private boolean isValid(final Connection connection) {
    if (connection == null) {
      return false;
    }

    if (status != PwmService.STATUS.OPEN) {
      return false;
    }

    try {
      final Method getFreeSpaceMethod = File.class.getMethod("isValid");
      final Object rawResult = getFreeSpaceMethod.invoke(connection, 10);
      return (Boolean) rawResult;
    } catch (NoSuchMethodException e) {
      /* no error, pre java 1.6 doesn't have this method */
    } catch (Exception e) {
      LOGGER.debug(
          "error checking for isValid for " + connection.toString() + ",: " + e.getMessage());
    }

    final StringBuilder sb = new StringBuilder();
    sb.append("SELECT * FROM ")
        .append(DatabaseTable.PWM_META.toString())
        .append(" WHERE " + KEY_COLUMN + " = ?");
    PreparedStatement statement = null;
    ResultSet resultSet = null;
    try {
      statement = connection.prepareStatement(sb.toString());
      statement.setString(1, KEY_ENGINE_START_PREFIX + instanceID);
      statement.setMaxRows(1);
      resultSet = statement.executeQuery();
      if (resultSet.next()) {
        resultSet.getString(VALUE_COLUMN);
      }
    } catch (SQLException e) {
      final ErrorInformation errorInformation =
          new ErrorInformation(
              PwmError.ERROR_DB_UNAVAILABLE, "isValid operation failed: " + e.getMessage());
      lastError = errorInformation;
      LOGGER.error(errorInformation.toDebugStr());
      return false;
    } finally {
      close(statement);
      close(resultSet);
    }
    return true;
  }
  @Override
  public String get(final DatabaseTable table, final String key) throws DatabaseException {
    if (traceLogging) {
      LOGGER.trace("attempting get operation for table=" + table + ", key=" + key);
    }
    preOperationCheck();
    final StringBuilder sb = new StringBuilder();
    sb.append("SELECT * FROM ").append(table.toString()).append(" WHERE " + KEY_COLUMN + " = ?");

    PreparedStatement statement = null;
    ResultSet resultSet = null;
    String returnValue = null;
    try {
      statement = connection.prepareStatement(sb.toString());
      statement.setString(1, key);
      statement.setMaxRows(1);
      resultSet = statement.executeQuery();

      if (resultSet.next()) {
        returnValue = resultSet.getString(VALUE_COLUMN);
      }
    } catch (SQLException e) {
      final ErrorInformation errorInformation =
          new ErrorInformation(
              PwmError.ERROR_DB_UNAVAILABLE, "get operation failed: " + e.getMessage());
      lastError = errorInformation;
      throw new DatabaseException(errorInformation);
    } finally {
      close(statement);
      close(resultSet);
    }

    if (traceLogging) {
      final LinkedHashMap<String, Object> debugOutput = new LinkedHashMap<>();
      debugOutput.put("table", table);
      debugOutput.put("key", key);
      debugOutput.put("result", returnValue);
      LOGGER.trace(
          "get operation result: " + JsonUtil.serializeMap(debugOutput, JsonUtil.Flag.PrettyPrint));
    }

    updateStats(true, false);
    return returnValue;
  }
  @Override
  public boolean remove(final DatabaseTable table, final String key) throws DatabaseException {
    if (traceLogging) {
      LOGGER.trace("attempting remove operation for table=" + table + ", key=" + key);
    }

    boolean result = contains(table, key);
    if (result) {
      final StringBuilder sqlText = new StringBuilder();
      sqlText.append("DELETE FROM ").append(table.toString()).append(" WHERE " + KEY_COLUMN + "=?");

      PreparedStatement statement = null;
      try {
        statement = connection.prepareStatement(sqlText.toString());
        statement.setString(1, key);
        statement.executeUpdate();
        LOGGER.trace("remove operation succeeded for table=" + table + ", key=" + key);
      } catch (SQLException e) {
        final ErrorInformation errorInformation =
            new ErrorInformation(
                PwmError.ERROR_DB_UNAVAILABLE, "remove operation failed: " + e.getMessage());
        lastError = errorInformation;
        throw new DatabaseException(errorInformation);
      } finally {
        close(statement);
      }
    }

    if (traceLogging) {
      final Map<String, Object> debugOutput = new LinkedHashMap<>();
      debugOutput.put("table", table);
      debugOutput.put("key", key);
      debugOutput.put("result", result);
      LOGGER.trace(
          "remove operation result: "
              + JsonUtil.serializeMap(debugOutput, JsonUtil.Flag.PrettyPrint));
    }

    updateStats(true, false);
    return result;
  }
  @Override
  public boolean put(final DatabaseTable table, final String key, final String value)
      throws DatabaseException {

    preOperationCheck();
    if (traceLogging) {
      LOGGER.trace("attempting put operation for table=" + table + ", key=" + key);
    }
    if (!contains(table, key)) {
      final String sqlText =
          "INSERT INTO "
              + table.toString()
              + "("
              + KEY_COLUMN
              + ", "
              + VALUE_COLUMN
              + ") VALUES(?,?)";
      PreparedStatement statement = null;

      try {
        statement = connection.prepareStatement(sqlText);
        statement.setString(1, key);
        statement.setString(2, value);
        statement.executeUpdate();
      } catch (SQLException e) {
        final ErrorInformation errorInformation =
            new ErrorInformation(
                PwmError.ERROR_DB_UNAVAILABLE, "put operation failed: " + e.getMessage());
        lastError = errorInformation;
        throw new DatabaseException(errorInformation);
      } finally {
        close(statement);
      }
      return false;
    }

    final String sqlText =
        "UPDATE " + table.toString() + " SET " + VALUE_COLUMN + "=? WHERE " + KEY_COLUMN + "=?";
    PreparedStatement statement = null;

    try {
      statement = connection.prepareStatement(sqlText);
      statement.setString(1, value);
      statement.setString(2, key);
      statement.executeUpdate();
    } catch (SQLException e) {
      final ErrorInformation errorInformation =
          new ErrorInformation(
              PwmError.ERROR_DB_UNAVAILABLE, "put operation failed: " + e.getMessage());
      lastError = errorInformation;
      throw new DatabaseException(errorInformation);
    } finally {
      close(statement);
    }

    if (traceLogging) {
      final Map<String, Object> debugOutput = new LinkedHashMap<>();
      debugOutput.put("table", table);
      debugOutput.put("key", key);
      debugOutput.put("value", value);
      LOGGER.trace(
          "put operation result: " + JsonUtil.serializeMap(debugOutput, JsonUtil.Flag.PrettyPrint));
    }

    updateStats(false, true);
    return true;
  }