This scheme is required to efficiently handle sparse files that might have extremely large file sizes with only a small fraction of valid data because only enough of the array is allocated to handle the currently mapped views of a file. For example, a 32-GB sparse file for which only 256 KB is mapped into the cache’s virtual address space would require a VACB array with three allocated index arrays because only one branch of the array has a mapping and a 32-GB (235 bytes) file requires a three- level array. If the cache manager didn’t use the multilevel VACB index array optimization for this file, it would have to allocate a VACB index array with 128,000 entries, or the equivalent of 1,000 VACB index arrays.