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Introduce SortMergeReader (apache#12)
* Introduce SortMergeReader to perform a merge sort on the sorted reader list. * Fix several typos.
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...orage/src/main/java/org/apache/flink/table/storage/filestore/combine/SortMergeReader.java
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| /* | ||
| * 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. | ||
| */ | ||
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| package org.apache.flink.table.storage.filestore.combine; | ||
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| import org.apache.flink.table.data.RowData; | ||
| import org.apache.flink.table.storage.filestore.KeyValue; | ||
| import org.apache.flink.table.storage.filestore.utils.RecordIterator; | ||
| import org.apache.flink.table.storage.filestore.utils.RecordReader; | ||
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| import javax.annotation.Nullable; | ||
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| import java.io.IOException; | ||
| import java.util.Comparator; | ||
| import java.util.List; | ||
| import java.util.PriorityQueue; | ||
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| /** | ||
| * This reader is to read a list of {@link RecordReader}, which is already sorted by key and | ||
| * sequence number, and perform a sort merge algorithm. Note that values are not combined at this | ||
| * phase. | ||
| */ | ||
| public class SortMergeReader implements RecordReader<KeyValue> { | ||
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| private final List<RecordReader<KeyValue>> sortedReaders; | ||
| private final Comparator<RowData> userKeyComparator; | ||
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| private PriorityQueue<Element> minHeap; | ||
| private Element minElement; | ||
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| public SortMergeReader( | ||
| List<RecordReader<KeyValue>> sortedReaders, Comparator<RowData> userKeyComparator) { | ||
| this.sortedReaders = sortedReaders; | ||
| this.userKeyComparator = userKeyComparator; | ||
| } | ||
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| @Nullable | ||
| @Override | ||
| public RecordIterator<KeyValue> readBatch() throws IOException { | ||
| if (sortedReaders.isEmpty()) { | ||
| return null; | ||
| } | ||
| if (minHeap == null) { | ||
| initElements(); | ||
| } else { | ||
| supplyElements(); | ||
| } | ||
| if (minHeap.size() > 0) { | ||
| return new SortMergeIterator(); | ||
| } else { | ||
| return null; | ||
| } | ||
| } | ||
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| @Override | ||
| public void close() throws IOException { | ||
| for (RecordReader<KeyValue> reader : sortedReaders) { | ||
| reader.close(); | ||
| } | ||
| } | ||
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| private void initElements() throws IOException { | ||
| minHeap = | ||
| new PriorityQueue<>( | ||
| (e1, e2) -> { | ||
| int result = | ||
| userKeyComparator.compare( | ||
| e1.iterator.current().key(), | ||
| e2.iterator.current().key()); | ||
| if (result != 0) { | ||
| return result; | ||
| } | ||
| return Long.compare( | ||
| e1.iterator.current().sequenceNumber(), | ||
| e2.iterator.current().sequenceNumber()); | ||
| }); | ||
| for (int i = 0; i < sortedReaders.size(); i++) { | ||
| RecordIterator<KeyValue> iterator = sortedReaders.get(i).readBatch(); | ||
| if (iterator != null && iterator.advanceNext()) { | ||
| minHeap.offer(new Element(iterator, i)); | ||
| } | ||
| } | ||
| } | ||
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| private void supplyElements() throws IOException { | ||
| RecordReader<KeyValue> reader = sortedReaders.get(minElement.index); | ||
| RecordIterator<KeyValue> iterator = reader.readBatch(); | ||
| if (iterator != null && iterator.advanceNext()) { | ||
| minElement.iterator = iterator; | ||
| minHeap.offer(minElement); | ||
| } | ||
| } | ||
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| /** The iterator iterates on {@link SortMergeReader}. */ | ||
| private class SortMergeIterator implements RecordIterator<KeyValue> { | ||
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| private boolean justPeek = true; | ||
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| @Override | ||
| public boolean advanceNext() throws IOException { | ||
| if (minHeap.size() > 0) { | ||
| if (justPeek) { | ||
| // keep pace with the inner iterators | ||
| justPeek = false; | ||
| minElement = minHeap.peek(); | ||
| return true; | ||
| } | ||
| minElement = minHeap.poll(); | ||
| // find the top iterator to advance | ||
| RecordIterator<KeyValue> topIterator = minElement.iterator; | ||
| if (topIterator.advanceNext()) { | ||
| minHeap.offer(minElement); | ||
| minElement = minHeap.peek(); | ||
| return true; | ||
| } else { | ||
| // reach the end of current batch, should invoke the next batch | ||
| return false; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| @Override | ||
| public boolean singleInstance() { | ||
| return false; | ||
| } | ||
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| @Override | ||
| public KeyValue current() { | ||
| return minElement.iterator.current(); | ||
| } | ||
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| @Override | ||
| public void releaseBatch() {} | ||
| } | ||
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| /** | ||
| * A POJO class composed of a {@link RecordIterator} with the index in the input sorted readers. | ||
| * The index helps track which reader should invoke readBatch operation. | ||
| */ | ||
| private static class Element { | ||
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| private final int index; | ||
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| private RecordIterator<KeyValue> iterator; | ||
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| private Element(RecordIterator<KeyValue> iterator, int index) { | ||
| this.iterator = iterator; | ||
| this.index = index; | ||
| } | ||
| } | ||
| } |
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