[0] LSM (relies on ability to cache reads) vs. b-tree : https://tikv.org/deep-dive/key-value-engine/b-tree-vs-lsm/
[1] alternatives such as c-tree (lower memory usage/query time at cost of flexibility): https://en.wikipedia.org/wiki/C-trie
[2] radix variants : https://en.wikipedia.org/wiki/Radix_tree
[3] striped trie (distributed/parallel searching of shards) : https://www.agdresearch.com/striped-trie