AMashenkov commented on a change in pull request #9081: URL: https://github.com/apache/ignite/pull/9081#discussion_r645145710
########## File path: modules/core/src/main/java/org/apache/ignite/internal/processors/cache/query/CacheQueryReducer.java ########## @@ -0,0 +1,58 @@ +/* + * 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.ignite.internal.processors.cache.query; + +import java.util.Collection; +import java.util.UUID; +import org.apache.ignite.IgniteCheckedException; +import org.jetbrains.annotations.Nullable; + +/** + * This class is responsible for reducing results of cache query. Query results are delivered with function + * {@link #addPage(UUID, Collection)}. Note that this reducer deeply interacts with corresponding query future + * {@link GridCacheQueryFutureAdapter}, so they used the same lock object. It guards reducer pages operations + * and the future status. Custom reduce logic is applied within {@link #next()} and {@link #hasNext()}. + * + * <T> is a type of cache query result item. + */ +public interface CacheQueryReducer<T> { + /** + * @return Next item. + */ + public T next() throws IgniteCheckedException; + + /** + * @return {@code true} if there is a next item, otherwise {@code false}. + */ + public boolean hasNext() throws IgniteCheckedException; + + /** + * Offer query result page for reduce. Note that the data collection may contain extension of type T. + * In such cases it stores additional payload for custom reducer logic. + * + * @param nodeId Node ID that sent this page. {@code null} means local node or error page. + * @param data Page data rows. + */ + public void addPage(@Nullable UUID nodeId, Collection<T> data); + + /** + * Callback that invokes after reducer get last query result page. + * Also invokes for failed queries to let reducer know that there won't be new pages. Review comment: Why there is no onCancel() or onError() callbacks that will cause Exception throwing in `next` method? -- 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. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
