Ref.StoreData are divided into stores. Create one store for your project, where you will save all your data.
val open_store : string -> store Lwt.tOpen a store (and create it if it does not exist)
make_persistent store name default find a persistent value named name in store store from database, or create it with the default value default if it does not exist.
Same as make_persistent but the default value is evaluated only if needed
val make_persistent_lazy_lwt : 
  store:store ->
  name:string ->
  default:(unit -> 'a Lwt.t) ->
  'a t Lwt.tLwt version of make_persistent_lazy.
val get : 'a t -> 'a Lwt.tget pv gives the value of pv
val set : 'a t -> 'a -> unit Lwt.tset pv value sets a persistent value pv to value