JPA talks about two kinds of caches (cache) :
* first-level cache (first-level cache) : caches data from a single transaction;
* second-level cache (second-level cache) : caches data for more than one transaction. The JPA provider can, but is not required to implement work with the second-level cache. This kind of cache can save access time and improve performance, but the downside is the ability to get outdated data.
