I've got a backend to be implemented in Python that should stream data to a web browser where the JavaScript is creating the representation (e.g. continuously updating a variable or drawing to a <canvas>).
That data will update at a rate of up to 100 Hz (and might as a worst case scenario even be at 1000 Hz...) with perhaps 10 - 20 Bytes each.
So my first thought of using the COMET pattern would produce far too much overhead, I guess.
My next guess were WebSockets. They would be a perfect fit - but being disabled in Firefox makes them unusable for me.
So what is your recommendation to use in this case?
(Requirement: running in a few modern browsers on pure JavaScript, no Flash or Java allowed. Back end in Python. Already used lib is jQuery. Implementation should be easy, preferably using lightweight libs)
The solution I took now is to use the COMET pattern and transport all data that queued up in the backend since the last request. So I'm not polling during times of slow data generation (-> COMET) and I'll only have that amount of connections that the frontend (i.e. the browser) can handle as it's creating them.
And the overhead is reduced as each request contains a few data points. (You could even say that the overhead is scaled dynamically depending on the data rate. As the data rate gets higher, the overhead sinks...)
As an update to this question, nowadays, you should be able to use Server-sent events. I didn't use XHR due to it keeping the entire response in memory, and didn't use websockets, since I didn't need duplex comms. I had pretty much the same question, answered it here:
How to process streaming HTTP GET data?
Related
Let's say we have the page. During rendering the page, we need to execute about 15 requests to API for getting some data.
How does this number of requests will affect on performance for desktop/mobile versions? Do I need to do any changes for reducing the number of requests? It will be great if you can send me the link with clarification related to this theme.
Optimization is this case really depends on the result of the API calls. Like what you are getting in response. Is the same static data each time or is it the same data with slight changes or is it extremely weird data which changes in real time?
There are many optimization techniques like whether to use Sync or Async, caching, batching, payload reduction. There could be many more but I know the few above. You can get a lot about these with a single Google query. It is up to you to decide which to use and where to use.
Various browsers have various limits for maximum connections per host
name; you can find the exact numbers at
http://www.browserscope.org/?category=network
Here is an interesting article about connection limitations from web
performance expert Steve Souders
http://www.stevesouders.com/blog/2008/03/20/roundup-on-parallel-connections/
12 requests to one domain/service is not much. latest versions of browsers supports around 6 simultaneous http 1.x connections per domain. So that means, your first 6 service calls (to a particular domain) needs to be done before initiating the next HTTP connection to that domain. (With HTTP2, this limitation will not be there though). So if your application is not intended to be high performing you are usually fine.
On the other hand, if every milli seconds counts, then it's better to have an edge service / GraphQL (my preference) aggregates all the services and send to the browser.
I'm trying to do some processing with webworker on image data from canvas. Solution, that I have right know, works quite ok, but there are still some visible lags when I do the processing (because besides processing I have to draw video from webcam to canvas and it starts to lag).
So I tried to use webworker and I did everything asynchronously. The only problem is that when I use JSON.stringify, it takes longer than actual processing.
My question: is there any other way, how to pass lot of data via worker.postMessage quickly? Is there some kind of workaround that I don't know about?
Small subquestion: what for are webworkers? I find workers really useless, passing just strings.
EDIT:
possible duplicate: Pass large amounts of data between web worker and main thread
Everything is copied to a webworker, so unless your computation is very intensive, I doubt you'll see much gain there.
WebWorkers are meant for long-running, computationally intensive algorithms. The obvious use cases are:
AI in web games
Raytracers
Compression/decompression on large data sets
AJAX requests that need a lot of processing before it's displayed
Other complex algorithms
Since data is copied both ways, you have to be careful about what you're doing. WebWorkers don't have access to the DOM, so they're likely useless for what you're trying to do. I don't know what your app does, but it sounds like it isn't very intense.
There are also Sharedworkers, which can be shared by multiple tabs/windows, which is a really nice way to pass data between tabs.
Edit:
Also look into the structured clone algorithm. It seems to be more efficient that JSON for many things, and can even duplicate ImageData (so it doesn't just support strings anymore).
For browsers that don't support the clone algorithm, I would urge you to consider base64. It's decent at storing binary data, and I think it's faster than JSON.stringify. You may have to write some code to handle it though.
looking for some general advice and/or thoughts...
i'm creating what i think to be more of a web application then web page, because i intend it to be like a gmail app where you would leave the page open all day long while getting updates "pushed" to the page (for the interested i'm using the comet programming technique). i've never created a web page before that was so rich in ajax and javascript (i am now a huge fan of jquery). because of this, time and time again when i'm implementing a new feature that requires a dynamic change in the UI that the server needs to know about, i am faced with the same question:
1) should i do all the processing on the client in javascript and post back as little as possible via ajax
or
2) should i post a request to the server via ajax, have the server do all the processing and then send back the new html. then on the ajax response i do a simple assignment with the new HTML
i have been inclined to always follow #1. this web app i imagine may get pretty chatty with all the ajax requests. my thought is minimize as much as possible the size of the requests and responses, and rely on the continuously improving javascript engines to do as much of the processing and UI updates as possible. i've discovered with jquery i can do so much on the client side that i wouldn't have been able to do very easily before. my javascript code is actually much bigger and more complex than my serverside code. there are also simple calulcations i need to perform and i've pushed that on the client side, too.
i guess the main question i have is, should we ALWAYS strive for client side processing over server side processing whenever possible? i 've always felt the less the server has to handle the better for scalability/performance. let the power of the client's processor do all the hard work (if possible).
thoughts?
There are several considerations when deciding if new HTML fragments created by an ajax request should be constructed on the server or client side. Some things to consider:
Performance. The work your server has to do is what you should be concerned with. By doing more of the processing on the client side, you reduce the amount of work the server does, and speed things up. If the server can send a small bit of JSON instead of giant HTML fragment, for example, it'd be much more efficient to let the client do it. In situations where it's a small amount of data being sent either way, the difference is probably negligible.
Readability. The disadvantage to generating markup in your JavaScript is that it's much harder to read and maintain the code. Embedding HTML in quoted strings is nasty to look at in a text editor with syntax coloring set to JavaScript and makes for more difficult editing.
Separation of data, presentation, and behavior. Along the lines of readability, having HTML fragments in your JavaScript doesn't make much sense for code organization. HTML templates should handle the markup and JavaScript should be left alone to handle the behavior of your application. The contents of an HTML fragment being inserted into a page is not relevant to your JavaScript code, just the fact that it's being inserted, where, and when.
I tend to lean more toward returning HTML fragments from the server when dealing with ajax responses, for the readability and code organization reasons I mention above. Of course, it all depends on how your application works, how processing intensive the ajax responses are, and how much traffic the app is getting. If the server is having to do significant work in generating these responses and is causing a bottleneck, then it may be more important to push the work to the client and forego other considerations.
I'm currently working on a pretty computationally-heavy application right now and I'm rendering almost all of it on the client-side. I don't know exactly what your application is going to be doing (more details would be great), but I'd say your application could probably do the same. Just make sure all of your security- and database-related code lies on the server-side, because not doing so will open security holes in your application. Here are some general guidelines that I follow:
Don't ever rely on the user having a super-fast browser or computer. Some people are using Internet Explore 7 on old machines, and if it's too slow for them, you're going to lose a lot of potential customers. Test on as many different browsers and machines as possible.
Any time you have some code that could potentially slow down or freeze the browser momentarily, show a feedback mechanism (in most cases a simple "Loading" message will do) to tell the user that something is indeed going on, and the browser didn't just randomly freeze.
Try to load as much as you can during initialization and cache everything. In my application, I'm doing something similar to Gmail: show a loading bar, load up everything that the application will ever need, and then give the user a smooth experience from there on out. Yes, they're going to have to potentially wait a couple seconds for it to load, but after that there should be no problems.
Minimize DOM manipulation. Raw number-crunching JavaScript performance might be "fast enough", but access to the DOM is still slow. Avoid creating and destroying elements; instead simply hide them if you don't need them at the moment.
I recently ran into the same problem and decided to go with browser side processing, everything worked great in FF and IE8 and IE8 in 7 mode, but then... our client, using Internet Explorer 7 ran into problems, the application would freeze up and a script timeout box would appear, I had put too much work into the solution to throw it away so I ended up spending an hour or so optimizing the script and adding setTimeout wherever possible.
My suggestions?
If possible, keep non-critical calculations client side.
To keep data transfers low, use JSON and let the client side sort out the HTML.
Test your script using the lowest common denominator.
If needed use the profiling feature in FireBug. Corollary: use the uncompressed (development) version of jQuery.
I agree with you. Push as much as possible to users, but not too much. If your app slows or even worse crashes their browser you loose.
My advice is to actually test how you application acts when turned on for all day. Check that there are no memory leaks. Check that there isn't a ajax request created every half of second after working with application for a while (timers in JS can be a pain sometime).
Apart from that never perform user input validation with javascript. Always duplicate it on server.
Edit
Use jquery live binding. It will save you a lot of time when rebinding generated content and will make your architecture more clear. Sadly when I was developing with jQuery it wasn't available yet; we used other tools with same effect.
In past I also had a problem when one page part generation using ajax depends on other part generation. Generating first part first and second part second will make your page slower as expected. Plan this in front. Develop a pages so that they already have all content when opened.
Also (regarding simple pages too), keep number of referenced files on one server low. Join javascript and css libraries into one file on server side. Keep images on separate host, better separate hosts (creating just a third level domain will do too). Though this is worth it only on production; it will make development process more difficult.
Of course it depends on the data, but a majority of the time if you can push it client side, do. Make the client do more of the processing and use less bandwidth. (Again this depends on the data, you can get into cases that you have to send more data across to do it client side).
Some stuff like security checks should always be done on the server. If you have a computation that takes a lot of data and produces less data, also put it on the server.
Incidentally, did you know you could run Javascript on the server side, rendering templates and hitting databases? Check out the CommonJS ecosystem.
There could also be cross-browser support issues. If you're using a cross-browser, client-side library (eg JQuery) and it can handle all the processing you need then you can let the library take care of it. Generating cross-browser HTML server-side can be harder (tends to be more manual), depending on the complexity of the markup.
this is possible, but with the heavy intial page load && heavy use of caching. take gmail as an example
On initial page load, it downloads most of the js files it needed to run. And most of all cached.
dont over use of images and graphics.
Load all the data need to show in intial load and along with the subsequent predictable user data. in gmail & latest yahoo mail the inbox is not only populated with the single mail conversation body, It loads first few full email messages in advance at the time of pageload. secret of high resposiveness comes with the cost (gmail asks to load the light version if the bandwidth is low.i bet most of us have experienced ).
follow KISS principle. means keep ur desgin simple.
And never try to render the whole page using javascript in any case, you cannot predict all your endusers using the high config systems or high bandwidth systems.
Its smart to split the workload between your server and client.
If you think in the future you might want to create an API for your application (communicating with iPhone or android apps, letting other sites integrate with yours,) your would have to duplicate a bunch of code for all those devices if you go with a bare-bones server implementation of your application.
I have written pure JavaScript front ends before and started noticing performance decrease when working with large stores of data. I have tried using xml and json, but in both cases, it was a lot for the browser to handle.
That poses my question, which is how much is too much?
You can't know, not exactly and not always. You can make a good guess.
It depends on the browser, OS, RAM, CPU, what else is running at that moment, how fast their connection is, what else they're transferring, etc.
Figure out several situations you expect for your average user, and test those. Add for various best, worst, and interesting (e.g. mobile, tablet) cases.
You can, of course, apply experience and extrapolate from your specific cases, and the answer will change for the future.
But don't fall into the trap of "it works for me!"
I commonly see this with screen resolutions: as those have increased, it's much more popular to have multiple windows visible at the same time. In 1995 it was rare for me to not have something maximized; now fifteen years later, it's exactly the opposite.
Yet sometimes people will design some software or a website, use lower contrast[1], maximize it, and connect to a server on localhost—and that's the only evaluation they do.
[1] Because they know what the text says and don't need to read it themselves, so lower contrast looks aesthetically better.
In my opinion, if you need to stop and think about this issue, then the data is too much. In general you should design your applications so that users with a low-end netbooks and/or slow internet connections are still able to run them. Also keep in my mind that more often than not your application isn't the only page your users are visiting at the same time.
My recommendation is to use Firefox with Firebug to do some measurements. See how long a request takes to complete in a modest configuration. If it takes noticeable time for the browser to render data, then you'd better off doing a redesign.
A good guiding principle should be that instead of worrying about whether the browser can handle the volume of data you're sending it, worry about whether your user can handle it. It all depends on the presentation of course (i.e., a lot of data bound for a visualization tool that'll render a complex graph in a canvas is different than a lot of raw numbers bound for a gigantic table), but in my experience a user's brain reaches data overload before the browser/network/client computer.
It really depends on the form that your external data is going to take in your Javascript. If you want to load all your data at once and keep it in memory as a large object with lots of properties (associative array), then you will find that most current desktops can only handle about 100k entries (with small key-value pairs) before performance really degrades.
If it is possible, you should see if there are ways to only load the data that is needed by the user for a given request / interaction. You can use AJAX to request needed data and prefetch data that you think the user may need.
So, my question is sort of based on experience, so I'm wondering about those out there who have tried to load datasets out there, what's a reasonable amount of data to load. My users have relatively big pipes, so I don't have to worry about modem users, but I do concern myself with processing times. I'm guessing my limit is somewhere in the 300-1024k range, but does anyone have a way or a website which has done something which can be a little more definitive?
I've run across this resource. It's from 2005, so I'd consider it out of date even though the general lesson seems to be pretty sound:
http://blogs.nitobi.com/dave/2005/09/29/javascript-benchmarking-iv-json-revisited/
I also came across this:
http://www.jamesward.com/census/
Is there is anything else out there worth checking into?
A typical JSON packet can (and should) be compressed using gzip by the web server to approx. 10% its initial size. So you're really looking at 30-100k. If those responses can be cached, then it's even less of a problem.
The size of the transmission should not be the deciding factor in whether a packet is "too much". Instead, look at how long it will take the browser to process this packet (update the UI, etc).
Actually parsing the JSON should be very fast, up to many megabytes of data. Turning that into something new in the UI will largely depend on how complicated the HTML you're producing is.