Is MQ publish/subscribe domain-specific interface generally faster than point-to-point?_问答_开发者

I'm working on the existing application that uses transport layer with point-to-point MQ communication.

For each of the given list of accounts we need to retrieve some information.

Currently we have something like this to communicate with MQ:

responseObject getInfo(requestObject){
    code to send message to MQ
    code to retrieve message from MQ
}

As you can see we wait until it finishes completely before proceeding to the next account. Due to performance issues we need to rework it.

There are 2 possible scenarios that I can think off at the moment.

1) Within an application to create a bunch of threads that would execute transport adapter for each account. Then get data from each task. I pr开发者_运维问答efer this method, but some of the team members argue that transport layer is a better place for such change and we should place extra load on MQ instead of our application.

2) Rework transport layer to use publish/subscribe model. Ideally I want something like this:

void send (requestObject){
  code to send message to MQ
}

responseObject receive()
{
  code to retrieve message from MQ
}

Then I will just send requests in the loop, and later retrieve data in the loop. The idea is that while first request is being processed by the back end system we don't have to wait for the response, but instead send next request.

My question, is it going to be a lot faster than current sequential retrieval?

The question title frames this as a choice between P2P and pub/sub but the question body frames it as a choice between threaded and pipelined processing. These are two completely different things.

Either code snippet provided could just as easily use P2P or pub/sub to put and get messages. The decision should not be based on speed but rather whether the interface in question requires a single message to be delivered to multiple receivers. If the answer is no then you probably want to stick with point-to-point, regardless of your application's threading model.

And, incidentally, the answer to the question posed in the title is "no." When you use the point-to-point model your messages resolve immediately to a destination or transmit queue and WebSphere MQ routes them from there. With pub/sub your message is handed off to an internal broker process that resolves zero to many possible destinations. Only after this step does the published message get put on a queue where, for the remainder of it's journey, it then is handled like any other point-to-point message. Although pub/sub is not normally noticeably slower than point-to-point the code path is longer and therefore, all other things being equal, it will add a bit more latency.

The other part of the question is about parallelism. You proposed either spinning up many threads or breaking the app up so that requests and replies are handled separately. A third option is to have multiple application instances running. You can combine any or all of these in your design. For example, you can spin up multiple request threads and multiple reply threads and then have application instances processing against multiple queue managers.

The key to this question is whether the messages have affinity to each other, to order dependencies or to the application instance or thread which created them. For example, if I am responding to an HTTP request with a request/reply then the thread attached to the HTTP session probably needs to be the one to receive the reply. But if the reply is truly asynchronous and all I need to do is update a database with the response data then having separate request and reply threads is helpful.

In either case, the ability to dynamically spin up or down the number of instances is helpful in managing peak workloads. If this is accomplished with threading alone then your performance scalability is bound to the upper limit of a single server. If this is accomplished by spinning up new application instances on the same or different server/QMgr then you get both scalability and workload balancing.

Please see the following article for more thoughts on these subjects: Mission:Messaging: Migration, failover, and scaling in a WebSphere MQ cluster

Also, go to the WebSphere MQ SupportPacs page and look for the Performance SupportPac for your platform and WMQ version. These are the ones with names beginning with MP**. These will show you the performance characteristics as the number of connected application instances varies.

It doesn't sound like you're thinking about this the right way. Regardless of the model you use (point-to-point or publish/subscribe), if your performance is bounded by a slow back-end system, neither will help speed up the process. If, however, you could theoretically issue more than one request at a time against the back-end system and expect to see a speed up, then you still don't really care if you do point-to-point or publish/subscribe. What you really care about is synchronous vs. asynchronous.

Your current approach for retrieving the data is clearly synchronous: you send the request message, and wait for the corresponding response message. You could do your communication asynchronously if you simply sent all the request messages in a row (perhaps in a loop) in one method, and then had a separate method (preferably on a different thread) monitoring the incoming topic for responses. This would ensure that your code would no longer block on individual requests. (This roughly corresponds to option 2, though without pub/sub.)

I think option 1 could get pretty unwieldly, depending on how many requests you actually have to make, though it, too, could be implemented without switching to a pub/sub channel.

The reworked approach will use fewer threads. Whether that makes the application faster depends on whether the overhead of managing a lot of threads is currently slowing you down. If you have fewer than 1000 threads (this is a very, very rough order-of-magnitude estimate!), i would guess it probably isn't. If you have more than that, it might well be.