public static LoggingLevel getLoggingLevel (String mode) {
    String m = StringUtils.defaultString(mode).toLowerCase();
    switch (m) {
    case "none":
      return LoggingLevel.NONE;
    case "execution":
      return LoggingLevel.EXECUTION;
    case "verbose":
      return LoggingLevel.VERBOSE;
    case "performance":
      return LoggingLevel.PERFORMANCE;
    default:
      return LoggingLevel.UNKNOWN;
    }
  }
OperationLog wraps the actual operation log file, and provides interface
for accessing, reading, writing, and removing the file.
ql/src/java/org/apache/hadoop/hive/ql/session/OperationLog.java