hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockIdManager.java

/**
 * 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.hadoop.hdfs.server.blockmanagement;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import org.apache.hadoop.hdfs.protocol.Block;
import org.apache.hadoop.hdfs.protocol.HdfsConstants;
import org.apache.hadoop.hdfs.server.common.GenerationStamp;
import org.apache.hadoop.hdfs.server.common.HdfsServerConstants;

import java.io.IOException;

/**
 * BlockIdManager allocates the generation stamps and the block ID. The
 * {@see FSNamesystem} is responsible for persisting the allocations in the
 * {@see EditLog}.
 */
public class BlockIdManager {
  /**
   * The global generation stamp for legacy blocks with randomly
   * generated block IDs.
   */
  private final GenerationStamp legacyGenerationStamp = new GenerationStamp();
  /**
   * The global generation stamp for this file system.
   */
  private final GenerationStamp generationStamp = new GenerationStamp();
  /**
   * Most recent global generation stamp as seen on Active NameNode.
   * Used by StandbyNode only.<p/>
   * StandbyNode does not update its global {@link #generationStamp} during
   * edits tailing. The global generation stamp on StandbyNode is updated
   * <ol><li>when the block with the next generation stamp is actually
   * received</li>
   * <li>during fail-over it is bumped to the last value received from the
   * Active NN through edits and stored as
   * {@link #impendingGenerationStamp}</li></ol>
   * The former helps to avoid a race condition with IBRs during edits tailing.
   * The latter guarantees that generation stamps are never reused by new
   * Active after fail-over.
   * <p/> See HDFS-14941 for more details.
   */
  private final GenerationStamp impendingGenerationStamp
      = new GenerationStamp();
  /**
   * The value of the generation stamp when the first switch to sequential
   * block IDs was made. Blocks with generation stamps below this value
   * have randomly allocated block IDs. Blocks with generation stamps above
   * this value had sequentially allocated block IDs. Read from the fsImage
   * (or initialized as an offset from the V1 (legacy) generation stamp on
   * upgrade).
   */
  private long legacyGenerationStampLimit;
  /**
   * The global block ID space for this file system.
   */
  private final SequentialBlockIdGenerator blockIdGenerator;

  public BlockIdManager(BlockManager blockManager) {
    this.legacyGenerationStampLimit =
        HdfsConstants.GRANDFATHER_GENERATION_STAMP;
    this.blockIdGenerator = new SequentialBlockIdGenerator(blockManager);
  }

  /**
   * Upgrades the generation stamp for the filesystem
   * by reserving a sufficient range for all existing blocks.
   * Should be invoked only during the first upgrade to
   * sequential block IDs.
   */
  public long upgradeLegacyGenerationStamp() {
    Preconditions.checkState(generationStamp.getCurrentValue() ==
      GenerationStamp.LAST_RESERVED_STAMP);
    generationStamp.skipTo(legacyGenerationStamp.getCurrentValue() +
      HdfsServerConstants.RESERVED_LEGACY_GENERATION_STAMPS);

    legacyGenerationStampLimit = generationStamp.getCurrentValue();
    return generationStamp.getCurrentValue();
  }

  /**
   * Sets the generation stamp that delineates random and sequentially
   * allocated block IDs.
   *
   * @param stamp set generation stamp limit to this value
   */
  public void setLegacyGenerationStampLimit(long stamp) {
    Preconditions.checkState(legacyGenerationStampLimit ==
        HdfsConstants.GRANDFATHER_GENERATION_STAMP);
    legacyGenerationStampLimit = stamp;
  }

  /**
   * Gets the value of the generation stamp that delineates sequential
   * and random block IDs.
   */
  public long getGenerationStampAtblockIdSwitch() {
    return legacyGenerationStampLimit;
  }

  @VisibleForTesting
  SequentialBlockIdGenerator getBlockIdGenerator() {
    return blockIdGenerator;
  }

  /**
   * Sets the maximum allocated block ID for this filesystem. This is
   * the basis for allocating new block IDs.
   */
  public void setLastAllocatedBlockId(long blockId) {
    blockIdGenerator.skipTo(blockId);
  }

  /**
   * Gets the maximum sequentially allocated block ID for this filesystem
   */
  public long getLastAllocatedBlockId() {
    return blockIdGenerator.getCurrentValue();
  }

  /**
   * Sets the current generation stamp for legacy blocks
   */
  public void setLegacyGenerationStamp(long stamp) {
    legacyGenerationStamp.setCurrentValue(stamp);
  }

  /**
   * Gets the current generation stamp for legacy blocks
   */
  public long getLegacyGenerationStamp() {
    return legacyGenerationStamp.getCurrentValue();
  }

  /**
   * Gets the current generation stamp for this filesystem
   */
  public void setGenerationStamp(long stamp) {
    generationStamp.setCurrentValue(stamp);
  }

  /**
   * Set the currently highest gen stamp from active. Used
   * by Standby only.
   * @param stamp new genstamp
   */
  public void setImpendingGenerationStamp(long stamp) {
    impendingGenerationStamp.setIfGreater(stamp);
  }

  /**
   * Set the current genstamp to the impending genstamp.
   */
  public void applyImpendingGenerationStamp() {
    setGenerationStampIfGreater(impendingGenerationStamp.getCurrentValue());
  }

  @VisibleForTesting
  public long getImpendingGenerationStamp() {
    return impendingGenerationStamp.getCurrentValue();
  }

  /**
   * Set genstamp only when the given one is higher.
   * @param stamp
   */
  public void setGenerationStampIfGreater(long stamp) {
    generationStamp.setIfGreater(stamp);
  }

  public long getGenerationStamp() {
    return generationStamp.getCurrentValue();
  }

  /**
   * Increments, logs and then returns the stamp
   */
  long nextGenerationStamp(boolean legacyBlock) throws IOException {
    return legacyBlock ? getNextLegacyGenerationStamp() :
        getNextGenerationStamp();
  }

  @VisibleForTesting
  long getNextLegacyGenerationStamp() throws IOException {
    long legacyGenStamp = legacyGenerationStamp.nextValue();

    if (legacyGenStamp >= legacyGenerationStampLimit) {
      // We ran out of generation stamps for legacy blocks. In practice, it
      // is extremely unlikely as we reserved 1T legacy generation stamps. The
      // result is that we can no longer append to the legacy blocks that
      // were created before the upgrade to sequential block IDs.
      throw new OutOfLegacyGenerationStampsException();
    }

    return legacyGenStamp;
  }

  @VisibleForTesting
  long getNextGenerationStamp() {
    return generationStamp.nextValue();
  }

  public long getLegacyGenerationStampLimit() {
    return legacyGenerationStampLimit;
  }

  /**
   * Determine whether the block ID was randomly generated (legacy) or
   * sequentially generated. The generation stamp value is used to
   * make the distinction.
   *
   * @return true if the block ID was randomly generated, false otherwise.
   */
  boolean isLegacyBlock(Block block) {
    return block.getGenerationStamp() < getLegacyGenerationStampLimit();
  }

  /**
   * Increments, logs and then returns the block ID
   */
  long nextBlockId() {
    return blockIdGenerator.nextValue();
  }

  boolean isGenStampInFuture(Block block) {
    if (isLegacyBlock(block)) {
      return block.getGenerationStamp() > getLegacyGenerationStamp();
    } else {
      return block.getGenerationStamp() > getGenerationStamp();
    }
  }

  void clear() {
    legacyGenerationStamp.setCurrentValue(GenerationStamp.LAST_RESERVED_STAMP);
    generationStamp.setCurrentValue(GenerationStamp.LAST_RESERVED_STAMP);
    getBlockIdGenerator().setCurrentValue(SequentialBlockIdGenerator
      .LAST_RESERVED_BLOCK_ID);
    legacyGenerationStampLimit = HdfsConstants.GRANDFATHER_GENERATION_STAMP;
  }
}