It's important to understand LMDB is an edge case design that wants the fastest reads possible and is willing to significantly burden the write path in that interest. Immutability is still a powerful approach. For a good example read the MSR papers on the hekaton main memory engine's approach: http://research.microsoft.com/apps/pubs/default.aspx?id=1787...

The original post isn't exactly wrong, it's just something of a straw man. We live in an era of terabyte disks. Cold data storage is cheap.