How to understad "Aging rate" in Webacceleration

I have some doubt.

eg:2 webacceleration policies used by 2 virtual servers.

policies_1: max cache size : 50mb, aging rate:0 policies_2: max cache size : 50mb, aging rate:5

If policy_1'memory is full, which entry whill be freed???

If policy_1's entry will be free,there is no sense to use "Aging rate" because all the entries in policy_1 use the same priority(Aging rate).

If policy_2's entry will be free, it's useful to reduce memory of policy_2 accurately, but the memory of policy_1 is still full.