I have a searchbox which listens to keypress and calls the controller action to get results
These results shown for autocomplete as a dropdown. It works functionally.
Currently I have it set on each key press.
The problem is if I type 4/5 characters and debug the app, same line gets executed 4/5 times.
Is there a way to prevent this on the controller (I guess no)?
Is is good to send the request to the server on every character or do it based on time delay such as send the request after every 1 second delay while user keeps typing?
Thanks for reading.
add this to auto complete so it wait until minimum characters reach
minLength: (integer value what you preferred )
cheers
How can I abort a store load while the ajax call is still executing? I have a simple store with proxy type of 'ajax' and 'json' reader.
The documentation does not indicate any way to abort this. I have noticed that jsonp does allow aborting a load in progress. Do I have to switch to jsonp?
The motivation here is that I have a search bar and list object that gets populated with results. The actual search on the backend can take 5-10 seconds. So if a user starts a search then quickly wants to do another search (in case, for example, the first search was a typo), then the new search needs to abort the first search ajax call. Otherwise, I am seeing mixed results showing up in my search results.
As usual, any help is greatly appreciated!
Mohammad
The solution I have used in the past to solve this exact problem is to track each request with an incrementing counter and as requests complete I check the counter and if a request has been made with a higher counter I disregard the result.
I just read that some browsers would prevent HTTP polling (I guess by limiting the rate of requests)...
From https://github.com/sstrigler/JSJaC:
Note: As security restrictions of most modern browsers prevent HTTP
Polling from being usable anymore this module is disabled by default
now. If you want to compile it in use 'make polling'.
This could explain some misbehavior of some of my JavaScripts (sometimes requests are just not sent or retried, even if they were actually successful). But I couldn't find further information on details..
Questions
if it's "max. number of requests n per x seconds", what are the usual/default settings for x and n?
Is there any way good resource for this?
Any way to detect if a request has been "delayed" or "rejected" because of a rate limit?
Thanks for your help...
Stefan
Yes, as far as I am aware there is a default pool limit of 10 and a default request timeout of 30 seconds per request, however the timeout and poll limits can be controlled and different browsers implement different limitations!
Check out this Google implementation.
and this is an awesome implementation of catching a timeout error!
You can find the Firefox specifics HERE!
Internet Explorer specifics are controlled from inside the Windows registry.
Also have a look at this question.
Basically, the way you control is not by changing the browser limitations, but by abiding them. So you apply a technique called throttle-ing.
Think of it as creating a FIFO/priority queue of functions. A queue struct that takes xhr requests as members and enforces delay between them is an Xhr Poll. For instance, I am using
Jsonp to get data from a node.js server located on another domain and I am polling of course due to browser limitations. Otherwise, I get zero response back from the server and that is only because of browser limitations.
I am actually doing a console log for every request that's supposed to be sent, but not all of them are being logged. So the browser limits them.
I'll be even more specific with helping you out. I have a page on my website which is supposed to render a view for tens or even hundreds of articles. You go through them using a cool horizontal slider.
The current value of the slider matches the currrent 'page'. Since I am only displaying 5 articles per page and I can't exactly load thousands of articles 'onload' without severe performance implications, I load the articles for the current page. I get them from a MongoDB by sending a cross-domain request to a Python script.
The script is supposed to return an array of five objects with all the details I need to build the DOM elements for a 'page'. However, there are a couple of issues.
First, the slider works extremely fast, as it's more or less a value change. Even if there is drag drop functionality, key down events etc, the actual change takes miliseconds. However, the code of the slider looks something like this:
goog.events.listen(slider, goog.events.EventType.CHANGE, function() {
myProject.Articles.page(slider.getValue());
}
The slider.getValue() method returns an int with the current page number, so basically I have to load from:
currentPage * articlesPerPage to (currentPage * articlesPerPage + 1) - 1
But in order to load, i do something like this:
I have a storage engine(think of it as an array):
I check if the content is not already there
If it is, there is no point to make another request, so go forward with getting the DOM elements from the array with the already created DOM elements in place.
If it isn't, then I need to get it so I need to send that request I was mentioning, which would look something like(without accounting for browser limitations):
JSONP.send({'action':'getMeSomeArticles','start':start,'length': itemsPerPage, function(callback){
// now I just parse the callback quickly to make sure it is consistent
// create DOM elements, and populate the client side storage
// and update the view for the user.
}}
The problem comes from the speed with which you can change that slider. Since every change supposedly triggers a request(same would happen for normal Xhr requests), then you are basically crossing the limitations of all browsers, so without throttle-ing, there would be no 'callback' for most of the requests. 'callback' is the JS code returned by the JSONP request(which is more of a remote script inclusion than anything else).
So what I do is push a request to a priority queue, not POLL, as now I don't need to send multiple simultaneous requests. If the queue is empty, the recently added member is executed and everyone is happy. If it's not, then all non-completed requests in progress are cancelled and only the last one is executed.
Now in my particular case, I do a binary search(0(log n)) to see if the storage engine doesn't have data for the previous requests yet, which tells me if the previous request has been completed or not. If it has, then it's removed from the queue and the current one is processed, otherwise the new one fires. So an and so forth.
Again, for speed consideration and shit browser wanna-bes such as Internet Explorer, I do the above described procedure about 3-4 steps ahead. So I pre-load 20 pages ahead till everything is the client side storage engine. This way, every limitation is successfully dealt with.
The cooldown time is covered by the minimum time it would take to slide through 20 pages and the throttle-ing makes sure there are no more than 1 active requests at any given time(with backwards compatibility going as far as Internet Explorer 5).
The reason why I wrote all this is to give you an example trying to say that you cannot always enforce delay directly from the FIFO structure, as your calls may need to turn into what a user sees, and you don't exactly want to make a user wait 10-15 seconds for a single page to render.
Also, always minimize the polling and the need to poll(simultaneously fired Ajax events, as not all browsers actually do good things with them). For instance, instead of doing something like sending one request to get content and sending another for that content to be tracked as viewed in your app metrics, do as many tasks at server level as you possibly can!
Of course, you probably want to track your errors properly, so your Xhr object from your library of choice implement error handling for ajax and because you are an awesome developer you want to make use of them.
so say you have a try - catch block in place
The scenario is this:
An Ajax call has finished and it's supposed to return a JSON, but the call somehow failed. However, you try to parse the JSON and do whatever you need to do with it.
so
function onAjaxSuccess (ajaxResponse) {
try {
var yourObj = JSON.parse(ajaxRespose);
} catch (err) {
// Now I've actually seen this on a number of occasions, to log that an error occur
// a lot of developers will attempt to send yet another ajax request to log the
// failure of the previous one.
// for these reasons, workers exist.
myProject.worker.message('preferrably a pre-determined error code should go here');
// Then only the worker should again throttle and poll the ajax requests that log the
//specific error.
};
};
While I have seen various implementations that try to fire as many Xhr requests at the same time as they possible can until they encounter browser limitations, then do quite a good job at stalling the ones that haven't fired in wait for the browser 'cooldown', what I can advise you is to think about the following:
How important is speed for your app?
Just how scalable and how intensive the I/O will be?
If the answer to the first one is 'very' and to the latter 'OMFG modern technology', then try to optimize your code and architecture as much as you can so that you never need to send 10 simultaneous Xhr requests. Also, for large scale apps, multi-thread your processes. The JavaScript way to accomplish that is by using workers. Or you could call the ECMA board, tell them to make this a default, and then post it here so that the rest of us JS devs can enjoy native multi-threading in JS:)(how dafuq did they not think about this?!?!)
Stefan, quick answers below:
-if it's "max. number of requests n per x seconds", what are the usual/default settings for x and n?
This sounds more like a server restriction. The browser ones usually sound like:
-"the maximum requests for the same hostname is x"
-"the maximum connections for ANY hostname is y"
-Is there any way good resource for this?
http://www.browserscope.org/?category=network (also hover over table headers to see what is measured)
http://www.stevesouders.com/blog/2008/03/20/roundup-on-parallel-connections
-Any way to detect if a request has been "delayed" or "rejected" because of a rate limit?
You could look at the http headers for "Connection: close" to detect server restrictions but I am not aware of being able in JavaScript to read settings from so many browsers in a consistent, browser-independent way. (For Firefox, you could read this http://support.mozilla.org/en-US/questions/746848)
Hope this quick answer helps?
No, browser does not in any way affect polling. I think what was meant on that page is the same origin policy - you can only access the same host and port as your original page.
Only known limitation to connections themselves is that you usually can only have from two to four simultaneous connections to the same host.
I've written some apps with long poll, some with C++ backend with my own webserver, and one with PHP backend with Apache2.
My long poll timeout is 4..10 s. When something occurs, or 4..10 s passes, my server returns an empty response. Then the client immediatelly starts another AJAX request. I found that some browsers hangs up when I start AJAX call from previous AJAX handler, so I am using setTimeout() with a small value to start the next AJAX request.
When something happens on the client side, which should be sent to server, I use another AJAX request for it, but it's a one-way thing: the server does not send any response, and the client does not process anything. The result of the operation (if any) will be received on the long poll. It requires max. 2 connection to the server, which all browsers supports.
Keep in mind, that if there's 500 client, it means 500 server-side webserver thread, which will move together, occurring load peaks, because when something happens, the server have to report it at the same time for each clients, the clients will process it near same time long, they will start the next long request in the same time, and from then, the timeout will expire also at the same time, and furthcoming ones too. You can trick with rnd timeout, say 4 rnd(0..4), but it's worthless, if anything happens, they will "sync" again, all the request have to be served at the same time, when something reportable happens.
I've tested it thru a router, and it works. I assume, routers respects 4..10 lag, it's around the speed of a slow webapge (far, far away), which no router think, that it should be canceled.
My PHP work is a collaborative spreadsheet, it looks amazing when you hit enter and the stuff is updating simultaneously in several browsers. Have fun!
No limit for no of ajax requests. However it will be on same host & port.
Server can limit no of request from a machine based on its setting.
For example. A server can set so that if there are more than few request from same machine within specified time it will reject request.
After small mistake in javascript code, neverending loop was made witch each step calling 2 ajax requests. In firebug i could see more and more requests until firefox started to slow down, dont response and finally crash.
So, yes, there is a "limit" ;)
What is the best way deal with out-of-sequence Ajax requests (preferably using a jQuery)?
For example, an Ajax request is sent from the user's browser anytime a field changes. A user may change dog_name to "Fluffy", but a moment later, she changes it to "Spot". The first request is delayed for whatever reason, so it arrives at the server after the second, and her dog ends up being called "Fluffy" instead of "Spot".
I could pass along a client-side timestamp along with each request, and have the server track it as part of each Dog record and disregard earlier requests to change the same field (but only if there is a difference of less than 5 minutes, in case the user changes the time on her machine).
Is this approach sufficiently robust, or is there a better, more standardized approach?
EDIT:
Matt made a great point in his comment. It's much better to serialize requests to change the same field, so is there a standard way of implementing Ajax request queues?
EDIT #2
In response to #cherouvim's comment, I don't think I'd have to lock the form. The field changes to reflect the user's change, a change request is placed into the queue. If a request to change the same field is waiting in the queue, delete that old request. 2 things I still would have to address:
Placing a request into the queue is an asynchronous task. I could have the callback handler from the previous Ajax request send the next request in the queue. Javascript code isn't multi-threaded (or... is it?)
If a request fails, I would need the user interface to reflect the state of the last successful request. So, if the user changes the dog's name to "Spot" and the Ajax request fails, the field would have to be set back to "Fluffy" (the last value successfully committed).
What issues am I missing?
First of all you need to serialize server side processing for each client. If you are programming in Java then synchronizing execution on the http session object is sufficient. Serializing will help in case the second update comes while the first is being processed.
A second enhancement you can implement in your entity updating is http://en.wikipedia.org/wiki/Optimistic_concurrency_control. You add a version property (and column) for your entity. Each time an update happens this is incremented once. In fact the update statement looks like:
update ... set version=6 ... where id=? and version=5;
If affected rows from above pseudoquery query are 0 then someone else has managed to update the entity first. What you do then is up to you. Note that you need to be rendering the version on the html update form of the entity as a hidden parameter and sending it back to the server each time you update. On return you have to write back the updated version.
Generally the first enhancement would be enough. The second one will improve the system in case many people are editing the same entities at the same time. It solves the "lost update" problem.
I would implement a queue on the client side with chaining of successful requests or rollbacks on unsuccessful requests.
You need to define "unsuccessful", be it a timeout or a returned value.
I know the different options (None, ReadWrite, Read) and what they mean, but are there any other implications? Does ReadWrite take a performance hit compared to None, for example? Are there other consequences, or things to keep in mind?
I emailed Michael Schwarz, who wrote AjaxPro, and got the following reply:
Well, the main reason for adding this
attribute was to get rid of blocking
http requests. If you are accessing
session state variables in two
requests the 2nd one will need to wait
until the first one is finished. Since
I have added this attribute value I
always use
HttpSessionStateRequirement.None.
For more details see:
http://msdn.microsoft.com/en-us/library/system.web.sessionstate.irequiressessionstate.aspx
http://msdn.microsoft.com/en-us/library/system.web.sessionstate.ireadonlysessionstate%28VS.80%29.aspx
Browser waits for ajax call to complete even after abort has been called (jQuery)