apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/grayReleaseRule/GrayReleaseRulesHolder.java/GrayReleaseRulesHolder/periodicScanRules
class GrayReleaseRulesHolder:  private void periodicScanRules() {
    Transaction transaction = Tracer.newTransaction("Apollo.GrayReleaseRulesScanner",
        "scanGrayReleaseRules");
    try {
      loadVersion.incrementAndGet();
      scanGrayReleaseRules();
      transaction.setStatus(Transaction.SUCCESS);
    } catch (Throwable ex) {
      transaction.setStatus(ex);
      logger.error("Scan gray release rule failed", ex);
    } finally {
      transaction.complete();
    }
  }