A small problem about PROLOG.

My fourth point PROLOG now encountering problems.
I found this mailbox. I do not know that the mailbox can answer my
questions. If you know, please be sure to tell me. Thank you.
I was doing a PROLOG program in which part of the data is very
time-consuming calculations. So I think now it is cached.
But I'm looking for the corresponding function did not find the
appropriate function.

I need to term and cache data binding. When the term is not used. You
need to cache data recovered.

assert does not comply with my request, because I saved this forever.
recordz need a KEY, KEY and this can not be a term.

I tried to write C code. The results found that I did not know at what
time I should be to reclaim memory.

So I now how to do it?