huwenming-saw commented on issue #10393:
URL: https://github.com/apache/dubbo/issues/10393#issuecomment-1263358980
> > @404008945 provider 和 consumer 都升级，2.7 的早期有个版本注册是有问题的
>
> @AlbumenJ 问题找到了。
生产和消费者都是升级了最新版的2.7.16，另外nacos-client为1.3.3时有问题，**测试nacos-client版本为2.0.4已经没有问题了**
**问题记录** 生产者注册服务名称逻辑为 org.apache.dubbo.common.URL#getColonSeparatedKey
>
> ```java
> public String getColonSeparatedKey() {
> StringBuilder serviceNameBuilder = new StringBuilder();
> serviceNameBuilder.append(this.getServiceInterface());
> append(serviceNameBuilder, VERSION_KEY, false);
> append(serviceNameBuilder, GROUP_KEY, false);
> return serviceNameBuilder.toString();
> }
> ```
>
> 当version为空时并不会省略掉间隔符冒号 于是注册的服务名称是
io.seata.samples.tcc.dubbo.action.TccActionOne::tcc
>
> 然后我又看了消费者启动时初始化invoke时，生成的订阅服务名称逻辑
org.apache.dubbo.registry.nacos.NacosRegistry#getServiceNames0
>
> ```java
> private Set<String> getServiceNames0(URL url) {
> NacosServiceName serviceName = createServiceName(url);
>
> final Set<String> serviceNames;
>
> if (serviceName.isConcrete()) { // is the concrete service name
> serviceNames = new LinkedHashSet<>();
> serviceNames.add(serviceName.toString());
> // Add the legacy service name since 2.7.6
> String legacySubscribedServiceName =
getLegacySubscribedServiceName(url);
> if
(!serviceName.toString().equals(legacySubscribedServiceName)) {
> //avoid duplicated service names
> serviceNames.add(legacySubscribedServiceName);
> }
> } else {
> serviceNames = filterServiceNames(serviceName);
> }
>
> return serviceNames;
> }
> ```
>
>
version为空，新版服务名version为空，不会省略间隔符冒号,根据注释，为了兼容2.7.3以前的版本，另外生成服务名
version为空并且把冒号也省略掉了。最终结果就是新版比旧版多了一个冒号。 后面会继续分别订阅这两个服务名称,其中一个服务名在注册中心不存在，是空服务。
org.apache.dubbo.registry.nacos.NacosRegistry#doSubscribe(org.apache.dubbo.common.URL,
org.apache.dubbo.registry.NotifyListener, java.util.Set<java.lang.String>)
>
> ```java
> private void doSubscribe(final URL url, final NotifyListener listener,
final Set<String> serviceNames) {
> execute(namingService -> {
> if (isServiceNamesWithCompatibleMode(url)) {
> List<Instance> allCorrespondingInstanceList =
Lists.newArrayList();
>
> /**
> * Get all instances with serviceNames to avoid instance
overwrite and but with empty instance mentioned
> * in https://github.com/apache/dubbo/issues/5885 and
https://github.com/apache/dubbo/issues/5899
> *
> * namingService.getAllInstances with {@link
org.apache.dubbo.registry.support.AbstractRegistry#registryUrl}
> * default {@link DEFAULT_GROUP}
> *
> * in https://github.com/apache/dubbo/issues/5978
> */
> for (String serviceName : serviceNames) {
> List<Instance> instances =
namingService.getAllInstances(serviceName,
> getUrl().getParameter(GROUP_KEY,
Constants.DEFAULT_GROUP));
>
NacosInstanceManageUtil.initOrRefreshServiceInstanceList(serviceName,
instances);
> allCorrespondingInstanceList.addAll(instances);
> }
> notifySubscriber(url, listener,
allCorrespondingInstanceList);
> for (String serviceName : serviceNames) {
> subscribeEventListener(serviceName, url, listener);
> }
> } else {
> List<Instance> instances = new LinkedList<>();
> for (String serviceName : serviceNames) {
>
instances.addAll(namingService.getAllInstances(serviceName
> , getUrl().getParameter(GROUP_KEY,
Constants.DEFAULT_GROUP)));
> notifySubscriber(url, listener, instances);
> subscribeEventListener(serviceName, url, listener);
> }
> }
>
> });
> }
> ```
>
> 上面有段很好的注释 ，**Get all instances with serviceNames to avoid instance
overwrite and but with empty instance mentioned**获取所有的serviceNames
的实例，防止被空的实例覆盖。看起来好像没有问题。 但是下面的循环serviceNames订阅
>
> ```java
> for (String serviceName : serviceNames) {
> subscribeEventListener(serviceName, url, listener);
> }
> ```
>
> 但是注册中心为nacos时 这里来到了nacos客户端 版本为1.3.3时
>
> ```java
> public void addListener(ServiceInfo serviceInfo, String clusters,
EventListener listener) {
>
> NAMING_LOGGER.info("[LISTENER] adding " + serviceInfo.getName() +
" with " + clusters + " to listener map");
> List<EventListener> observers = Collections.synchronizedList(new
ArrayList<EventListener>());
> observers.add(listener);
>
> observers =
observerMap.putIfAbsent(ServiceInfo.getKey(serviceInfo.getName(), clusters),
observers);
> if (observers != null) {
> observers.add(listener);
> }
>
> serviceChanged(serviceInfo);
> }
>
> ```
>
>
会发现在第一次添加监听器时还是会触发serviceChange，进而触发notify，重新刷新invoker，由于实例为空的服务名也被订阅，那么这时候还是可能会发生被空的实例覆盖的情况。
问一下您，看您的描述，即使升级到“生产和消费者都是升级了最新版的2.7.16，另外nacos-client为1.3.3时有问题，测试nacos-client版本为2.0.4已经没有问题了”您说的这种情况中的dubbo-2.7.16，nacos-2.0.4，还是会订阅一个空服务，这个空服务对应的接口还是同一个URL，这个时候难道就不会出现No
provider available？；换另一个角度来说最好的解决方法还是需要提供group version值是最完美的解决方法是吗？期待您的回复，这个No
provider available困扰我很久了
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