AMashenkov commented on a change in pull request #9081: URL: https://github.com/apache/ignite/pull/9081#discussion_r645101172
########## File path: modules/core/src/main/java/org/apache/ignite/internal/processors/cache/query/MergeSortDistributedCacheQueryReducer.java ########## @@ -0,0 +1,290 @@ +/* + * 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.lang.reflect.Array; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Collection; +import java.util.Comparator; +import java.util.List; +import java.util.Map; +import java.util.NoSuchElementException; +import java.util.UUID; +import java.util.concurrent.ConcurrentHashMap; +import org.apache.ignite.IgniteCheckedException; +import org.apache.ignite.cluster.ClusterNode; +import org.apache.ignite.internal.util.typedef.internal.U; +import org.jetbrains.annotations.Nullable; + +/** + * Reducer of distirbuted query that sort result through all nodes. Note that it's assumed that every node + * returns pre-sorted collection of data. + */ +public class MergeSortDistributedCacheQueryReducer<R> extends UnsortedDistributedCacheQueryReducer<R> { + /** Map of Node ID to stream. Used for inserting new pages. */ + private final Map<UUID, NodePageStream> streamsMap; + + /** Array of streams. Used for iteration over result pages. */ + private final NodePageStream[] streams; + + /** If {@code true} then there wasn't call {@link #hasNext()} on this reducer. */ + private boolean first = true; + + /** + * Offset of current stream to get next value. This offset only increments if a stream is done. The array {@link + * #streams} is sorted to put stream with lowest value on this offset. + */ + private int streamOff; + + /** Compares head of streams to get lowest value at the moment. */ + private final Comparator<NodePageStream> streamCmp; + + /** + * @param rowCmp Comparator to sort query results from different nodes. + */ + public MergeSortDistributedCacheQueryReducer(GridCacheQueryFutureAdapter fut, long reqId, + CacheQueryPageRequester fetcher, Collection<ClusterNode> nodes, Comparator<R> rowCmp + ) { + super(fut, reqId, fetcher, nodes); + + streamsMap = new ConcurrentHashMap<>(nodes.size()); + streams = (NodePageStream[])Array.newInstance(NodePageStream.class, nodes.size()); + + int i = 0; + + for (ClusterNode node : nodes) { + streams[i] = new NodePageStream(node.id()); + streamsMap.put(node.id(), streams[i++]); + } + + streamCmp = (o1, o2) -> { + if (o1 == o2) + return 0; + + if (o1 == null) + return -1; + + if (o2 == null) + return 1; + + return rowCmp.compare(o1.head, o2.head); + }; + } + + /** {@inheritDoc} */ + @Override public R next() throws IgniteCheckedException { + for (int i = streamOff; i < streams.length; i++) { + NodePageStream s = streams[i]; + + // Skip if stream has head: on previous next() head extracts from stream[streamOff], others streams do + // have head or it is the first run. + if (s.head() != null) + break; + + if (!s.hasNext()) { + // Nullify obsolete stream, move left bound. + streamsMap.remove(s.nodeId); + streams[i] = null; + streamOff++; + } + else { + // Prefetch head value. + s.next(); + } + } + + if (finished()) + throw new NoSuchElementException("No next element. Please, be sure to invoke hasNext() before next()."); + + if (first) { + first = false; + + Arrays.sort(streams, streamCmp); + } else + bubbleUp(streams, streamOff, streamCmp); + + return streams[streamOff].get(); + } + + /** {@inheritDoc} */ + @Override public boolean hasNext() throws IgniteCheckedException { + for (int i = streamOff; i < streams.length; i++) { + if (streams[i].hasNext()) + return true; + + // Nullify obsolete stream, move left bound. + streamsMap.remove(streams[i].nodeId); + streams[i] = null; + streamOff++; + } + + return false; + } + + /** {@inheritDoc} */ + @Override protected void loadPage() { + assert !Thread.holdsLock(queueLock()); + + List<UUID> nodes; + + synchronized (queueLock()) { Review comment: You use the same lock to synchronize access to streams[] and all queues in all NodeStrems objects. What is the purpose to use a shared lock? -- This is an automated message from the Apache Git Service. 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