Can you explain what is meant by second-level cache in the context of data storage systems?

The second level cache (Second Level Cache) in data storage systems, such as ORM frameworks like Hibernate, is a shared cache accessible to all sessions or transactions of the application. Unlike the first level cache, which exists only within a single session and is cleared after its completion, the second level cache stores data longer and allows reuse across different sessions.

This improves performance by reducing the number of database accesses, especially for frequently requested and rarely changed data. Typically, the second level cache is configured separately and can use external storage such as Ehcache, Infinispan, or Redis.

Example: if several users request the same data, the second level cache will allow loading it from memory rather than from the database, significantly speeding up the application.