BigMemory permits caches to use an additional type of memory store outside the object heap, called the “off-heap store.” It’s available for both distributed and standalone use cases.
The off-heap store, which is not subject to Java garbage collection (GC), is 100 times faster than the DiskStore and allows extremely large caches to be created. Because off-heap data is stored in bytes, there are two implications:
- Only Serializable cache keys and values can be placed in the store, similar to DiskStore.
- Serialization and deserialization take place on putting and getting from the store. The theoretical difference in the overhead associated with serialization and deserialization disappears due to two effects:
- the MemoryStore holds the hottest subset of data from the off-heap store, already in deserialized form, and
- when the GC involved with larger heaps is taken into account, the off-heap store is faster on average.