Ah Yes! Thank you very much again, for stopping me here!
This reminds me some yrs ago, I used threads shared hash for a simple chat server for our 20 something ppl dept, the hash queues unread messages... and what periodically happening was a Out of memory error, and the mesgs on the server and the server self gone. I finally have to backup the hash per every minute, and start another script to keep "ping" if the server alive or restart with restore data.
A simple hash could go in this way, I can imagine what is going to happen for such complex structure. Seems I can really ONLY rely on the db/fs now. It's not about accuracy or efficiency, but the basic stability and extendability.