Library
Module
Module type
Parameter
Class
Class type
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 RO
The type for errors.
val disconnect : t -> unit Lwt.t
Disconnect from the key-value store. While this might take some time to complete, it can never result in an error.
type key = Key.t
The type for keys.
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.
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
.
get_partial t k ~offset ~length
is the length
bytes wide value bound at offset
of k
in t
.
If the size of k
is less than offset
, get_partial
returns an empty string. If the size of k
is less than offset
+length
, get_partial
returns a short string. The result is Error (`Value_expected k)
if k
refers to a dictionary in t
.
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
.
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.
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.
The type for write errors.
val pp_write_error : write_error Fmt.t
The pretty-printer for pp_write_error
.
val set : t -> key -> string -> (unit, write_error) Stdlib.result Lwt.t
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 set_partial :
t ->
key ->
offset:int ->
string ->
(unit, write_error) Stdlib.result Lwt.t
set_partial t k offset v
attempts to write v
at offset
in the value bound to k
in t
. If k
contains directories that do not exist, set_partial
will attempt to create them. If the size of k
is less than offset
, set_partial
appends v
at the end of k
. If the size of k
is greater than offset
+length of v
, set_partial
leaves the last bytes of k
unchanged.
The result is Error (`Value_expected k)
if k
refers to a dictionary in t
.
val remove : t -> key -> (unit, write_error) Stdlib.result Lwt.t
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 rename :
t ->
source:key ->
dest:key ->
(unit, write_error) Stdlib.result Lwt.t
rename t source dest
rename source
to dest
in t
. If source
and dest
are both bound to values in t
, dest
is removed and the binding of source
is moved to dest
. If dest
is bound to a dictionary in t
, source
is moved inside dest
. If source
is bound to a dictionary, the full dictionary is moved.
The result is Error (`Not_found source)
if source
does not exists in t
. The result is Error (`Value_expected source)
if source
is bound to a dictionary in t
and dest
is bound to a value in t
.
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
).