private static Optional<TimedQuota> buildDefaultTimedQuota(Configuration conf, String key) {
    int defaultSoftLimit = conf.getInt(key, -1);
    if (defaultSoftLimit == -1) {
      return Optional.empty();
    }
    return Optional.of(ProtobufUtil.toTimedQuota(defaultSoftLimit,
      java.util.concurrent.TimeUnit.SECONDS, org.apache.hadoop.hbase.quotas.QuotaScope.MACHINE));
  }
Returns true if the support for quota is enabled
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/QuotaUtil.java