> At points I've tried to keep three ORMs/DB libraries in my head at a time: AR, DataMapper, and Sequel ... At least AR has any story around things like optimis

> At points I've tried to keep three ORMs/DB libraries in my head at a time: AR, DataMapper, and Sequel ... At least AR has any story around things like optimistic and pessimistic locking That's rather dating your "at points". DataMapper hasn't seen an update since 2011, and Sequel's shipped with optimistic and pessimistic locking since early 2010.