@Override
            public synchronized void onSingleValueChanged(final WatcherHolder holder, final ConfigTable.ConfigItem configItem) {
                notifySingleValue(holder.getWatcher(), configItem);
            }
Implement Config Watcher register using client listening.
oap-server/server-configuration/configuration-api/src/main/java/org/apache/skywalking/oap/server/configuration/api/ListeningConfigWatcherRegister.java