apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/service/ReleaseMessageServiceWithCache.java/ReleaseMessageServiceWithCache/mergeReleaseMessage
class ReleaseMessageServiceWithCache:  private synchronized void mergeReleaseMessage(ReleaseMessage releaseMessage) {
    ReleaseMessage old = releaseMessageCache.get(releaseMessage.getMessage());
    if (old == null || releaseMessage.getId() > old.getId()) {
      releaseMessageCache.put(releaseMessage.getMessage(), releaseMessage);
      maxIdScanned = releaseMessage.getId();
    }
  }