Tikv is very (very) slow (compared to redis, not sure about elogkv) and it's redis layer seems unmaintained. TiDB is very interesting product ; we tried to replace our massive mysql (master with multi read replica/standby's) system and it is just so slow that it's unusable really. Maybe it's great for other goals though, I don't know; I like the idea so we tried some setups with it.