Session variables vs DB hits

evenflow

Hi all,

Is there a limit to the number of variables that you can store in $_SESSION?

Does the number stored have any effect on performance or memory?

If I have a lot of information stored in a DB, that I need to be accessed between several pages. Would I be better doing a big DB hit and storing everything in the session, passing as URL parameters, or as hidden fields in a form?

Thanks!

NogDog

I don't think there's a logical limit, just a resource limit: memory for the $_SESSION array and disk space for the saved data between sessions.

It will probably be generally faster to access data from the session than from the DB, but not such a big difference that I'd worry a lot about it unless you are expecting to field a very high-traffic application (assuming your database and queries are reasonably normalized and optimized).

dagon

I would worry that the data could change and the session data be out of date, there could be some time between the first db select till the client goes to another page (and you don't know how long except for timing out the session) and uses that stored in session data. Depending on the application type that could be 'no issue' a 'minor issue' or a catastrophe.

NogDog

dagon;10893481 wrote:
I would worry that the data could change and the session data be out of date, there could be some time between the first db select till the client goes to another page (and you don't know how long except for timing out the session) and uses that stored in session data. Depending on the application type that could be 'no issue' a 'minor issue' or a catastrophe.

Good points to consider, and as such there's no simple, definitely always correct answer. It all depends on the specific requirements for what you are trying to accomplish.

Weedpacket

dagon's point is a good one. Caching may well speed things up, but it adds a layer of complexity when you need to keep cached copies of data fresh and synchronised with the originals.

You could of course have the best (or worst) of both worlds by storing your session data in the database ... 🙂