import Database.LMDB.Raw (MDB_dbi', MDB_env, mdb_dbi_open',
                          mdb_env_create, mdb_env_open,
                          mdb_env_set_mapsize, mdb_txn_begin,
                          mdb_txn_commit)

main :: IO ()
main = do
    -- Create an environment.
    env <- mdb_env_create

    -- The map size needs to be set. If you think 1 TiB will
    -- be more than enough, you can specify it like this.
    mdb_env_set_mapsize env (1024 * 1024 * 1024 * 1024)

    -- Open the environment. We are here assuming an existing directory
    -- that is either empty or already contains an LMDB database.
    mdb_env_open env "/somewhere/great-lmdb-dir" []

    -- Obtain the database handle.
    txn <- mdb_txn_begin env Nothing True
    dbi <- mdb_dbi_open' txn Nothing []
    mdb_txn_commit txn

import Control.Monad.Trans.Resource (MonadResource)
import Data.ByteString (ByteString)
import Database.LMDB.Raw (MDB_dbi', MDB_env)
import Streaming.Prelude (Of, Stream)

readLMDB :: (MonadResource m)
         => MDB_env
         -> MDB_dbi'
         -> Stream (Of (ByteString, ByteString)) m ()

writeLMDB :: (MonadResource m)
          => MDB_env
          -> MDB_dbi'
          -> Bool     -- If True, an exception will be thrown when attempting to re-insert a key.
          -> Stream (Of (ByteString, ByteString)) m r
          -> m r