I am sending small messages consisting of xml(about 1-2 KB each) across the internet from a windows application to a asp.net web service.
99% of the time this works fine but sometimes a message will take an inordinate amount of time to arive, 25 - 30 seconds instead of the usual 4 - 5 seconds. This delay also causes the message to arrive out of sequence.
Is there anyway i can solve this issue so that all the messages arrive quickly and in squence or is that not possible to gurantee when using a web service in this manner ?
If its not possible to resolve can i please get recomendations of a low latency messaging framework that can deliver messages in order over the internet.
Thanks.
Is there anyway i can solve this issue so that all the messages arrive quickly and in squence or is that not possible to gurantee when using a web service in this manner ?
Using just webservices this is not possible. You will always run into situations where occasionally something will take much longer that it "should". This is the nature of network programming and you have to work around it.
I would also recommend using XMPP for something like this. Have a look at xmpp.org for info on the standard and jabber-net for a set of client libraries for .Net.
Well this is a little off target, but have you looking into the XMPP (Jabber) protocol.
It's the messaging system that GTalk uses. Quite simple to use. Only downside to it, is that you will need a stateful service to receive and process the messages.
I also agree with #Mat's comment. It was the first solution that came to mind, then i remembered that I used XMPP in the pas to acomplish fast/ small and reliable messages between servers.
http://xmpp.org/about-xmpp/
if you search google you will easily find .net libraries which support this protocol.
and there are plenty of free jabber servers out there.
One way to ensure your messages are sent in sequence and are resolved as a batch together is to make one call to the webservice with all messages that are dependent on each other as a single batch.
Traditionally, when you make a call to a web service you do not expect that other calls to the web service will occur in a specific order. It sounds like you have an implicit sequence the data needs to arrive in the destination application, which makes me think you need to group your messages together and send them together to ensure that order.
No matter the speed of the messaging framework, you cannot guarantee to prevent a race condition that could send messages out of order, unless you send one message that has your data in the correct order.
If you are sending messages in a sequence across internet, you will never know how long will take the message to arrive from one point to another. One possible solution is to include in each message its position in the sequence, and in each endpoint implement the logic to order the messages prior to processing them. If you receive a message out of sequence, you can wait for the missing message, or request to the other endpoint to resend it.
Related
I want to fetch the data of a stock. Since the data changes very fast, is there any way to pull the data like 50-100 times a second from trading websites?
And can we implement that using a raspberry Pi 4 8gig model.
RasPi4 should be more than adequate for this task. Both the ethernet and WiFi hardware is capable of connections at these speeds. (Unless you’re running a bunch of other stuff on it.) Consider where your bottlenecks may be, likely ISP or other network traffic). Consider avoiding WiFi in favor of cat5e or cat6. Consider hanging this device off your router (edge) to keep lan traffic lower and consider QOS settings if you think this traffic may compete with other lan traffic.
This appears to be a general question with no specific platform in mind. For stocks, there are lots of platforms to choose from.
APIs for trading platforms often include a method to open a stream. Instead of a full TCP conversation for each price check, a stream tells the server to just keep on sending data. There are timeout mechanisms of course, but it is good to close that stream gracefully (It’s polite since you’re consuming server resources at a different scale. I’ve seen some financial APIs monitor and throttle stream subscribers who leave sessions open.).
For some APIs/languages you can find solid classes already built on GitHub. Although, if simply pulling and reading a stream then the platform API doc code snippets should be enough to get you going.
Be sure to find out what other overhead may be implicated. For example, if an account or API key is needed to open a stream then either a session must be opened first or the creds must be passed with the stream being opened. The API docs will say. If you’re new to this sort of thing, just be a detective and try to infer what is needed. API docs usually try to be precise and technically correct with the absolute minimum word count.
Simply checking the steam should be easy. Depending on how that steam can be handled by your code/script, it may be harder to perform logic on the stream while it is being updated. That’s usually a thread issue or a variable scope issue depending on the script/code. For what you’re doing I would consider Python or PowerShell depending on your skill-set and other design parameters.
I discovered Rebus contains FileSystemMessageQueue. It seems too great to be true so I wanted to ask few questions about it :)
Is it thread-safe/process-safe
Is it transactional
Why it uses JSON as serialization format (doesn't it add limitations to POCOs in comparison to binary serializer?)
Could it work as separate without bus? (just as separate dll, not service)
For small amount of messages, could it be replacement of MSMQ? I mean how it could be compared to MSMQ if we speak about local (not-networked), not resource-intensive messaging? would it be as good as MSMQ?
Thanks in advance
The FileSystemMessageQueue started out as a fun experiment because I wanted to use Dropbox as a transport - which actually seems to work, but I have not tested it in any way, except from making the transport pass Rebus' usual transport contract tests and show it off at a couple of user group meetings and such :)
Therefore: Please understand that you'll be the one testing the transport, and if you do use it you'll almost immediately be the one in the world with the most experience in using it :)
</disclamer>
1) The transport keeps track of which message files are currently being handled to ensure that the same file is not being received twice, so you can safely have multiple threads receiving messages in the same endpoint.
You cannot have do competing consumers though, because there's currently no locking that can span multiple processes (could probably be done though, by using the OS to lock the files and keep the file handle for the time it takes to handle the message).
2) No. It satisfies the same at-least-once delivery guarantee as all the other transports in Rebus, but it is not transactional and it is not capable of committing its work atomically.
I've made the transport postpone the actual writing of the outgoing messages to the point after you've done your own work in your message handler, so messages won't be visible to recipients too soon - but in theory you could run into a situation where a bunch of outgoing messages were sent, and then the deletion of the received message file fails, which will result in receiving the same message again - that's why it's called "at least once" ;)
3) It uses JSON because that's an easy way to write an object to a file (even though the actual message body is serialized and encoded using the configured serializer).
4) ??? I don't understand your question :)
5) Yes and no - I guess that it would be just as good as MSMQ if we speak about local and not resource intensive messages.
I haven't performed any load tests, but I'm guessing it will be much slower than MSMQ regarding message volume. I do think that it is capable of transferring messages that are much much bigger than MSMQ though, because MSMQ still has (to my knowledge) a hard upper cap of 4 MB per message.
Part of this question is I'm not even sure what exactly I'll need to ask, so I'll start with the situation and work out from there.
One project I'm working on involves use of COMET via the aspComet library. The use case of the program is somewhat of a collaborative slideshow. One person runs the bulk of it, with one or more participants able to perform certain actions. Low latency between when an action is performed on screen
Previously, it was just running on one server. Now, we're wanting to scale it out a bit, more for reliability than performance reasons. So, we have some boxes out in Rackspace's cloud and all that fun stuff.
I knew from the start of this that I was going to need to make some changes to the way the COMET stuff works since different people in the same "show" might be on different servers, and I have no way of knowing what "show" they belong to until after they have already arrived on the site.
I initially tackled this using the WCF Mesh provider, which wasn't well documented to start with, now I'm running into issues with dispatching messages to it sometimes get lost, or delayed (I'm not 100% sure what is going on there), but it screws up the long poll for COMET and breaks things in rather strange ways (Clicking a button may trigger an event, or it'll hang for 10 seconds {long poll duration} and not actually do anything).
More research leads me to believe one of the .Net service bus providers may do what I need. However, I can't find examples that would cover what I need:
No single point of failure (outside of a database)
No hardcoding of peers.
Near-realtime (no polling, event based would be best)
My ideal solution would involve that when a server comes up, it lets other servers know of its existence (Even if it's just a row in a table somewhere), and they can start sending broadcast messages among each other, with each server being both a publisher and subscriber. This is what I somewhat had in the WCF Mesh provider, but I'm not overly confident in that code.
Can anyone point me in the right direction with this? Even proper terms to look for in the docs for service bus providers would be good at this point. Or are service buses not what I want? At this point I would settle for setting up a Jabber server on each web server and use that, if it could fit within my constraints.
I can't speak a ton to NServiceBus, but I expect the answers will be similar.
Single point of failure: MSMQ can use multicasting, which means each endpoint will broadcast it's existence and no DB table is needed. RabbitMQ uses this Exchange-to-Queue binding process which means as long as the Rabbit instance or cluster is up then messages still exist. RabbitMQ can be clustered, MSMQ cannot be. *Note: You might have issues with multicasting with Rackspace, no idea how they work. If so, you'll have to fall back on the runtime services for MSMQ (not RabbitMQ), that would create a single point of failure because everyone has a single point to coordinate control messages through.
Hard coding of peers: discussed above a bit; MSMQ's multicast handles it. Rabbit it can also be done, just bind queues to an exchange you want to listen to. MassTransit takes care of this for you.
Near-realtime: These both use messaging which is near real time. There's no polling in your message consumer code.
I think a service bus seems like a reasonable solution for what you're trying. Some more details would likely be needed, but the general messaging approach is correct. There are other more light weight messaging libraries if you decided you just want something on top of RabbitMQ and configure Rabbit to handle most of the stuff.
To get started with MassTransit, we have documentation up: http://readthedocs.org/projects/masstransit/ and mailing list http://groups.google.com/group/masstransit-discuss. Join the mailing list if you have future questions and someone will try and help you out.
Does anyone have experiance in a lot of these?
I'm not so intrested in the pdf creation part of LCDS.
Just for flex messaging which would give me the best performance? As far as I know LCDS and WebOrb both do real time streaming is that correct?
Basically the question is which gives quickest response and which will allow for most client connected to a single servlet container.
Thanks
Edit 1
This may be clearer what I want. I'm looking to server at least 5000 clients with sub second response times with push messages, I'm trying to figure out which is the most scalable option, I've been quoted several million push messages a day. Obviously we can throw more servers at the problem I'm not convinced thats the most maintainable option.
Its not media streaming I'm looking for, but more event updates. It must work without sticky sessions.
LiveCycleDS & WebOrb are the only ones providing messaging using sockets through RTMP protocol. Note that in this case the clients are not connected to a servlet container, but to a dedicated server included in the product distribution (bypassing the servlet mechanism).
There are more messaging servers on the market, Lightstreamer is one of them. Or Flash media server.
There are many more things to be taken into consideration when choosing a solution however (price, integration with various architectures (like DMZ) and frameworks, paid support, documentation, your relation with the sales representative etc).
Even on big-time sites such as Google, I sometimes make a request and the browser just sits there. The hourglass will turn indefinitely until I click again, after which I get a response instantly. So, the response or request is simply getting lost on the internet.
As a developer of ASP.NET web applications, is there any way for me to mitigate this problem, so that users of the sites I develop do not experience this issue? If there is, it seems like Google would do it. Still, I'm hopeful there is a solution.
Edit: I can verify, for our web applications, that every request actually reaching the server is served in a few seconds even in the absolute worst case (e.g. a complex report). I have an email notification sent out if a server ever takes more than 4 seconds to process a request, or if it fails to process a request, and have not received that email in 30 days.
It's possible that a request made from the client took a particular path which happened to not work at that particular moment. These are unavoidable - they're simply a result of the internet, which is built upon unstable components and which TCP manages to ensure a certain kind of guarantee for.
Like someone else said - make sure when a request hits your server, you'll be ready to reply. Everything else is out of your hands.
They get lost because the internet is a big place and sometimes packets get dropped or servers get overloaded. To give your users the best experience make sure you have plenty of hardware, robust software, and a very good network connection.
You cannot control the pipe from the client all the way to your server. There could be network connectivity issues anywhere along the pipeline, including from your PC to your ISP's router which is a likely place to look first.
The bottom line is if you are having issues bringing Google.com up in your browser then you are guaranteed to have the same issue with your own web application at least as often.
That's not to say an ASP application cannot generate the same sort of downtime experience completely on it's own... Test often and code defensively are the key phrases to keep in mind.
Let's not forget browser bugs. They aren't nearly perfect applications themselves...
This problem/situation isn't only ASP related, but it covers the whole concept of keeping your apps up and its called informally the "5 nines" or "99.999% availability".
The wikipedia article is here
If you lookup the 5 nines you'll find tons of useful information, which you can apply as needed to your apps.