when to delete old files?

sneakyimp

i have a site that lets people upload images relating to a particular topic. topics expire. and when they have been expired 24 hours, i'd like to remove them and delete the associate images.

I am trying to decide what event to use on my site to trigger this deletion. I can think of a few possibilities:
1) CRON job - not sure how to set this up. have no experience setting up cron jobs and would like to be able to write code in PHP
2) check every time a user visits a page - might this cause performance issues if we are checking EVERY time a user visits?
3) set up a random lottery type event upon every page visit. set up random event so cleanup is averaging perhaps one time in 100.

I'm leaning toward #3. I have a file called top.php that gets included by all my files. I reckon I might put something like this in top:

$random_number = rand(1, 100);
if ($random_number == 50) {
  do_garbage_collection();
}

Can anyone see any down side to this? I figure if site traffic is low, cleanup might never happen--but on the other hand if site traffic is low cleanup won't really be necessary.

thoughts?

ColdFusion

I think cron is the best for this, you can set it to process the script at a time when visitor traffic is at its lowest during the day.

If you have a decent web panel with your host, setting up a cron job should be simple :rolleyes:

Weedpacket

#3 is how PHP's session-handling operates....

redrage

Go for cron if you have it available.

if you build it into the page it will slow it down since it has to do more processing.

sneakyimp

i was thinking about the tradeoffs between cron and my lottery style. I figure a 1 in 100 chance of getting a slow page is not too bad. I tested it for a situation where a few items were expired and it didn't even make a noticeable difference in performance.

Should the server come into heavy usage, things may be different. On the other hand, saving up tons of work to do and then doing it all at once might not be such a good idea either.