* cratedb
  * actordb
  * tikv
  * tidb
  * rqlite

  * https://githubreviews.com/explore/databases/distributed-databases
  * https://db-engines.com/en/ranking

  * Location: id, user, point, time
  * User: id, username, email
  * Fence: id, polygon

== Queries

| insert Location at time T | 
| read Locations in timespan and is user |  
| insert Fence | 
| read Fences containing point and is user | 
| insert User | 
| read User is username |