When should I use session variables instead of cookies?

  • Sessions are stored on the server, which means clients do not have access to the information you store about them. Session data, being stored on your server, does not need to be transmitted in full with each page; clients just need to send an ID and the data is loaded from the server.

  • On the other hand, cookies are stored on the client. They can be made durable for a long time and would allow you to work more smoothly when you have a cluster of web servers. However, unlike sessions, data stored in cookies is transmitted in full with each page request.

  • Avoid storing data in cookies

    • It can be seen, read and manipulated by the end user, or intercepted by those with nefarious intent. You can’t trust any data in cookies, except for the “session_id”.
    • It increases your bandwidth, if you add 1k of data per page request per user, that might increase your bandwidth by 10-15%. This is perhaps not costly from a $$ perspective, but it could be from a performance perspective. It effectively would decrease your bandwidth on a per server by 10-15%, i.e., it might cause you to need more servers.
  • What you can store in session data depends on the amount of data and number of users you have. no_of_users * size_of_session_data must be less than the free memory available on your server.

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