Since the total size of the persistent storage may exceed the available size of the main memory in the system, mappings of regions in the storage files must be controlled dynamically. Mapping of a huge region whose size exceeds the available main memory causes swapping-outs of exceeded pages in the virtual memory system, and results in severe degradation of performance.
Therefore, only small fragments of the storage files can be mapped on the main memory. These fragments are frequently mapped and unmapped during operations. It must be noted here that unmapping of a region which contains an object under manipulation would surely lead to a system crash.
The conclusion is that a reference pointer has its own life cycle and the mapped region for the pointer must not be unmapped while the pointer is alive.