Write to file and avoid having it overwritten for x amount of time

Question

I have an odd problem which I am trying to make solve now for a while. I have made a web app that gets data for a graph which is rendered using Highcharts.

The script fetches data from the DB, saves it into a file and renders the graph using $.getJson method in jquery which goes to another ajax file and processes the data that was saved. The user can spend x amount of time browsing the graph, and everytime the user changes the zoom level, an ajax request is sent back to my ajax page which again uses the saved data file to send graph data back.

The problem now is that if another user uses the app whilst the original user is still using the graph and its constantly being updated by the ajax file, the saved data file is overwritten and the original user will have the wrong graph data sent back to them.

I considered using $_SESSION however the data can be very large at times. Any other ideas?

Answer 1

If you've got multiple users, then don't use the same filename for all the users. e.g.

$cache_file = 'cache-' . session_id() . '.txt';

so that the file becomes tied to the particular user.

Answer 2

You could use different files for different users.

If you add the value of session_id() to your filename you'll have different files for every working session.