EMDB is a NIF library for the Memory-Mapped Database database, aka. MDB.
The main purpose of this package is to provide a very fast Riak backend.
But this module could also be used as a general key-value store to replace:
$ make
The following functions were implemented:
open/1: equivalent to emdb:open(DirName, 10485760).open/2: equivalent to emdb:open(DirName, 10485760, 0).open/3: creates a new MDB database. This call also re-open an already existing one. Arguments are:
close/2: closes the databaseput/2: inserts Key with value Val into the database. Assumes that the key is not present, 'key_exit' is returned otherwise.get/1: retrieves the value stored with Key in the database.del/1: Removes the key-value with key Key from database.update/2: inserts Key with value Val into the database if the key is not present, otherwise updates Key to value Val.drop/1: deletes all key-value pairs in the database.$ make
$ ./start.sh
%% create a new database
1> {ok, Handle} = emdb:open("/tmp/emdb1").
%% insert the key <<"a">> with value <<"1">>
2> ok = Handle:put(<<"a">>, <<"1">>).
%% try to re-insert the same key <<"a">>
3> key_exist = Handle:put(<<"a">>, <<"2">>).
%% add a new key-value pair
4> ok = Handle:put(<<"b">>, <<"2">>).
%% search a non-existing key <<"c">>
5> none = Handle:get(<<"c">>).
%% retrieve the value for key <<"b">>
6> {ok, <<"2">>} = Handle:get(<<"b">>).
%% retrieve the value for key <<"a">>
7> {ok, <<"1">>} = Handle:get(<<"a">>).
%% delete key <<"b">>
8> ok = Handle:del(<<"b">>).
%% search a non-existing key <<"b">>
9> none = Handle:get(<<"b">>).
%% delete a non-existing key <<"z">>
10> none = Handle:del(<<"z">>).
%% ensure key <<"a">>'s value is still <<"1">>
11> {ok, <<"1">>} = Handle:get(<<"a">>).
%% update the value for key <<"a">>
12> ok = Handle:update(<<"a">>, <<"7">>).
%% check the new value for key <<"a">>
13> {ok, <<"7">>} = Handle:get(<<"a">>).
%% delete all key-value pairs in the database
14> ok = Handle:drop().
%% try to retrieve key <<"a">> value
15> none = Handle:get(<<"a">>).
%% close the database
16> ok = Handle:close().
...
17> q(). The code below creates a new database with 80GB MapSize, avoid fsync after each commit (for max speed) and use the experimental MDB_FIXEDMAP.
{ok, Handle} = emdb:open("/tmp/emdb2", 85899345920, ?MDB_NOSYNC bor ?MDB_FIXEDMAP).For maximum speed, this library use only binaries for both keys and values.
See the impressive microbench against:
MDB performs better on 64-bit arch.
Should work on 32/64-bit architectures:
Volunteers are always welcome!
EMDB is Copyright (C) 2012 by Aleph Archives, and released under the OpenLDAP License.