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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.
 */

package org.apache.tephra.hbase.txprune;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Maps;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.client.Table;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.tephra.hbase.coprocessor.TransactionProcessor;
import org.apache.tephra.txprune.RegionPruneInfo;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;
import javax.annotation.Nullable;

/**
 * Persist data janitor state into an HBase table.
 * This is used by both {@link TransactionProcessor} and by the {@link HBaseTransactionPruningPlugin}
 * to persist and read the compaction state.
 */
@SuppressWarnings("WeakerAccess")
public class DataJanitorState {
  private static final Log LOG = LogFactory.getLog(DataJanitorState.class);

  public static final byte[] FAMILY = {'f'};
  public static final byte[] PRUNE_UPPER_BOUND_COL = {'p'};

  private static final byte[] REGION_TIME_COL = {'r'};
  private static final byte[] INACTIVE_TRANSACTION_BOUND_TIME_COL = {'i'};
  private static final byte[] EMPTY_REGION_TIME_COL = {'e'};

  private static final byte[] REGION_KEY_PREFIX = {0x1};
  private static final byte[] REGION_KEY_PREFIX_STOP = {0x2};

  private static final byte[] REGION_TIME_KEY_PREFIX = {0x2};
  private static final byte[] REGION_TIME_KEY_PREFIX_STOP = {0x3};

  private static final byte[] INACTIVE_TRANSACTION_BOUND_TIME_KEY_PREFIX = {0x3};
  private static final byte[] INACTIVE_TRANSACTION_BOUND_TIME_KEY_PREFIX_STOP = {0x4};

  private static final byte[] EMPTY_REGION_TIME_KEY_PREFIX = {0x4};
  private static final byte[] EMPTY_REGION_TIME_KEY_PREFIX_STOP = {0x5};

  private static final byte[] REGION_TIME_COUNT_KEY_PREFIX = {0x5};
  private static final byte[] REGION_TIME_COUNT_KEY_PREFIX_STOP = {0x6};

  private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];
  // This value can be used when we don't care about the value we write in a column
  private static final byte[] COL_VAL = Bytes.toBytes('1');

  private final TableSupplier stateTableSupplier;


  public DataJanitorState(TableSupplier stateTableSupplier) {
    this.stateTableSupplier = stateTableSupplier;
  }

  // ----------------------------------------------------------------
  // ------- Methods for prune upper bound for a given region -------
  // ----------------------------------------------------------------
  // The data is stored in the following format -
  // Key: 0x1
  // Col 'u': 
  // ----------------------------------------------------------------

  /**
   * Persist the latest prune upper bound for a given region. This is called by {@link TransactionProcessor}
   * after major compaction.
   *
   * @param regionId region id
   * @param pruneUpperBound the latest prune upper bound for the region
   * @throws IOException when not able to persist the data to HBase
   */
  public void savePruneUpperBoundForRegion(byte[] regionId, long pruneUpperBound) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      Put put = new Put(makeRegionKey(regionId));
      put.addColumn(FAMILY, PRUNE_UPPER_BOUND_COL, Bytes.toBytes(pruneUpperBound));
      stateTable.put(put);
    }
  }

  /**
   * Get latest prune upper bound for a given region. This indicates the largest invalid transaction that no
   * longer has writes in this region.
   *
   * @param regionId region id
   * @return latest prune upper bound for the region
   * @throws IOException when not able to read the data from HBase
   */
  public long getPruneUpperBoundForRegion(byte[] regionId) throws IOException {
    RegionPruneInfo regionPruneInfo = getPruneInfoForRegion(regionId);
    return (regionPruneInfo == null) ? -1 : regionPruneInfo.getPruneUpperBound();
  }

  /**
   * Get the latest {@link RegionPruneInfo} for a given region.
   *
   * @param regionId region id
   * @return {@link RegionPruneInfo} for the region
   * @throws IOException when not able to read the data from HBase
   */
  @Nullable
  public RegionPruneInfo getPruneInfoForRegion(byte[] regionId) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      Get get = new Get(makeRegionKey(regionId));
      get.addColumn(FAMILY, PRUNE_UPPER_BOUND_COL);
      Cell cell = stateTable.get(get).getColumnLatestCell(FAMILY, PRUNE_UPPER_BOUND_COL);
      if (cell == null) {
        return null;
      }
      byte[] pruneUpperBoundBytes = CellUtil.cloneValue(cell);
      long timestamp = cell.getTimestamp();
      return new RegionPruneInfo(regionId, Bytes.toStringBinary(regionId),
                                 Bytes.toLong(pruneUpperBoundBytes), timestamp);
    }
  }

  /**
   * Get latest prune upper bounds for given regions. This is a batch operation of method
   * {@link #getPruneUpperBoundForRegion(byte[])}
   *
   * @param regions a set of regions
   * @return a map containing region id and its latest prune upper bound value
   * @throws IOException when not able to read the data from HBase
   */
  public Map getPruneUpperBoundForRegions(SortedSet regions) throws IOException {
    Map resultMap = new TreeMap<>(Bytes.BYTES_COMPARATOR);
    List regionPruneInfos = getPruneInfoForRegions(regions);
    for (RegionPruneInfo regionPruneInfo : regionPruneInfos) {
      resultMap.put(regionPruneInfo.getRegionName(), regionPruneInfo.getPruneUpperBound());
    }
    return Collections.unmodifiableMap(resultMap);
  }

  /**
   * Gets a list of {@link RegionPruneInfo} for given regions. Returns all regions if the given regions set is null.
   *
   * @param regions a set of regions
   * @return list of {@link RegionPruneInfo}s.
   * @throws IOException when not able to read the data from HBase
   */
  public List getPruneInfoForRegions(@Nullable SortedSet regions) throws IOException {
    List regionPruneInfos = new ArrayList<>();
    try (Table stateTable = stateTableSupplier.get()) {
      byte[] startRow = makeRegionKey(EMPTY_BYTE_ARRAY);
      Scan scan = new Scan(startRow, REGION_KEY_PREFIX_STOP);
      scan.addColumn(FAMILY, PRUNE_UPPER_BOUND_COL);

      try (ResultScanner scanner = stateTable.getScanner(scan)) {
        Result next;
        while ((next = scanner.next()) != null) {
          byte[] region = getRegionFromKey(next.getRow());
          if (regions == null || regions.contains(region)) {
            Cell cell = next.getColumnLatestCell(FAMILY, PRUNE_UPPER_BOUND_COL);
            if (cell != null) {
              byte[] pruneUpperBoundBytes = CellUtil.cloneValue(cell);
              long timestamp = cell.getTimestamp();
              regionPruneInfos.add(new RegionPruneInfo(region, Bytes.toStringBinary(region),
                                                       Bytes.toLong(pruneUpperBoundBytes), timestamp));
            }
          }
        }
      }
    }
    return Collections.unmodifiableList(regionPruneInfos);
  }

  /**
   * Delete prune upper bounds for the regions that are not in the given exclude set, and the
   * prune upper bound is less than the given value.
   * After the invalid list is pruned up to deletionPruneUpperBound, we do not need entries for regions that have
   * prune upper bound less than deletionPruneUpperBound. We however limit the deletion to only regions that are
   * no longer in existence (due to deletion, etc.), to avoid update/delete race conditions.
   *
   * @param deletionPruneUpperBound prune upper bound below which regions will be deleted
   * @param excludeRegions set of regions that should not be deleted
   * @throws IOException when not able to delete data in HBase
   */
  public void deletePruneUpperBounds(long deletionPruneUpperBound, SortedSet excludeRegions)
    throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      byte[] startRow = makeRegionKey(EMPTY_BYTE_ARRAY);
      Scan scan = new Scan(startRow, REGION_KEY_PREFIX_STOP);
      scan.addColumn(FAMILY, PRUNE_UPPER_BOUND_COL);

      try (ResultScanner scanner = stateTable.getScanner(scan)) {
        Result next;
        while ((next = scanner.next()) != null) {
          byte[] region = getRegionFromKey(next.getRow());
          if (!excludeRegions.contains(region)) {
            byte[] timeBytes = next.getValue(FAMILY, PRUNE_UPPER_BOUND_COL);
            if (timeBytes != null) {
              long pruneUpperBoundRegion = Bytes.toLong(timeBytes);
              if (pruneUpperBoundRegion < deletionPruneUpperBound) {
                stateTable.delete(new Delete(next.getRow()));
              }
            }
          }
        }
      }
    }
  }

  // ---------------------------------------------------
  // ------- Methods for regions at a given time -------
  // ---------------------------------------------------
  // Key: 0x2
  // Col 't': 
  // ---------------------------------------------------

  /**
   * Persist the regions for the given time. {@link HBaseTransactionPruningPlugin} saves the set of
   * transactional regions existing in the HBase instance periodically.
   *
   * @param time timestamp in milliseconds
   * @param regions set of regions at the time
   * @throws IOException when not able to persist the data to HBase
   */
  public void saveRegionsForTime(long time, Set regions) throws IOException {
    byte[] timeBytes = Bytes.toBytes(getInvertedTime(time));
    try (Table stateTable = stateTableSupplier.get()) {
      for (byte[] region : regions) {
        Put put = new Put(makeTimeRegionKey(timeBytes, region));
        put.addColumn(FAMILY, REGION_TIME_COL, COL_VAL);
        stateTable.put(put);
      }

      // Save the count of regions as a checksum
      saveRegionCountForTime(stateTable, timeBytes, regions.size());
    }
  }

  @VisibleForTesting
  void saveRegionCountForTime(Table stateTable, byte[] timeBytes, int count) throws IOException {
    Put put = new Put(makeTimeRegionCountKey(timeBytes));
    put.addColumn(FAMILY, REGION_TIME_COL, Bytes.toBytes(count));
    stateTable.put(put);
  }

  /**
   * Return the set of regions saved for the time at or before the given time. This method finds the greatest time
   * that is less than or equal to the given time, and then returns all regions with that exact time, but none that are
   * older than that.
   *
   * @param time timestamp in milliseconds
   * @return set of regions and time at which they were recorded, or null if no regions found
   * @throws IOException when not able to read the data from HBase
   */
  @Nullable
  public TimeRegions getRegionsOnOrBeforeTime(long time) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      TimeRegions timeRegions;
      while ((timeRegions = getNextSetOfTimeRegions(stateTable, time)) != null) {
        int count = getRegionCountForTime(stateTable, timeRegions.getTime());
        if (count != -1 && count == timeRegions.getRegions().size()) {
          return timeRegions;
        } else {
          LOG.warn(String.format("Got incorrect count for regions saved at time %s, expected = %s but actual = %s",
                                 timeRegions.getTime(), count, timeRegions.getRegions().size()));
          time = timeRegions.getTime() - 1;
        }
      }
      return null;
    }
  }

  @Nullable
  private TimeRegions getNextSetOfTimeRegions(Table stateTable, long time) throws IOException {
    byte[] timeBytes = Bytes.toBytes(getInvertedTime(time));
    Scan scan = new Scan(makeTimeRegionKey(timeBytes, EMPTY_BYTE_ARRAY), REGION_TIME_KEY_PREFIX_STOP);
    scan.addColumn(FAMILY, REGION_TIME_COL);


    long currentRegionTime = -1;
    SortedSet regions = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    Result next;
    try (ResultScanner scanner = stateTable.getScanner(scan)) {
      while ((next = scanner.next()) != null) {
        Map.Entry timeRegion = getTimeRegion(next.getRow());
        // Stop if reached next time value
        if (currentRegionTime == -1) {
          currentRegionTime = timeRegion.getKey();
        } else if (timeRegion.getKey() < currentRegionTime) {
          break;
        } else if (timeRegion.getKey() > currentRegionTime) {
          throw new IllegalStateException(
            String.format("Got out of order time %d when expecting time less than or equal to %d",
                          timeRegion.getKey(), currentRegionTime));
        }
        regions.add(timeRegion.getValue());
      }
    }
    return regions.isEmpty() ? null : new TimeRegions(currentRegionTime, Collections.unmodifiableSortedSet(regions));
  }

  @VisibleForTesting
  int getRegionCountForTime(Table stateTable, long time) throws IOException {
    Get get = new Get(makeTimeRegionCountKey(Bytes.toBytes(getInvertedTime(time))));
    get.addColumn(FAMILY, REGION_TIME_COL);
    Result result = stateTable.get(get);
    byte[] value = result.getValue(FAMILY, REGION_TIME_COL);
    return value == null ? -1 : Bytes.toInt(value);
  }

  /**
   * Delete all the regions that were recorded for all times equal or less than the given time.
   *
   * @param time timestamp in milliseconds
   * @throws IOException when not able to delete data in HBase
   */
  public void deleteAllRegionsOnOrBeforeTime(long time) throws IOException {
    byte[] timeBytes = Bytes.toBytes(getInvertedTime(time));
    try (Table stateTable = stateTableSupplier.get()) {
      // Delete the regions
      Scan scan = new Scan(makeTimeRegionKey(timeBytes, EMPTY_BYTE_ARRAY), REGION_TIME_KEY_PREFIX_STOP);
      scan.addColumn(FAMILY, REGION_TIME_COL);
      deleteFromScan(stateTable, scan);

      // Delete the count
      scan = new Scan(makeTimeRegionCountKey(timeBytes), REGION_TIME_COUNT_KEY_PREFIX_STOP);
      scan.addColumn(FAMILY, REGION_TIME_COL);
      deleteFromScan(stateTable, scan);
    }
  }

  // ---------------------------------------------------------------------
  // ------- Methods for inactive transaction bound for given time -------
  // ---------------------------------------------------------------------
  // Key: 0x3
  // Col 'p': 
  // ---------------------------------------------------------------------

  /**
   * Persist inactive transaction bound for a given time. This is the smallest not in-progress transaction that
   * will not have writes in any HBase regions that are created after the given time.
   *
   * @param time time in milliseconds
   * @param inactiveTransactionBound inactive transaction bound for the given time
   * @throws IOException when not able to persist the data to HBase
   */
  public void saveInactiveTransactionBoundForTime(long time, long inactiveTransactionBound) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      Put put = new Put(makeInactiveTransactionBoundTimeKey(Bytes.toBytes(getInvertedTime(time))));
      put.addColumn(FAMILY, INACTIVE_TRANSACTION_BOUND_TIME_COL, Bytes.toBytes(inactiveTransactionBound));
      stateTable.put(put);
    }
  }

  /**
   * Return inactive transaction bound for the given time.
   *
   * @param time time in milliseconds
   * @return inactive transaction bound for the given time
   * @throws IOException when not able to read the data from HBase
   */
  public long getInactiveTransactionBoundForTime(long time) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      Get get = new Get(makeInactiveTransactionBoundTimeKey(Bytes.toBytes(getInvertedTime(time))));
      get.addColumn(FAMILY, INACTIVE_TRANSACTION_BOUND_TIME_COL);
      byte[] result = stateTable.get(get).getValue(FAMILY, INACTIVE_TRANSACTION_BOUND_TIME_COL);
      return result == null ? -1 : Bytes.toLong(result);
    }
  }

  /**
   * Delete all inactive transaction bounds recorded for a time less than the given time
   *
   * @param time time in milliseconds
   * @throws IOException when not able to delete data in HBase
   */
  public void deleteInactiveTransactionBoundsOnOrBeforeTime(long time) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      Scan scan = new Scan(makeInactiveTransactionBoundTimeKey(Bytes.toBytes(getInvertedTime(time))),
                           INACTIVE_TRANSACTION_BOUND_TIME_KEY_PREFIX_STOP);
      scan.addColumn(FAMILY, INACTIVE_TRANSACTION_BOUND_TIME_COL);
      deleteFromScan(stateTable, scan);
    }
  }

  // --------------------------------------------------------
  // ------- Methods for empty regions at a given time -------
  // --------------------------------------------------------
  // Key: 0x4
  // Col 'e': 
  // --------------------------------------------------------

  /**
   * Save the given region as empty as of the given time.
   *
   * @param time time in milliseconds
   * @param regionId region id
   */
  public void saveEmptyRegionForTime(long time, byte[] regionId) throws IOException {
    byte[] timeBytes = Bytes.toBytes(time);
    try (Table stateTable = stateTableSupplier.get()) {
      Put put = new Put(makeEmptyRegionTimeKey(timeBytes, regionId));
      put.addColumn(FAMILY, EMPTY_REGION_TIME_COL, COL_VAL);
      stateTable.put(put);
    }
  }

  /**
   * Return regions that were recorded as empty after the given time.
   *
   * @param time time in milliseconds
   * @param includeRegions If not null, the returned set will be an intersection of the includeRegions set
   *                       and the empty regions after the given time
   */
  public SortedSet getEmptyRegionsAfterTime(long time, @Nullable SortedSet includeRegions)
    throws IOException {
    SortedSet emptyRegions = new TreeSet<>(Bytes.BYTES_COMPARATOR);
    try (Table stateTable = stateTableSupplier.get()) {
      Scan scan = new Scan(makeEmptyRegionTimeKey(Bytes.toBytes(time + 1), EMPTY_BYTE_ARRAY),
                           EMPTY_REGION_TIME_KEY_PREFIX_STOP);
      scan.addColumn(FAMILY, EMPTY_REGION_TIME_COL);

      try (ResultScanner scanner = stateTable.getScanner(scan)) {
        Result next;
        while ((next = scanner.next()) != null) {
          byte[] emptyRegion = getEmptyRegionFromKey(next.getRow());
          if (includeRegions == null || includeRegions.contains(emptyRegion)) {
            emptyRegions.add(emptyRegion);
          }
        }
      }
    }
    return Collections.unmodifiableSortedSet(emptyRegions);
  }

  /**
   * Delete empty region records saved on or before the given time.
   *
   * @param time time in milliseconds
   */
  public void deleteEmptyRegionsOnOrBeforeTime(long time) throws IOException {
    try (Table stateTable = stateTableSupplier.get()) {
      Scan scan = new Scan();
      scan.setStopRow(makeEmptyRegionTimeKey(Bytes.toBytes(time + 1), EMPTY_BYTE_ARRAY));
      scan.addColumn(FAMILY, EMPTY_REGION_TIME_COL);
      deleteFromScan(stateTable, scan);
    }
  }

  @VisibleForTesting
  void deleteFromScan(Table stateTable, Scan scan) throws IOException {
    try (ResultScanner scanner = stateTable.getScanner(scan)) {
      Result next;
      while ((next = scanner.next()) != null) {
        stateTable.delete(new Delete(next.getRow()));
      }
    }
  }

  private byte[] makeRegionKey(byte[] regionId) {
    return Bytes.add(REGION_KEY_PREFIX, regionId);
  }

  private byte[] getRegionFromKey(byte[] regionKey) {
    int prefixLen = REGION_KEY_PREFIX.length;
    return Bytes.copy(regionKey, prefixLen, regionKey.length - prefixLen);
  }

  private byte[] makeTimeRegionKey(byte[] time, byte[] regionId) {
    return Bytes.add(REGION_TIME_KEY_PREFIX, time, regionId);
  }

  private byte[] makeTimeRegionCountKey(byte[] time) {
    return Bytes.add(REGION_TIME_COUNT_KEY_PREFIX, time);
  }

  private byte[] makeInactiveTransactionBoundTimeKey(byte[] time) {
    return Bytes.add(INACTIVE_TRANSACTION_BOUND_TIME_KEY_PREFIX, time);
  }

  private Map.Entry getTimeRegion(byte[] key) {
    int offset = REGION_TIME_KEY_PREFIX.length;
    long time = getInvertedTime(Bytes.toLong(key, offset));
    offset += Bytes.SIZEOF_LONG;
    byte[] regionName = Bytes.copy(key, offset, key.length - offset);
    return Maps.immutableEntry(time, regionName);
  }

  private byte[] makeEmptyRegionTimeKey(byte[] time, byte[] regionId) {
    return Bytes.add(EMPTY_REGION_TIME_KEY_PREFIX, time, regionId);
  }

  private byte[] getEmptyRegionFromKey(byte[] key) {
    int prefixLen = EMPTY_REGION_TIME_KEY_PREFIX.length + Bytes.SIZEOF_LONG;
    return Bytes.copy(key, prefixLen, key.length - prefixLen);
  }

  private long getInvertedTime(long time) {
    return Long.MAX_VALUE - time;
  }

  /**
   * Supplies table for persisting state
   */
  public interface TableSupplier {
    Table get() throws IOException;
  }
}