaining filters.
     *
     * <p>See the documentation of {@link SupportsFilterPushDown} for more information.
     */
    Result applyFilters(List<ResolvedExpression> filters);

    /**
     * Result of a filter push down. It represents the communication of the source to the planner
     * during optimization.
     */
    @PublicEvolving
    final class Result {
        private final List<ResolvedExpression> acceptedFilters;
        private final List<ResolvedExpression> remainingFilters;

        private Result(
                List<ResolvedExpression> acceptedFilters,
                List<ResolvedExpression> remainingFilters) {
            this.acceptedFilters = acceptedFilters;
            this.remainingFilters = remainingFilters;
        }

        /**
         * Constructs a filter push-down result.
         *
         * <p>See the documentation of {@link SupportsFilterPushDown} for more information.
         *
         * @param acceptedFilters filters that are consumed by the source but may be applied on a
         *     best effort basis
         * @param remainingFilters filters that a subsequent filter operation still needs to perform
         *     during runtime
         */
        public static Result of(
                List<ResolvedExpression> acceptedFilters,
                List<ResolvedExpression> remainingFilters) {
            return new Result(acceptedFilters, remainingFilters);
        }

        public List<ResolvedExpression> getAcceptedFilters() {
            return acceptedFilters;
        }

        public List<ResolvedExpression> getRemainingFilters() {
            return remainingFilters;
        }
    }
}