How many users are online to a particular website?

"Being online" can be implemented in several different ways from the website point of view. Most popular way is the one with sessions, in which client-side cookie contains session ID, and that cookie has a limited lifetime. On the server side, session object with same ID is maintained in memory, on disk or in database, typically automatically. Each session has own lifetime which is consistent with what was sent to the client browser as the cookie.

So each particular user is considered online all until cookie times out (looked from the client perspective) or until session object is removed from collection of live sessions (looked from the server perspective). This, however doesn't mean that this user is really online. He might have shut down the computer as well, and be considered online for couple of minutes or couple of hours more, falsely.

To conclude, counting online users typically boils down to a tradeoff of counting active sessions, hoping that it will not be too far away from the truth.

If you have administrative access to Web server (IIS, Apache...), then there are means to dig data out of it. For example, ASP.NET maintains performance counters giving own state, among other - giving number of active sessions. PHP maintains sessions on disk and some counting can be done on appropriate location (I'm not too familiar with this). And so on, there are general ways of getting this information when you're administrator.

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Zoran Horvat16y ago
"Being online" can be implemented in several different ways from the website point of view. Most popular way is the one with sessions, in which client-side cookie contains session ID, and that cookie has a limited lifetime. On the server side, session object with same ID is maintained in memory, on disk or in database, typically automatically. Each session has own lifetime which is consistent with what was sent to the client browser as the cookie.

So each particular user is considered online all until cookie times out (looked from the client perspective) or until session object is removed from collection of live sessions (looked from the server perspective). This, however doesn't mean that this user is really online. He might have shut down the computer as well, and be considered online for couple of minutes or couple of hours more, falsely.

To conclude, counting online users typically boils down to a tradeoff of counting active sessions, hoping that it will not be too far away from the truth.

If you have administrative access to Web server (IIS, Apache...), then there are means to dig data out of it. For example, ASP.NET maintains performance counters giving own state, among other - giving number of active sessions. PHP maintains sessions on disk and some counting can be done on appropriate location (I'm not too familiar with this). And so on, there are general ways of getting this information when you're administrator.
Satyapriya Nayak16y ago
Hi Zoran,

To any website it means,suppose in http://www.c-sharpcorner.com/ homepage it is seems to be Total Online Users:

thanks
Zoran Horvat16y ago
To which particular website? Is that a website for which you have a source code?