I know there were some issues on storing files of cache to retrieve them fast.

My solution was - creat subdirectiry structure like squid-cache uses.

But there was a problem - we do not know when cache old or not.
My solution was - checkpoint variable to differ old cache content from new content to know when just recache it.

Of course this structure can grow without limitations -but it's not a problem make cron script to just remove files from cache