hbase-server/src/main/java/org/apache/hadoop/hbase/wal/EntryBuffers.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.hbase.wal;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;

import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.io.HeapSize;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.ClassSize;
import org.apache.hadoop.hbase.wal.WALSplitter.PipelineController;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Class which accumulates edits and separates them into a buffer per region while simultaneously
 * accounting RAM usage. Blocks if the RAM usage crosses a predefined threshold. Writer threads then
 * pull region-specific buffers from this class.
 */
@InterfaceAudience.Private
class EntryBuffers {
  private static final Logger LOG = LoggerFactory.getLogger(EntryBuffers.class);

  private final PipelineController controller;

  final Map<byte[], RegionEntryBuffer> buffers = new TreeMap<>(Bytes.BYTES_COMPARATOR);

  /*
   * Track which regions are currently in the middle of writing. We don't allow an IO thread to pick
   * up bytes from a region if we're already writing data for that region in a different IO thread.
   */
  private final Set<byte[]> currentlyWriting = new TreeSet<>(Bytes.BYTES_COMPARATOR);

  protected long totalBuffered = 0;
  protected final long maxHeapUsage;

  public EntryBuffers(PipelineController controller, long maxHeapUsage) {
    this.controller = controller;
    this.maxHeapUsage = maxHeapUsage;
  }

  /**
   * Append a log entry into the corresponding region buffer. Blocks if the total heap usage has
   * crossed the specified threshold.
   */
  void appendEntry(WAL.Entry entry) throws InterruptedException, IOException {
    WALKey key = entry.getKey();
    RegionEntryBuffer buffer;
    long incrHeap;
    synchronized (this) {
      buffer = buffers.get(key.getEncodedRegionName());
      if (buffer == null) {
        buffer = new RegionEntryBuffer(key.getTableName(), key.getEncodedRegionName());
        buffers.put(key.getEncodedRegionName(), buffer);
      }
      incrHeap = buffer.appendEntry(entry);
    }

    // If we crossed the chunk threshold, wait for more space to be available
    synchronized (controller.dataAvailable) {
      totalBuffered += incrHeap;
      while (totalBuffered > maxHeapUsage && controller.thrown.get() == null) {
        LOG.debug("Used {} bytes of buffered edits, waiting for IO threads", totalBuffered);
        controller.dataAvailable.wait(2000);
      }
      controller.dataAvailable.notifyAll();
    }
    controller.checkForErrors();
  }

  /**
   * @return RegionEntryBuffer a buffer of edits to be written.
   */
  synchronized RegionEntryBuffer getChunkToWrite() {
    long biggestSize = 0;
    byte[] biggestBufferKey = null;

    for (Map.Entry<byte[], RegionEntryBuffer> entry : buffers.entrySet()) {
      long size = entry.getValue().heapSize();
      if (size > biggestSize && (!currentlyWriting.contains(entry.getKey()))) {
        biggestSize = size;
        biggestBufferKey = entry.getKey();
      }
    }
    if (biggestBufferKey == null) {
      return null;
    }

    RegionEntryBuffer buffer = buffers.remove(biggestBufferKey);
    currentlyWriting.add(biggestBufferKey);
    return buffer;
  }

  void doneWriting(RegionEntryBuffer buffer) {
    synchronized (this) {
      boolean removed = currentlyWriting.remove(buffer.encodedRegionName);
      assert removed;
    }
    long size = buffer.heapSize();

    synchronized (controller.dataAvailable) {
      totalBuffered -= size;
      // We may unblock writers
      controller.dataAvailable.notifyAll();
    }
  }

  synchronized boolean isRegionCurrentlyWriting(byte[] region) {
    return currentlyWriting.contains(region);
  }

  /**
   * A buffer of some number of edits for a given region.
   * This accumulates edits and also provides a memory optimization in order to
   * share a single byte array instance for the table and region name.
   * Also tracks memory usage of the accumulated edits.
   */
  static class RegionEntryBuffer implements HeapSize {
    private long heapInBuffer = 0;
    final List<WAL.Entry> entryBuffer;
    final TableName tableName;
    final byte[] encodedRegionName;

    RegionEntryBuffer(TableName tableName, byte[] region) {
      this.tableName = tableName;
      this.encodedRegionName = region;
      this.entryBuffer = new ArrayList<>();
    }

    long appendEntry(WAL.Entry entry) {
      internify(entry);
      entryBuffer.add(entry);
      // TODO linkedlist entry
      long incrHeap = entry.getEdit().heapSize() +
          ClassSize.align(2 * ClassSize.REFERENCE); // WALKey pointers
      heapInBuffer += incrHeap;
      return incrHeap;
    }

    private void internify(WAL.Entry entry) {
      WALKeyImpl k = entry.getKey();
      k.internTableName(this.tableName);
      k.internEncodedRegionName(this.encodedRegionName);
    }

    @Override
    public long heapSize() {
      return heapInBuffer;
    }

    public byte[] getEncodedRegionName() {
      return encodedRegionName;
    }

    public TableName getTableName() {
      return tableName;
    }
  }
}