log tree（merge）

http://www-users.cs.umn.edu/~he/diff/p256-severance.pdf

http://www.eecs.harvard.edu/~margo/cs165/papers/gp-lsm.pdf

http://www.cs.umb.edu/~poneil/lsmtree.pdf

https://people.eecs.berkeley.edu/~brewer/cs262/LFS.pdf

https://en.m.wikipedia.org/wiki/Log-structured_merge-tree

https://en.m.wikipedia.org/wiki/Log-structured_file_system