org.apache.hadoop.dynamodb.preader.ScanReadManager Maven / Gradle / Ivy

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/**
 * Copyright 2012-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file
 * except in compliance with the License. A copy of the License is located at
 *
 *     http://aws.amazon.com/apache2.0/
 *
 * or in the "LICENSE.TXT" file accompanying this file. This file 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.hadoop.dynamodb.preader;

import org.apache.hadoop.dynamodb.util.AbstractTimeSource;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class ScanReadManager extends AbstractReadManager {

  public ScanReadManager(RateController rateController, AbstractTimeSource time,
      DynamoDBRecordReaderContext context) {
    super(rateController, time, context);
  }

  @Override
  protected void initializeReadRequests() {
    // Create a temporary copy of the segments, as we're about to shuffle it
    List shuffleSgments = new ArrayList<>(context.getSplit().getSegments());
    if (shuffleSgments.isEmpty()) {
      String errorMsg = "0 segment. Need at least one segment to work with.";
      log.error(errorMsg);
      throw new RuntimeException(errorMsg);
    }

    // Shuffle the segments.
    Collections.shuffle(shuffleSgments, new Random());

    // Keep track of how many segments remain to be scanned. Used by the
    // record readers to signal completion once all segments have been fully
    // scanned.
    segmentsRemaining.set(shuffleSgments.size());

    // Queue up segment scan requests
    for (Integer segment : shuffleSgments) {
      enqueueReadRequestToTail(new ScanRecordReadRequest(this, context, segment, null /*
      lastEvaluatedKey */));
    }
  }
}