best approach for ocean ship tracking or similar

Say you have a web page that is supposed to continuously update the
positions of ships in the ocean or something similar. I am wondering
what is a good approach for this ? The page updates automatically
without the user hitting any buttons or clicking on anything.

What occurs to me is a timer that goes off in JavaScript every couple
of seconds and sends a request to the Rails server. The Rails server
may send back a Javascript call or a series of calls with some data in
order to update the position of the ships. Basically the ships
positions are maintained on the server which gets live feeds of where
the ships are.

I have done similar types of things such as periodically_update() in
rails. Sometimes these polling type things get carried away and tons
of them get sent to the server. It could be that say there are 10
clients and each of them sends a request every couple of seconds so
now you have basically that many more requests and so on. Also if the
server gets behind on requests, the client keeps on sending them. For
whatever reason, it seems like a pain in the neck these types of
polling actions. They seem to clutter up the log file really bad and
possibly slow everything down in some situations. but I am not sure if
there is any other way to do this ?

If not is there a more optimal way to approach the polling I wonder ?

You could use pushing from the server instead of polling. http://railscasts.com/episodes/260-messaging-with-faye

Best regards

Peter De Berdt

I'll add another railscast that appeared a few weeks later that might make implementing a push server even easier: http://railscasts.com/episodes/316-private-pub

Best regards

Peter De Berdt

> You could use pushing from the server instead of polling.http://railscasts.com/episodes/260-messaging-with-faye

I'll add another railscast that appeared a few weeks later that might
make implementing a push server even easier:http://railscasts.com/episodes/316-private-pub

Best regards

Peter De Berdt

Hi,

What is the basic concept here ? Is this standard HTML/Javascript ?
Everything in HTTP seems counter to that I have seen, so I am missing
something ?

Web technology has advanced quite a bit over the years. One feature of HTML5 is Websockets, which allow a persistent connection with the server and thus allowing the server to push data to the client without any client interaction or workarounds like polling with a certain interval.

Frameworks like Faye use Websockets when available and fall back to alternative methods for older browsers (a Flash-based socket or long polling, which is not the same as interval polling).

Simply put (it's actually a bit more complex) the following happens:
- User loads the page
- Javascript opens a persistent socket to the Faye server (using a named channel if you want it to)
- From your Rails app, you send messages to the Faye server, which automatically distributes it to all client connections for that particular channel.

The Railscasts explain the concept quite nicely IIRC.

Best regards

Peter De Berdt

Netscape introduced "server push" in 1995, FWIW :slight_smile:

(Worked fine. Unless you were using MSIE, which of course didn't
support it... )

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