tezos-stdlib-unix 17.3 · OCaml Package

Key-value store

This module defines a simple key-value store. The design is minimal and aims to be:

easy to use

safe when used in a concurrent setting

This key-value store also features a best effort mechanism relying on a cache to avoid I/Os.

This key-store use one file per key. Consequently, to control the number of file descriptors opened, a pool can be used.

type ('key, 'value) t

An abstract representation of a key-value store.

val init : 
  ?pool:unit Lwt_pool.t ->
  lru_size:int ->
  ('key -> 'value Stored_data.file) ->
  ('key, 'value) t

init ?pool ~lru_size file_of initialises a key-value store. This is a simple design where each value is stored into a single file.

For each key, we use file_of key to get the representation of a value as a file.

lru_size is a parameter that represents the number of different values that can be in memory. It is up to the user of this library to decide this number depending on the sizes of the values.

pool is an optional parameter that allows to control the maximum number of file descriptors opened at the same time.

val write_value : 
  ?override:bool ->
  ('key, 'value) t ->
  'key ->
  'value ->
  unit Tezos_error_monad.Error_monad.tzresult Lwt.t

write_value ?(override=false) t key value writes a value in the key value store. If a previous writing or read failed, the function will try again to write the value. If override is true, the value will be written even though there is already a written value for this key.

val write_values : 
  ?override:bool ->
  ('key, 'value) t ->
  ('key * 'value) Tezos_error_monad.TzLwtreslib.Seq.t ->
  unit Tezos_error_monad.Error_monad.tzresult Lwt.t

write_values ?(override=false) t seq writes a sequence of keys values onto the store (see write_value). If an error occurs, the first error is returned. This function guarantees that up to the data for which the error occured, the values where stored onto the disk.

val read_value : 
  ('key, 'value) t ->
  'key ->
  'value Tezos_error_monad.Error_monad.tzresult Lwt.t

read_value t key reads the value associated to key in the store. Fails if no value where attached to this key. The value read is the last one that was produced by a successful write.

val read_values : 
  ('key, 'value) t ->
  'key Tezos_error_monad.TzLwtreslib.Seq.t ->
  ('key * 'value Tezos_error_monad.Error_monad.tzresult)
    Tezos_error_monad.TzLwtreslib.Seq_s.t

read_values t keys produces a sequence of values associaed to the sequence of keys. This function is almost instantaneous since no reads are performed. Reads are done when the caller consumes the values of the sequence returned.

package tezos-stdlib-unix

Key-value store