Parameter History.C

Commit Store

include Indexable.S
include Indexable_intf.S_without_key_impl

Read-only stores

Read-only stores are store where it is only possible to read existing values.

type -'a t

The type for stores. The 'a phantom type carries information about the store mutability.

type key

The type for keys.

type value

The type for raw values.

val mem : [> Import.read ] t -> key -> bool

mem t k is true iff k is present in t.

val find : [> Import.read ] t -> key -> value option

find t k is Some v if k is associated to v in t and None is k is not present in t.

val close : 'a t -> unit

close t frees up all the resources associated with t. Any operations run on a closed handle will raise Closed.

type hash

The type of hashes of value.

val add : [> Import.write ] t -> value -> key

Write the contents of a value to the store, and obtain its key.

val unsafe_add : [> Import.write ] t -> hash -> value -> key

Same as add but allows specifying the value's hash directly. The backend might choose to discard that hash and/or can be corrupt if the hash is not consistent.

val index : [> Import.read ] t -> hash -> key option

Indexing maps the hash of a value to a corresponding key of that value in the store. For stores that are addressed by hashes directly, this is typically fun _t h -> Lwt.return (Key.of_hash h); for stores with more complex addressing schemes, index may attempt a lookup operation in the store.

In general, indexing is best-effort and reveals no information about the membership of the value in the store. In particular:

  • index t hash = Some key doesn't guarantee mem t key: the value with hash hash may still be absent from the store;
  • index t hash = None doesn't guarantee that there is no key such that mem t key and Key.to_hash key = hash: the value may still be present in the store under a key that is not indexed.
val batch : Import.read t -> ([ Import.read | Import.write ] t -> 'a) -> 'a

batch t f applies the writes in f in a separate batch. The exact guarantees depend on the implementation.

module Key : Key.S with type t = key and type hash = hash
module Info : Info.S

Commit info.

module Val : Commit_intf.S_generic_key with type t = value and type commit_key = key and module Info := Info

Val provides functions for commit values.

module Hash : Hash.Typed with type t = hash and type value = value
module Node : Node.Store with type key = Val.node_key

Node is the underlying node store.

val merge : [> Import.read_write ] t -> info:Info.f -> key option Merge.t

merge is the 3-way merge function for commit keys.