package mirage-kv-unix

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in-package search v0.2.0

mirage-kv-unix
- Mirage_kv_unix

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Loopback implementation of the FS signature.

type error = [

| Mirage_kv.error
| `Storage_error of Mirage_kv.Key.t * string

]

type write_error = [

| Mirage_kv.write_error
| `Storage_error of Mirage_kv.Key.t * string
| `Key_exists of Mirage_kv.Key.t

]

include Mirage_kv_lwt.RW
  with type error := error
   and type write_error := write_error

Read-write Stores

There is a trade-off between durability and performance. If you want performance, use the batch operation with a chain of sets and removes. They will be applied on the underlying storage layer all at once. Otherwise set and remove will cause a flush in the underlying storage layer every time, which could degrade performance.

include Mirage_kv.RO
  with type 'a io = 'a Lwt.t
  with type value = string
  with type error := error

Read-only key-value stores

val pp_error : error Fmt.t

pp_error is the pretty-printer for errors.

include Mirage_device.S with type 'a io = 'a Lwt.t

type 'a io = 'a Lwt.t

The type for potentially blocking I/O operation

type t

The type representing the internal state of the device

val disconnect : t -> unit io

Disconnect from the device. While this might take some time to complete, it can never result in an error.

type key = Mirage_kv.Key.t

The type for keys.

type value = string

The type for values.

val exists : t -> key -> ([ `Value | `Dictionary ] option, error) result io

exists t k is Some `Value if k is bound to a value in t, Some `Dictionary if k is a prefix of a valid key in t and None if no key with that prefix exists in t.

exists answers two questions: does the key exist and is it referring to a value or a dictionary.

An error occurs when the underlying storage layer fails.

val get : t -> key -> (value, error) result io

get t k is the value bound to k in t.

The result is Error (`Value_expected k) if k refers to a dictionary in t.

val list : 
  t ->
  key ->
  ((string * [ `Value | `Dictionary ]) list, error) result io

list t k is the list of entries and their types in the dictionary referenced by k in t.

The result is Error (`Dictionary_expected k) if k refers to a value in t.

val last_modified : t -> key -> (int * int64, error) result io

last_modified t k is the last time the value bound to k in t has been modified.

The modification time (d, ps) is a span for the signed POSIX picosecond span d * 86_400e12 + ps. d is a signed number of POSIX days and ps a number of picoseconds in the range [0;86_399_999_999_999_999L].

When the value bound to k is a dictionary, the modification time is the latest modification of all entries in that dictionary. This behaviour is only one level deep and not recursive.

val digest : t -> key -> (string, error) result io

digest t k is the unique digest of the value bound to k in t.

When the value bound to k is a dictionary, the digest is a unique and deterministic digest of its entries.

val pp_write_error : write_error Fmt.t

The pretty-printer for pp_write_error.

val set : t -> key -> value -> (unit, write_error) result io

set t k v replaces the binding k -> v in t.

Durability is guaranteed unless set is run inside an enclosing batch operation, where durability will be guaranteed at the end of the batch.

val remove : t -> key -> (unit, write_error) result io

remove t k removes any binding of k in t. If k was bound to a dictionary, the full dictionary will be removed.

Durability is guaranteed unless remove is run inside an enclosing batch operation, where durability will be guaranteed at the end of the batch.

val batch : t -> ?retries:int -> (t -> 'a io) -> 'a io

batch t f run f in batch. Ensure the durability of operations.

Since a batch is applied at once, the readings inside a batch will return the state before the entire batch. Concurrent operations will not affect other ones executed during the batch.

Batch applications can fail to apply if other operations are happening concurrently. In case of failure, f will run again with the most recent version of t. The result is Error `Too_many_retries if f is run for more then retries attemps (default is 13).

val connect : string -> t Lwt.t