Data freshness describes how up-to-date a copy of data (e.g. in a cache) is compared to the source version of the data (e.g. in the system-of-record (SoR). A stale copy is considered to be out of sync (or likely to be out of sync) with the SoR.

Databases (and other SORs) weren't built with caching outside of the database in mind, and therefore don't normally come with any default mechanism for notifying external processes when data has been updated or modified. Thus external components that have loaded data from the SoR have no direct way of ensuring that data is not stale.

Ehcache can assist you with reducing the likelihood that stale data is used by your application by expiring cache entries after some amount of configured time. Once expired, the entry is automatically removed from the cache.

For instance, the cache could be configured to expire entries five seconds after they are put into the cache - which is a time-to-live TTL setting. Or to expire entries 17 seconds after the last time the entry was retrieved from the cache - which is a time-to-idle TTI setting.

The expiration configuration that would be most appropriate for your cache (if any) would be a mixture of a business and technical decision based upon the requirements and assumptions of your application.