I'm planning a chat-like web application, where whenever one user posts something, all other users (that is, people with their browser pointing to that site) would get instant updates. The common choice for this is comet-style messaging using long-polling AJAX requests. Writing the client-side part with jQuery isn't much of a problem.
But I wonder how to best implement the server-side part in PHP. The posts/messages will be stored in MySQL and the question is: After writing a new post to the database, how do I notify all waiting requests, that data is available for them without using polling? Polling would work, but it's ugly and wasting resources, thus, this is what I do not want:
while (timeout not reached) {
if ($database->has_changes())
break;
sleep(1);
}
handle_changes_if_any();
Is there some kind of MySQL feature that would help me here? Would some kind of IPC help? The server runs Apache.
You already mentioned one possible solution, which is to use AJAX polling to query a script periodically for updates. Polling would be done on the client side, and has nothing to do with the server side.
Another option would be to use a comet server such as Meteor. With this approach, your PHP script can notify the comet server of the new messages and the connected clients will receive the updates. Then it's just up to you to write the JavaScript to display the update to the user.
Related
I'm looking for the 'way to go' (i.e. the most efficient, most used, general accepted way) when it comes to the reloading of data from a web server to a front end. In the end application, I will have several output fields where data has to be written to, for example like this:
The data streams will be different from each other in the end application. The lines will have to be reloaded with fresh, up to date data from the server.
I have been thinking of using Ajax requests to update like every second, but there has to be an other way to do this. Ajax requests will cause a lot data traffic. Also, when using the Facebook chat, you don't have to wait every second, chats are received almost instantly. Yet I don't see any Ajax polling requests being made when I use the developer tools of Mozilla Firefox. This made me think if there would be a different way to do this.
I've looked into Node.js, but it appears that isn't possible with my host.
I have heard people talking about Ajax Push, is that what I should use? If so, can you give me a basic usage example?
If not, what would then be the way to go when having multiple data streams that have to be reloaded within a second?
Requirements are speed and low data traffic. It therefore wouldn't be an option to continuously poll the server, I think, because that would create an enormous overhead.
I don't think it's of any importance, but I'm using PHP5.3 in the back end and JavaScript with jQuery 1.9.1 in the front end.
This question has been asked a number of times, but in a slightly different ways. Here are a few references that are worth a read:
What are Long-Polling, Websockets, Server-Sent Events (SSE) and Comet?
Using comet with PHP?
Apache with Comet Support
Server Scalability - HTML 5 websockets vs Comet
How to implement event listening in PHP
In summary: if you are looking at building your solution using PHP on Apache then holding open persistent connections (HTTP long-polling or streaming) is going to use up resources very quickly (is highly inefficient). So, you would be better using a hosted solution (*disclaimer - I work for a hosted solution).
HTTP-Long polling and HTTP Streaming are solutions which have been superseded by Server-Sent Events and WebSockets. So, where possible (where the web client provides support) you should use one of these solutions before falling back to an HTTP-based solution. A good realtime web technology will automatically handle this for you.
Since your diagram shows you are subscribing to multiple data streams you should also consider a Publish/Subscribe solution that naturally fits with this. Again, a good realtime web tech solution will provide you with this.
Also see the realtime web technology guide.
I think what you are looking for is generally called Comet. The was this technique is often made to work is as follows:
The client (web browser) makes a request to the server for new data. This is not reloading the page, but rather is done in JavaScript
The server responds to the request when it has some data for the client. Again, this doesn't impact the UI since it isn't the page itself that's getting reloaded: the loaindg of data is done "in background" so to speak, in JavaScript code.
On the serve side, the request waits for new data, and returns the new data when available, or returns nothing if a timeout interval (defined on the server) is reached. This timeout is usually set to be lower than the browser HTTP timeout. The reason for this is so that the server can know whether a particular client got a particular piece of data. If the request is allowed to time out on the client side, the original request might be responded to by the server after the client has timed out, and the client will not get the data, even though the server thinks that it did.
The data is indeed usually transferred as JSON, but you can choose whatever encoding you'd like. See here for one example of how to do this. Goosh is another example of this technique, and so is Interactive Python Shell. The code for all is available.
On the PHP side you will want to create a page that will respond to these "background" JavaScript Comet requests. It could be the same page as the one that user loads, but let's say it is different, for ease of explanation. So the user loads index.php and the JavaScript Comet code calls getNewData.php to retrieve new data.
In your getNewData.php you will want to wait for your event and return the data then. You don't want to use polling for this, but there are PHP libraries that allow one to use various interprocess communication strategies to wait on events, see this question for instance. The high-level pseudocode for your getNewData.php would look as follows:
parse JSON request
Enter an efficient wait state (with timeout), waiting for your "new data is available" event
Did previous step time out?
Yes: send response indicating no data
No: send response with new data
I am writing a JavaScript for an in-browser IM client for the sake of practicing and learning JavaScript and AJAX.
I need to be able to check for a change in the file size of a text file that is being used as a temporary storage for 40-80 SQL entries that contain messages so that it can update the display.
At the moment I am using a setInterval function to periodically check for a change in file size using short PHP script, but this can cause issues, if the interval is to long, messages are delayed, if it is shorter, it means a lot of php scripts running very quickly, which takes up server resources.
What is the best way to do this if the main concern is to reduce server resource usage?
(I am running my server off of a rather low tech PC I've scraped together(2gb ram, 2.8ghz AMD seperon processor))
Preferably, I would want to do this using an AJAX event triggered by someone sending a message, I.E. When user B triggers the event that edits the file by pressing enter, that triggers a function on user A's side that updates the HTML file
Any ideas? I am open to any solution to this particular problem. I gave specific examples of what I want to happen in the specific languages in order to give a better idea of what it is I am attempting to do.
If there is a way to do this that isn't JavaScript/PHP, I'd also be open to exploring that as an option.
Doing this with PHP can be a bit cumbersome. You could try doing something like long polling where you keep the HTTP request open until the server has new data to send to the user. If messages are sent frequently, this might not be ideal. You might want to consider using event-driven web technologies like node.js with something like Socket.IO.
In any case, you'll likely want to maintain a connection with the server if you want to get the message in near real-time. There are ways to use WebSockets with PHP as well, but PHP isn't really the best for this because it's not designed to keep scripts running for long periods (also see What exactly entails setting up a PHP Websocket Server?).
Browsers & HTTP/ AJAX generally work by a "pull" model. The browser/ or AJAX sends the server a request, then the server answers a response.
There isn't generally much provision for the server to contact the browser, to "push" an event. This can however be simulated by a long-running request, to which the server writes data when the event/ or events occur.
For example, this could be a request that answers "empty" after a timeout of 10-30 seconds.. or the server returns & answers immediately, if there are event(s) in its queue.
With a Java server this is easy to do, and I've used this successfully for event notification in a major integration project a few years back.
However I'm not sure in PHP how much ability there is (probably very near zero) to maintain an overall server state, coordinate or communicate between threads/requests, or maintain event queues.
You could look into something like a Java webapp running on Tomcat. All you need is a basic web.xml and one Servlet class, and you can build just about anything from there.
I'm looking for the 'way to go' (i.e. the most efficient, most used, general accepted way) when it comes to the reloading of data from a web server to a front end. In the end application, I will have several output fields where data has to be written to, for example like this:
The data streams will be different from each other in the end application. The lines will have to be reloaded with fresh, up to date data from the server.
I have been thinking of using Ajax requests to update like every second, but there has to be an other way to do this. Ajax requests will cause a lot data traffic. Also, when using the Facebook chat, you don't have to wait every second, chats are received almost instantly. Yet I don't see any Ajax polling requests being made when I use the developer tools of Mozilla Firefox. This made me think if there would be a different way to do this.
I've looked into Node.js, but it appears that isn't possible with my host.
I have heard people talking about Ajax Push, is that what I should use? If so, can you give me a basic usage example?
If not, what would then be the way to go when having multiple data streams that have to be reloaded within a second?
Requirements are speed and low data traffic. It therefore wouldn't be an option to continuously poll the server, I think, because that would create an enormous overhead.
I don't think it's of any importance, but I'm using PHP5.3 in the back end and JavaScript with jQuery 1.9.1 in the front end.
This question has been asked a number of times, but in a slightly different ways. Here are a few references that are worth a read:
What are Long-Polling, Websockets, Server-Sent Events (SSE) and Comet?
Using comet with PHP?
Apache with Comet Support
Server Scalability - HTML 5 websockets vs Comet
How to implement event listening in PHP
In summary: if you are looking at building your solution using PHP on Apache then holding open persistent connections (HTTP long-polling or streaming) is going to use up resources very quickly (is highly inefficient). So, you would be better using a hosted solution (*disclaimer - I work for a hosted solution).
HTTP-Long polling and HTTP Streaming are solutions which have been superseded by Server-Sent Events and WebSockets. So, where possible (where the web client provides support) you should use one of these solutions before falling back to an HTTP-based solution. A good realtime web technology will automatically handle this for you.
Since your diagram shows you are subscribing to multiple data streams you should also consider a Publish/Subscribe solution that naturally fits with this. Again, a good realtime web tech solution will provide you with this.
Also see the realtime web technology guide.
I think what you are looking for is generally called Comet. The was this technique is often made to work is as follows:
The client (web browser) makes a request to the server for new data. This is not reloading the page, but rather is done in JavaScript
The server responds to the request when it has some data for the client. Again, this doesn't impact the UI since it isn't the page itself that's getting reloaded: the loaindg of data is done "in background" so to speak, in JavaScript code.
On the serve side, the request waits for new data, and returns the new data when available, or returns nothing if a timeout interval (defined on the server) is reached. This timeout is usually set to be lower than the browser HTTP timeout. The reason for this is so that the server can know whether a particular client got a particular piece of data. If the request is allowed to time out on the client side, the original request might be responded to by the server after the client has timed out, and the client will not get the data, even though the server thinks that it did.
The data is indeed usually transferred as JSON, but you can choose whatever encoding you'd like. See here for one example of how to do this. Goosh is another example of this technique, and so is Interactive Python Shell. The code for all is available.
On the PHP side you will want to create a page that will respond to these "background" JavaScript Comet requests. It could be the same page as the one that user loads, but let's say it is different, for ease of explanation. So the user loads index.php and the JavaScript Comet code calls getNewData.php to retrieve new data.
In your getNewData.php you will want to wait for your event and return the data then. You don't want to use polling for this, but there are PHP libraries that allow one to use various interprocess communication strategies to wait on events, see this question for instance. The high-level pseudocode for your getNewData.php would look as follows:
parse JSON request
Enter an efficient wait state (with timeout), waiting for your "new data is available" event
Did previous step time out?
Yes: send response indicating no data
No: send response with new data
I have a simple php page that displays data from a mysql database. I want it to update itself automatically when data gets changed on the server. (I don't want to update the page periodically at fix time intervals.) I guess I need the technology behind FB chat box or omegle. But I don't know how to implement it on php and mysql. I would be grateful if you could help me. Thanks.
You would need to look into WebSockets or a Comet server (which uses long-polling techniques) to accomplish a push system. Alternatively, instead of using push-like notification, you could make frequent polls to the server with nothing more than a request identifier and a timestamp, let the server decide if there is anything new since the last poll, and serve up the data if there is.
you can implement Comet technology which is opposite of Ajax. JavaScript Dojo Toolkit can be useful to handle this method well.
Dojo WebSocket
http://dojotoolkit.org/features/1.6/dojo-websocket
http://cometd.org/
"Comet is a web application model in which a long-held HTTP request allows a web server to push data to a browser, without the browser explicitly requesting it."
http://en.wikipedia.org/wiki/Comet_(programming))
I'm writing a website using PHP / MySQL. The website should allow users browsers to be automatically updated when a table is updated in a database (which is caused by someone inserting something though the PHP site). Basically, if the state of the table changes other users on the website should immediately see the changes.
I'm relatively new to PHP / AJAX and other web technologies. The only way I can think of doing this is to have the clients manually recheck the database every second or two via a timer (but this seems like a lot of wasted bandwidth). Is there some way to have the users automatically notified when the database changes?
Thank you!
You already had the solution in mind. You can use ajax to automatically check for changes.
It's not possible for the server to contact you when something has changed. It doesn't have to be bandwidth intensive when you lower the retrieval intervals. You can have Ajax check for a blank page with as little as possible text. That way the bandwidth usage wont be too bad.
Facebook does it this way too.
1) AJAX Polling.
As you say, use ajax to call the PHP on the server side to get
updates.
2) HTML5 Websockets.
Websockets are a new feature of HTML5 which allow the browser to keep a bi-directional TCP connection open to the server, where data can be transmitted both ways without polling. Currently this isn't as widely supported as ajax polling is.
3) Java Applet/ActiveX control.
Generally the most undesirable solution because of the user having to install third party software.