How can I buffer logging across requests - Perl, log4Perl

I am looking for a way to only catch specific issues that occur after a certain threshold, over a given time frame.

e.g.

1. My web applications uses a set of keys send over POST
2. I am whitelisting the keys so I am only looking for specific keys within POST to be used by the application
3. But, I want to keep track of any keys that are unusual and not part of my list
4. But, I don't want to track each and every occurrence of a non-listed key - in case this is just a bot trying to get through
5. But, once a specific non-listed key hits a threshold - say 100 times in a week - I want to log it.

How can I accomplish this using Perl, ideally with something like log4Perl?

Thank you!

I think the answer would be 'use a hash'.

Define a hash in your app. Every time a bad request came in, extract the unique key, increment the hash value for that key. Once the value hits a threshold, spit out a warning. (And then reset it).

If you need cross-session persistence, you could probably use something like Storable to load and save the 'invalid requests' table.