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:

• DETS
• TokyoCabinet: TCERL
• QDBM
• Bitcask
• eLevelDB
• BerkleyDB
• ...

• Erlang R14B04+
• GCC 4.2+ or MS VisualStudio 2010+

$ 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:
  • DirName: database directory name
  • MapSize: database map size (see map.hrl)
  • EnvFlags: database environment flags (see map.hrl). The possible values are defined in emdb.hrl.
• close/2: closes the database
• put/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(). 

####Note: 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:

• Google's LevelDB
• SQLite
• Kyoto TreeDB
• BerkeleyDB

MDB performs better on 64-bit arch.

Should work on 32/64-bit architectures:

• Linux
• OSX
• FreeBSD
• Windows

• Unit tests
• PropEr testing
• Bulk "writing"

Volunteers are always welcome!

EMDB is Copyright (C) 2012 by Aleph Archives, and released under the OpenLDAP License.