apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/grayReleaseRule/GrayReleaseRulesHolder.java/GrayReleaseRulesHolder/afterPropertiesSet
class GrayReleaseRulesHolder:  @Override
  public void afterPropertiesSet() throws Exception {
    populateDataBaseInterval();
    //force sync load for the first time
    periodicScanRules();
    executorService.scheduleWithFixedDelay(this::periodicScanRules,
        getDatabaseScanIntervalSecond(), getDatabaseScanIntervalSecond(), getDatabaseScanTimeUnit()
    );
  }