We have decreased the memory allocated on the Appmon server, because it was oversized, from 128Gb to 96Gb. We can see than both memory and CPU level, work properly. But we have noticed a considerable increase in the "Sun/Oracle Code Cache used". What can it be the cause? what should we do?
You are saying about such high value on appmon server itself, yes? If there are no issues with not enough memory for server, it should be fine. The question is as well about sizing. After changing memory amount, did you check sizing settings as well? There is option to pick memory that server will allocate. You should pick option that contains your new value, or little bit lower. In general even for smaller sizing, appmon server may consume extra memory if available. But check if there isn't still 128GB left there.