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How to recover client from "No handler waiting for message" warning?

At medium to high load (test and production), when using the Vert.x Redis client, I get the following warning after a few hundred requests.
2019-11-22 11:30:02.320 [vert.x-eventloop-thread-1] WARN io.vertx.redis.client.impl.RedisClient - No handler waiting for message: [null, 400992, <data from redis>]
As a result, the handler supplied to the Redis call (see below) does not get called and the incoming request times out.
Handler<AsyncResult<String>> handler = res -> {
// success handler
};
redis.get(key, res -> {
handler.handle(res);
});
The real issue is that once the "No handler ..." warning comes up, the Redis client becomes useless because all further calls to Redis made via the client fails with the same warning resulting in the handler not getting called. I have an exception handler set on the client to attempt reconnection, but I do not see any reconnections being attempted.
How can one recover from this problem? Any workarounds to alleviate the severity would also be great.
I'm on vertx-core and vertx-redis-client 3.8.1 .

The upcoming 4.0 release had addressed this issue and a release should be hapening soon, how soon, I can't really tell.
The problem is that we can't easily port back from the master branch to the 3.8 branch because a major refactoring has happened on the client and the codebases are very different.
The new code, uses a connection pool and has been tested for concurrent access (and this is where the issue you're seeing comes from). Under load the requests are routed across all event loops and the queue that maintains the state between in flight requests (requests sent to redis) and waiting handlers would get out of sync in very special conditions.
So I'd first try to see if you can already start moving your code to 4.0, you can have a try with the 4.0.0-milestone3 version but to be totally fine, just have a run with the latest master which has more issues solved in this area.

Understanding Long Polling Client Logic for Use With Azure Groovy Java

Premise:
We have groovy scripts that execute every minute. I want one of those scripts to open an HTTP client, and poll a service bus queue / topic for messages. I have my rest client code working an getting messages from the service bus queue. I can do a "Get" every 5 seconds, and wireshark shows that it's reusing the same TCP connection which is better than I expected, but its still not ideal.
Goal:
I would like to make this http client do "long polling", for efficiency and to achieve actual real-time processing. It seems to be more complicated than I anticipated.
Problem:
When I do a "Delete" call to read message from a service bus queue, it immediately returns "HTTP/1.1 204 No Content", and the connection closes. I set a timeout on the client, but I don't think that matters.
Here's the article that shows service bus says it's supports long polling, which I imagine is the hard part. Azure Service Bus Queues
I feel that I don't understand something fundamental about how to implement long polling in code. My understanding is that when there is no data in the queue, it's supposed to delay the response until data exists, or until my client eventually times out waiting (which lets me set my own disconnect/reconnect interval). I don't even care about blocking/nonblocking etc, because the script execution is already spreadout into a threadpool, and will be terminated forcibly and all that.
Any help is greatly appreciated.

The correct and simple answer is that adding the following to the end of an Azure REST API URL (with service bus) is the way to implements long-polling with that service: ?timeout=60 , where 60 tells azure to wait 60 seconds before responding with no-data. So, your application can check for data every 60 seconds, with an internal timeout of 60 seconds on each HTTP request. This will hold the TCP connection open for that timeframe, waiting for an HTTP response.

For understanding long polling, I recommend you can learn the entry Comet of Wiki https://en.wikipedia.org/wiki/Comet_(programming). And there is an answered thread (Long polling in java) explained the mechanism of the HttpURLConnection Class support long polling in Java.
As I know, a simple way in Java Client instead of HttpURLConnection is using the client library of CometD. You can refer to the section Client Library of its offical document https://docs.cometd.org/current/reference/#_java_client to learn how to implement the long polling client in Java. You can download the library at https://download.cometd.org/.
The sample code from the offical document:
// Create (and eventually set up) Jetty's HttpClient:
HttpClient httpClient = new HttpClient();
httpClient.start();
// Prepare the transport
Map<String, Object> options = new HashMap<String, Object>();
ClientTransport transport = new LongPollingTransport(options, httpClient);
// Create the BayeuxClient
ClientSession client = new BayeuxClient("http://localhost:8080/cometd", transport);
// Here set up the BayeuxClient, for example:
// client.getChannel(Channel.META_CONNECT).addListener(new ClientSessionChannel.MessageListener() {
public void onMessage(ClientSessionChannel channel, Message message) {
if (message.isSuccessful()) {
// Here handshake is successful
}
}
});
client.handshake();
Note: There are two REST API of Azure Service Bus for getting messaging entity(s) Get Entity https://msdn.microsoft.com/en-us/library/azure/hh780754.aspx and Entities Discovery https://msdn.microsoft.com/en-us/library/azure/hh780782.aspx. You need to delete the used messaging entity manually thru the Delete Entity REST API. Requesting all of these REST API first require an access_token thru the post request the Request a Token from ACS API for secure access.

Difference between web service connection timeout and request timeout

WebClientTestService service = new WebClientTestService() ;
int connectionTimeOutInMs = 5000;
Map<String,Object> context=((BindingProvider)service).getRequestContext();
context.put("com.sun.xml.internal.ws.connect.timeout", connectionTimeOutInMs);
context.put("com.sun.xml.internal.ws.request.timeout", connectionTimeOutInMs);
context.put("com.sun.xml.ws.request.timeout", connectionTimeOutInMs);
context.put("com.sun.xml.ws.connect.timeout", connectionTimeOutInMs);
Please share the differences mainly in connect timeout and request timeout.
I need to know the recommended values for these parameter values.
What are the criteria for setting timeout value ?

Please share the differences mainly in connect timeout and request timeout.
I need to know the recommended values for these parameter values.
Connect timeout (10s-30s): How long to wait to make an initial connection e.g. if service is currently unavailable.
Socket timeout (10s-20s): How long to wait if the service stops responding after data is sent.
Request timeout (30s-300s): How long to wait for the entire request to complete.
What are the criteria for setting timeout value ?
It depends a web user will get impatient if nothing has happened after 1-2 minutes, however a back end request could be allowed to run longer.
Also consider server resources are not released until request completes (or times out) - so if you have too many requests and long timeouts your server could run out of resources and be unable to service further requests.
request timeout should be set to a value greater then the expected time for the request to complete, perhaps with some room to allow occasionally slower performance under heavy loads.
connect/socket timeouts are often set lower as normally indicate a server problem where waiting another 10-15s usually won't resolve.

Reusing the SOAP client with Axis

I'm using Apache Axis to make a SOAP request to a service. I noticed that sometimes, it take a couple of seconds to get a response even though the service is a simple echo for now. So I'm wondering if establishing the connection is what takes the time, even though the server does HTTP/1.1 connection keep alive.
Should somehow reuse the client between requests or if it's ok to get a new one for every request?
This is my code. Should I keep locator and/or client around between requests or is it okay to forget it?
MyExampleServiceLocator locator = new MyExampleServiceLocator();
MyExampleServicePort client = locator.getMyExampleServicePort(url);
MyExampleRequest request = buildMyExampleRequest();
MyExampleResponse response = client.send(request); // This takes time sometimes

For complex services the cost of instantiating the locator may be high. Therefore you should always try to reuse it as much as possible. Locators are expected to be thread safe, so you can use them as singletons. Note however that in Axis 1.4 there is at least one thread safety issue regarding locators: AXIS-2498.
Creating a new stub (client) is less expensive, but reusing a stub is unproblematic. They are also expected to be thread safe (at least in Axis 1.4), except for scenarios that use the stub in a stateful way (e.g. HTTP sessions).
Axis' default HTTP transport only supports HTTP 1.0 and creates a new connection for every request.

problem with axis client stub timeout

I am writing an application which uses web services to connect a remote server.I have written a method to ping function to determine if the server is online or not(i.e. its providing the web services which can be accessed using host:port).I am executing a simple web service with a 2 sec timeout(available as an option in stub class before I make the call).Ideally the call should return within 2 seconds allowing me to ascertain whether the server is up or down.However in certain cases it takes far longer than 2 seconds.
Can anyone help me figure out why this is happening?Is there a way to ensure that the timeout value is honored ?
Thanks,
Fell

In Axis client stubs, there is an option for you to set the timeout. You can also use it. Note that the time-out is measured in milliseconds. check here
And if it is Axis2, you can use like this:
Stub s = new Stub();
ServiceClient sc = s.getServiceClient();
Options o = sc.getOptions();
o.setTimeOutInMilliSeconds(2000); //2 seconds
sc.setOptions(o);
s.setServiceClient(sc);
You can make your calls after setting the above stuff.

Don't use the default http sender, switch to commons http client based sender. Details are here - http://wiki.apache.org/ws/FrontPage/Axis/AxisCommonsHTTP - Same page has details on how to set various kinds of timeouts as well.