| /* |
| * 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.druid.query.aggregation; |
| |
| import org.apache.druid.guice.annotations.ExtensionPoint; |
| import org.apache.druid.query.monomorphicprocessing.RuntimeShapeInspector; |
| import org.apache.druid.segment.ColumnValueSelector; |
| |
| /** |
| * AggregateCombiner is used to fold rollup aggregation results from serveral "rows" of different indexes during index |
| * merging (see {@link org.apache.druid.segment.IndexMerger}). |
| * |
| * The state of the implementations of this interface is an aggregation value (either a primitive or an object), that |
| * could be queried via {@link ColumnValueSelector}'s methods. Before {@link #reset} is ever called on an |
| * AggregateCombiner, it's state is undefined and {@link ColumnValueSelector}'s methods could return something random, |
| * or null, or throw an exception. |
| * |
| * This interface would probably better be called "AggregateFolder", but somebody may confuse it with "folder" as |
| * "directory" synonym. |
| * |
| * @see AggregatorFactory#makeAggregateCombiner() |
| * @see LongAggregateCombiner |
| * @see DoubleAggregateCombiner |
| * @see ObjectAggregateCombiner |
| */ |
| @ExtensionPoint |
| public interface AggregateCombiner<T> extends ColumnValueSelector<T> |
| { |
| /** |
| * Resets this AggregateCombiner's state value to the value of the given selector, e. g. after calling this method |
| * combiner.get*() should return the same value as selector.get*(). |
| * |
| * If the selector is an {@link org.apache.druid.segment.ObjectColumnSelector}, the object returned from {@link |
| * org.apache.druid.segment.ObjectColumnSelector#getObject()} must not be modified, and must not become a subject for |
| * modification during subsequent {@link #fold} calls. |
| */ |
| void reset(ColumnValueSelector selector); |
| |
| /** |
| * Folds this AggregateCombiner's state value with the value of the given selector and saves it in this |
| * AggregateCombiner's state, e. g. after calling combiner.fold(selector), combiner.get*() should return the value |
| * that would be the result of {@link AggregatorFactory#combine |
| * aggregatorFactory.combine(combiner.get*(), selector.get*())} call. |
| * |
| * Unlike {@link AggregatorFactory#combine}, if the selector is an {@link org.apache.druid.segment.ObjectColumnSelector}, the |
| * object returned from {@link org.apache.druid.segment.ObjectColumnSelector#getObject()} must not be modified, and must not |
| * become a subject for modification during subsequent fold() calls. |
| * |
| * Since the state of AggregateCombiner is undefined before {@link #reset} is ever called on it, the effects of |
| * calling fold() are also undefined in this case. |
| * |
| * @see AggregatorFactory#combine |
| */ |
| void fold(ColumnValueSelector selector); |
| |
| @Override |
| default boolean isNull() |
| { |
| return false; |
| } |
| |
| @Override |
| default void inspectRuntimeShape(RuntimeShapeInspector inspector) |
| { |
| // Usually AggregateCombiners have nothing to inspect, because their getLong/getDouble/getFloat (the methods |
| // annotated @CalledFromHotLoop in AggregateCombiner) is a plain getter of a field, so there is no source for |
| // branching and otherwise non-monomorphic runtime profile. |
| } |
| } |