Synchronize data in mutiple laptop AngularJS - angularjs

I built an application and I host it in a local server. I would like When multiple users open the app and someone for example modify something, the modification will be applied for all the others automatically without refreshing the page.
I found a solution, that I call the function every 5 seconds for example, but when the number of users increase, it will make the request so slow sometimes. So I think it's not the better solution. Have you please any idea about this issue, what is the best solution for this problem?
Thanks.

You could look into long polling, which is an older way of handling this case. This would still have the performance/scalability issues you mentioned but works for simpler cases. More recently the websockets API exposes an easy way to get bidirectional communication between client and server with less overhead than polling.
A popular library for doing this nowadays is socket.io, which utilizes both long-polling and websockets and lets you easily handle things like disconnections and the like.

Related

Microservice, database relation and caching

I am new at microservices that is why these two question bothering me.
if we have per database per microservice, for example, we have a service called menu which maintains creating and updating menus and we have another service, for example user-access, which checks user's access to menu. This two services have their own database.
Which approach is right? Calling menu service from user-access, or caching menus to Redis and calling requested menus from Redis? And what if i need to return menu name to front-end from user-access application.
Thank you for your answer in advance.
Microservice architecture may sound interesting on paper but is a lot more than that when it comes to implementing it.
Many developers face queries just like yours all the time, i.e about choosing the right pattern or flow of API calls.
I think the most simple and straight forward answer to this is that you should decide what is the correct approach depending on your applications needs. One may find your approach wrong or inefficient even though it may be perfect for you. At the end, it all depends on what happens when the application scales. How your approach reacts to the growing traffic and then only you get to know the power and importance of microservice architecture.

ReactJS poll database or receive data being pushed from server

I am having a hard time deciding on how to best implement what I thought would be a simple scenario. I need to either have React poll a database or API(which seems like an in-efficient solution) or be able to "push" data from another server into a react application.
Websockets seems to be able to solve this. But to me it seems very complicated to solve something that cannot be that unique of a problem. The backend server will be a ASP.Net WebAPI and I can easily have that polling the database and therefore only dispatch/call when something needs to reach the React app. But I cannot seem to find simple implementations of this in React? Perhaps it is just my search skills that are lacking, so perhaps just pointing me in directions on what to search for would be helpful.

Silverlight Multi-User application with synchronization

I am wondering if it's possible to create a graphical application in Silverlight which supports synchronisation between the different clients.
To be a bit more precise, I am drawing concepts of developing a Silverlight Game. Visitors would log-in, and see live, synchronised what the other vistors are doing.
If it is possible to have this implemented, I would like to know what is needed to create a fully synched Silverlight environment between multiple peers. Anything from links, code snippets, ideas and / or alternatives are more than appreciated !
Please do not suggest Flash, as I do not own a valid Flash building license, I prefer to have this created within Visual Studio 2010.
Edit:
I want it to be as lightweight for the clients as possible, I don't care much for the server, and also low bandwidth consuming. I don't know whether a broadcasting principal is the only option to have all the events taken place at the same time?
You may want to take a look at the Polling Duplex protocol of WCF. This is the subscription and publish concept. Support in SL has been about since version 2 so there's plenty of articles out there. An article I referenced for a message broadcast system we put in place at work can be found here...
http://tomasz.janczuk.org/2009/07/pubsub-sample-using-http-polling-duplex.html
which also mentions an interesting project on codeplex (I've not used)...
http://laharsub.codeplex.com/
A simple and working (but rather inefficient) solution would be for all clients to ask a WCF/Ria service on the server for status updates in regular intervals, perhaps once every X seconds or so, letting the server keep track of changes relevant to the calling clients.

Calls to webservice are slow, should i be using something else?

Currently we got a web service up and running that handles all our C.R.U.D calls to our database, and pretty much every interaction between user and the database.
(starting with checking the database to see if there's an update for the particular version of the end users application, checking credentials, checking/reading various other application settings, etc, etc)
Pretty much everything our desktop application does (written in c# with WPF .net framework 3.5) it makes a call to the web service. Problem is that on slower machines this takes way too long. Some of users have to wait up to 3 minutes for the app to cold start (this is probably partly because of .net frameworks slow load time...but the web service calls don't help anything).
I guess since our applications are more or less a fancy front end to a database (SQL SERVER 2005), should we be using something else to communicate with it besides a web service? What else is there? I choose the web service because it's the only thing I knew how to do. (besides connecting directly to the database) What do other similar apps use?
Thank You
As mentioned by #Chris Marisic, first profile to ensure that the problem is in the web called. Assuming that it is, there are a few things you can try (I don't know WPF so you will have to see how they work with the framework).
Batch similar items.
For example instead of loading 1 row at a time from table (or equivalent), load several.
May web calls asynchronous.
If you have to send out a bunch of independent calls to the web service, send them asynchronously so that multiple requests are going across the network at once.
Cache values. This can add a lot of complexity if you are not careful (depending on how much you care if the cache is up to date). The ability to listen to the server for changes (or the ability to have the server push changes) makes this one easier to handle.
I had a similar problem on a different framework and I got quite a bit of speedup just with #1.
Profile Profile Profile. Don't make assumptions.
By "web service" do you mean "SOAP service"? Profiling will tell you whether or not SOAP is buying you something.
It's likely that latency and (n+1) query is killing you. It should be easy to measure.

What are the cons of a web based application

I am going to write a database application for the camp I work for. I am thinking about writing it in C# with a Windows GUI interface but using a browser as the application is seeming more and more appelaing for various reasons. What I am wondering is why someone would not choose to write an application as a web application. Ex. The back button can cause you some trouble. Are there other things that ayone can think of?
There are plenty of cons:
Speed and responsiveness tend to be significantly worse
Complicated UI widgets (such as tree controls) are harder to do
Rendering graphics of any kind is pretty tricky, 3D graphics is even harder
You have to mess around with logins
A centralised server means clients always need network access
Security restrictions may cause you trouble
Browser incompatibilities can cause a lot of extra work
UI conventions are less well-defined on the web - users may find it harder to use
Client-side storage is limited
The question is.. do enough of those apply to your project to make web the wrong choice?
One thing that was not mentioned here is the level of complexity and knowledge required to generate a good web application. The problem being unless you are doing something very simple, there is no "Single" knowledge or technology that goes into these applications.
For example if you were to write an application for some client server platform.. you may develop in Java or C++. For a complex web application you may have to have expertise in Java, Java Script, HTML, Flash, CSS, Ajax, SQL, J2EE.. etc. Also the components of a web based application are also more numerous, Web Application Server, HTTP Server, Database, Browser.. are tipical components but there could be more.. a client server app is tipical just what it says.. a client application and a Server application. My experience and personal preference is not web based .. web based is great for many things. But even though I am an IT Architect for a leading company that is completely emersed in Web Apps as the solution for everything... The cons are many still.. I do thing the technology will evolve and the cons will go away over time though.
Essentially the real limitations are only through of the platform, being the browser. If you have to account for all browsers in current use that can be a pain due to varying degrees of standards in each of them.
If have control of the which browser to use, that is everyone is on computers that you control on site, and say you install firefox on all of them, you could then leverage the latest Javascript and CSS standards to their fullest in your content delivery.
[edit] You could also look into options like the adobe integrated runtime or "AIR" as an option allowing you to code the front-end with traditional browser based options like xhtml/css/javascript, flash/flex and have the backend hooked up to your database online, only also providing functionality of a traditional desktop app at the same time.
The biggest difference and drawback I see with web applications is state management. Since the web is, by nature, stateless every thing you want to maintain has to be sent back and forth from the server with every request and response. How to efficiently store and retrieve it in a matter with respect to page size and performance is hard to do at times. Also the fact that there is no real standard (at least not that everyone adheres to) for browsers makes consistency really..........fun.
You need to have a network access to the server that you are going to have the web application on (if there are going to be multiple users for the application - which is typically the case).
Actually, there are more pros than cons - if you can give some details about your application, we could help a little more...
It completely depends on the requirements of your project. For the most part, there isn't much web applications cannot do these days. Admittedly, certain applications do belong on the desktop as browsers (while currently advancing, and rapidly), still are not quite there yet. From the advent of applications such as Google Docs, Gmail
There isn't much you -cannot- do on the web. If you're creating a World of Warcraft competitor however, the web is most certainly not the optimal solution. Again, unfortunately we'd need more insight on the application you're building for the camp. The best part about the web is that anyone with a browser can use your application.
Web applications delegate processing to a remote machine. Depending on the amount of processing, this can be a con. Consider a photo editor that's a web app.
Web applications also can't deal with a whole lot of data going back and forth to and from a client. You can watch video online.. when it's compressed. It will be awhile before we see any web-based video editing software.
Browser compatibility is also a hassle. You can't control the look-and-feel of the application 100%.
Vaibhav has a good point. What's your application?
A major one is down time for migrations... users will not expect the application to be down, ever, but realistically it will have to be down for major upgrades. When doing this with a desktop application, the user (or end-user systems admin) is in control of when upgrades happen; with an online app, they're not.
For applications which have large data, performance can be a major problem as you're storing a large number of users' data centrally, which means the IO performance will not be as good as it would be if you gave them all a laptop.
In general scalability gives problems for a server-based app. Desktop applications scale really well.
You can do an awful lot with a web-based app, but it is a lot easier to do certain things with a thick client:
Performance: You get simple access to the full power of the client's CPU.
Responsiveness: Interactivity is fast and easy.
Graphics: You can easily use graphics libraries such as DirectX and OpenGL to create fast impressive graphics.
Work with local files
Peer-to-peer
Deciding whether a web application is a good approach depends on what you are trying to achieve. However here are some more general cons of web applications:
Real integration with desktop apps (e.g. Outlook) is impossible
Drag and drop between your app and the desktop / other running apps
With a web application, there are more privacy concerns, when you are storing user data on your servers. You have to make sure that you don't loose/disclose it and your users have to be comfortable with the idea of storing that data on your servers.
Apart from that, there are many security problems, like Man-in-the-middle attacks, XSS or SQL injections.
You also need to make sure that you have enough computing power and bandwidth at hand.
"Ex. The back button can cause you some trouble."
You'll have to be specific on this. A lot of people make fundamental mistakes in their web applications and introduce bugs in how they handle transactions. If you do not use "Redirect after Post" (also known as Post-Redirect-Get, PRG design), then you've created a bug which appears as a problem with the back button.
A blanket statement that the back button in trouble is unlikely to be true. A specific example would clarify your specific question on this.
The back button really is not that much of an issue if you design your application correctly. You can use AJAX to manipulate parts of the current page, without adding items into the browser history (since the page itself wont change).
The biggest issue with designing web applications has to do with state, and the challenges that need to be programmed around. With a desktop application, state is easy to handle, you can leave a database connection opened, lock the record and wait for the user to make the changes and commit. With a web application, you could lock the record...but then what if the user closes the browser? These things must be overcome in the design of your application.
When designing a web application, make sure that each trip to the server "stands alone" and provides a complete answer. Always re-initialize your variables before performing any work and never assume anything. One of the challenges I ran into once was pulling "pages" of grid data back to the user. In a real busy system, with record additions/modifications happening in real time, the user navigation from page to page would vary greatly, sometimes even resulting in viewing the same set of a few records as new additions were added in-front of the query.

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