For all regions, you have options to control memory use, back up your data to disk, and
keep stale data out of your cache.
Persistence and Overflow
You can persist data on disk for backup purposes and overflow it to disk to free up memory without completely removing the data from your cache.
Use eviction to control data region size.
Use expiration to keep data current by removing stale entries. You can also use it to remove entries you are not using so your region uses less space. Expired entries are reloaded the next time they are requested.