Create a new table named online:

time (int unix timestamp)
uid (int probably, user ID of user in question, relating to a user info table?)
sessid (char 32 I think)

When the user logs in, I assume you set the session.  Insert a row with the
current time (unix_timestamp(now()), User ID and the output of session_id()
in PHP.  This way you can run a query on that table at any time in one of
two ways.

 1. select count(id) from online where time>=(unix_timestamp(now())-900)

    This will give you the number of people who at least logged in in the
    last 15 minutes.  This isn't very accurate though... so

 2. If not already, put sessions in your SQL table.  This way you can run a
    query like (and John Holmes, please feel free to clean up my joins, i
    suck at them):

    select count(*) from online,sessions where
    online.sessid=sessions.sessid and>=(unix_timestamp(now())-900)

    This will give you the number of users who have done anything on the
    site in the last 15 minutes.  Change the 900 to 600 or 300 for 10 or 5
    minutes respectively.

Every week or so you'll want to "delete from online where time>=[some
number here, unix_timestamp(now()) minus how long you want to leave those
entries there]".

Depending on how often you want to do this and how busy your site is and
how focused on performance you are, I'd advise running it once per minute
and every time someone logs in, rather than once per page view, and put the
values generated into a text file and read it in with readfile().


On Fri, 3 Jan 2003, Bernain, Fernando G. wrote:

> I'm working in an app that requires to know who are "on line". When the user
> login the app, I use session in order to storage de name and login.  Its
> posible to do this???
> Thanks!
> Fernando Bernain
> Senior A
> Business Process Outsourcing
> KPMG Argentina
> Tel: 54 11 4316 5754
> Fax: 54 11 4316 5734
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Peter Beckman                                                  Internet Guy
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