/**
   * Delete the specified snapshot
   *
   * @param snapshot
   * @throws SnapshotDoesNotExistException If the specified snapshot does not exist.
   * @throws IOException For filesystem IOExceptions
   */
  public void deleteSnapshot(SnapshotDescription snapshot)
      throws SnapshotDoesNotExistException, IOException {
    // check to see if it is completed
    if (!isSnapshotCompleted(snapshot)) {
      throw new SnapshotDoesNotExistException(ProtobufUtil.createSnapshotDesc(snapshot));
    }

    String snapshotName = snapshot.getName();
    // first create the snapshot description and check to see if it exists
    FileSystem fs = master.getMasterFileSystem().getFileSystem();
    Path snapshotDir = SnapshotDescriptionUtils.getCompletedSnapshotDir(snapshotName, rootDir);
    // Get snapshot info from file system. The one passed as parameter is a "fake" snapshotInfo with
    // just the "name" and it does not contains the "real" snapshot information
    snapshot = SnapshotDescriptionUtils.readSnapshotInfo(fs, snapshotDir);

    // call coproc pre hook
    MasterCoprocessorHost cpHost = master.getMasterCoprocessorHost();
    if (cpHost != null) {
      cpHost.preDeleteSnapshot(snapshot);
    }

    LOG.debug("Deleting snapshot: " + snapshotName);
    // delete the existing snapshot
    if (!fs.delete(snapshotDir, true)) {
      throw new HBaseSnapshotException("Failed to delete snapshot directory: " + snapshotDir);
    }

    // call coproc post hook
    if (cpHost != null) {
      cpHost.postDeleteSnapshot(snapshot);
    }
  }
  /**
   * Restore or Clone the specified snapshot
   *
   * @param reqSnapshot
   * @param nonceGroup unique value to prevent duplicated RPC
   * @param nonce unique value to prevent duplicated RPC
   * @throws IOException
   */
  public long restoreOrCloneSnapshot(
      SnapshotDescription reqSnapshot, final long nonceGroup, final long nonce) throws IOException {
    FileSystem fs = master.getMasterFileSystem().getFileSystem();
    Path snapshotDir = SnapshotDescriptionUtils.getCompletedSnapshotDir(reqSnapshot, rootDir);

    // check if the snapshot exists
    if (!fs.exists(snapshotDir)) {
      LOG.error("A Snapshot named '" + reqSnapshot.getName() + "' does not exist.");
      throw new SnapshotDoesNotExistException(ProtobufUtil.createSnapshotDesc(reqSnapshot));
    }

    // Get snapshot info from file system. The reqSnapshot is a "fake" snapshotInfo with
    // just the snapshot "name" and table name to restore. It does not contains the "real" snapshot
    // information.
    SnapshotDescription snapshot = SnapshotDescriptionUtils.readSnapshotInfo(fs, snapshotDir);
    SnapshotManifest manifest =
        SnapshotManifest.open(master.getConfiguration(), fs, snapshotDir, snapshot);
    HTableDescriptor snapshotTableDesc = manifest.getTableDescriptor();
    TableName tableName = TableName.valueOf(reqSnapshot.getTable());

    // stop tracking "abandoned" handlers
    cleanupSentinels();

    // Verify snapshot validity
    SnapshotReferenceUtil.verifySnapshot(master.getConfiguration(), fs, manifest);

    // Execute the restore/clone operation
    long procId;
    if (MetaTableAccessor.tableExists(master.getConnection(), tableName)) {
      procId =
          restoreSnapshot(reqSnapshot, tableName, snapshot, snapshotTableDesc, nonceGroup, nonce);
    } else {
      procId =
          cloneSnapshot(reqSnapshot, tableName, snapshot, snapshotTableDesc, nonceGroup, nonce);
    }
    return procId;
  }