@Override
  public boolean usesSharedMemory() {
    return true;
  }
IO engine that stores data in pmem devices such as DCPMM. This engine also mmaps the file from
the given path. But note that this path has to be a path on the pmem device so that when mmapped
the file's address is mapped to the Pmem's address space and not in the DRAM. Since this address
space is exclusive for the Pmem device there is no swapping out of the mmapped contents that
generally happens when DRAM's free space is not enough to hold the specified file's mmapped
contents. This gives us the option of using the {@code MemoryType#SHARED} type when serving the
data from this pmem address space. We need not copy the blocks to the onheap space as we need to
do for the case of {@code ExclusiveMemoryMmapIOEngine}.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/SharedMemoryMmapIOEngine.java