diff --git a/Database/Monarch.hs b/Database/Monarch.hs
--- a/Database/Monarch.hs
+++ b/Database/Monarch.hs
@@ -3,9 +3,9 @@
 --
 module Database.Monarch
     (
-      module Database.Monarch.Types
+      module Database.Monarch.Raw
     , module Database.Monarch.Binary
     ) where
 
-import Database.Monarch.Types hiding (liftMonarch)
+import Database.Monarch.Raw hiding (liftMonarch)
 import Database.Monarch.Binary
diff --git a/Database/Monarch/Binary.hs b/Database/Monarch/Binary.hs
--- a/Database/Monarch/Binary.hs
+++ b/Database/Monarch/Binary.hs
@@ -23,7 +23,7 @@
 import Control.Applicative
 import Control.Monad.Error
 
-import Database.Monarch.Types
+import Database.Monarch.Raw
 import Database.Monarch.Utils
 
 -- | Store a record.
@@ -184,14 +184,14 @@
 
 -- | Get forward matching keys.
 forwardMatchingKeys :: ByteString -- ^ key prefix
-                    -> Int -- ^ maximum number of keys to be fetched
+                    -> Maybe Int -- ^ maximum number of keys to be fetched. 'Nothing' means unlimited.
                     -> Monarch [ByteString]
 forwardMatchingKeys prefix n = communicate request response
     where
       request = do
         putMagic 0x58
         putWord32be $ lengthBS32 prefix
-        putWord32be $ fromIntegral n
+        putWord32be $ fromIntegral (maybe (-1) id n)
         putByteString prefix
       response Success = do
         siz <- fromIntegral <$> parseWord32
diff --git a/Database/Monarch/MessagePack.hs b/Database/Monarch/MessagePack.hs
--- a/Database/Monarch/MessagePack.hs
+++ b/Database/Monarch/MessagePack.hs
@@ -12,7 +12,7 @@
 import Control.Applicative
 import Control.Monad.Error
 
-import Database.Monarch.Types
+import Database.Monarch.Raw
 import Database.Monarch.Utils
 
 -- | Store a record.
diff --git a/Database/Monarch/Raw.hs b/Database/Monarch/Raw.hs
new file mode 100644
--- /dev/null
+++ b/Database/Monarch/Raw.hs
@@ -0,0 +1,128 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE FlexibleContexts #-}
+-- | Raw definitions.
+module Database.Monarch.Raw
+    (
+      Monarch
+    , Connection, ConnectionPool
+    , withMonarchConn
+    , withMonarchPool
+    , runMonarchConn
+    , runMonarchPool
+    , ExtOption(..), RestoreOption(..), MiscOption(..)
+    , Code(..)
+    , liftMonarch
+    ) where
+
+import Data.IORef
+import Data.ByteString
+import Data.Conduit
+import Data.Conduit.Network
+import Data.Conduit.Pool
+import Control.Exception.Lifted (bracket)
+import Control.Monad.Error
+import Control.Applicative
+import Control.Monad.Trans.Control
+import Network.Socket
+
+-- | Connection with TokyoTyrant
+data Connection = Connection { connection :: Socket }
+
+-- | Connection pool with TokyoTyrant
+type ConnectionPool = Pool Connection
+
+-- | Error code
+data Code = Success
+          | InvalidOperation
+          | HostNotFound
+          | ConnectionRefused
+          | SendError
+          | ReceiveError
+          | ExistingRecord
+          | NoRecordFound
+          | MiscellaneousError
+            deriving (Eq, Show)
+
+instance Error Code
+
+-- | Options for scripting extension
+data ExtOption = RecordLocking -- ^ record locking
+               | GlobalLocking -- ^ global locking
+
+-- | Options for restore
+data RestoreOption = ConsistencyChecking -- ^ consistency checking
+
+-- | Options for miscellaneous operation
+data MiscOption = NoUpdateLog -- ^ omission of update log
+
+-- | A monad supporting TokyoTyrant access.
+newtype Monarch a =
+    Monarch { unMonarch :: ErrorT Code (Pipe ByteString ByteString ByteString () IO) a }
+    deriving ( Functor, Applicative, Monad, MonadIO
+             , MonadError Code )
+
+-- | Run Monarch with TokyoTyrant at target host and port.
+runMonarch :: MonadIO m =>
+              Connection
+           -> Monarch a
+           -> m (Either Code a)
+runMonarch conn action =
+    liftIO $ do
+      let c = connection conn
+      result <- newIORef (Left Success)
+      client action result (sourceSocket c) (sinkSocket c)
+      readIORef result
+
+client :: Monarch a
+       -> IORef (Either Code a)
+       -> Application IO
+client action result src sink = src $$ conduit =$ sink
+    where
+      conduit = runErrorT (unMonarch action) >>=
+                liftIO . writeIORef result
+
+-- | Create a TokyoTyrant connection and run the given action.
+-- Don't use the given 'Connection' outside the action.
+withMonarchConn :: (MonadBaseControl IO m, MonadIO m) =>
+                   String
+                -> Int
+                -> (Connection -> m a)
+                -> m a
+withMonarchConn host port f =
+    bracket open' close' f
+    where
+      open' = liftIO (Connection <$> getSocket host port)
+      close' = liftIO . sClose . connection
+
+-- | Create a TokyoTyrant connection pool and run the given action.
+-- Don't use the given 'ConnectionPool' outside the action.
+withMonarchPool :: (MonadBaseControl IO m, MonadIO m) =>
+                   String
+                -> Int
+                -> Int
+                -> (ConnectionPool -> m a)
+                -> m a
+withMonarchPool host port size f =
+    liftIO (createPool open' close' 1 20 size) >>= f
+    where
+      open' = Connection <$> getSocket host port
+      close' = sClose . connection
+
+-- | Run action with a connection.
+runMonarchConn :: (MonadBaseControl IO m, MonadIO m) =>
+                  Monarch a
+               -> Connection
+               -> m (Either Code a)
+runMonarchConn action conn = runMonarch conn action
+
+-- | Run action with a unused connection from the pool.
+runMonarchPool :: (MonadBaseControl IO m, MonadIO m) =>
+                  Monarch a
+               -> ConnectionPool
+               -> m (Either Code a)
+runMonarchPool action pool = withResource pool (\conn -> runMonarch conn action)
+
+-- | Lift
+liftMonarch :: Pipe ByteString ByteString ByteString () IO a
+            -> Monarch a
+liftMonarch = Monarch . lift
diff --git a/Database/Monarch/Types.hs b/Database/Monarch/Types.hs
deleted file mode 100644
--- a/Database/Monarch/Types.hs
+++ /dev/null
@@ -1,71 +0,0 @@
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
--- | Types.
-module Database.Monarch.Types
-    (
-      Monarch, runMonarch, liftMonarch
-    , ExtOption(..), RestoreOption(..), MiscOption(..)
-    , Code(..)
-    ) where
-
-import Data.IORef
-import Data.ByteString
-import Data.Conduit
-import Data.Conduit.Network
-import Control.Monad.Error
-import Control.Applicative
-
--- | Error code
-data Code = Success
-          | InvalidOperation
-          | HostNotFound
-          | ConnectionRefused
-          | SendError
-          | ReceiveError
-          | ExistingRecord
-          | NoRecordFound
-          | MiscellaneousError
-            deriving (Eq, Show)
-
-instance Error Code
-
--- | Options for scripting extension
-data ExtOption = RecordLocking -- ^ record locking
-               | GlobalLocking -- ^ global locking
-
--- | Options for restore
-data RestoreOption = ConsistencyChecking -- ^ consistency checking
-
--- | Options for miscellaneous operation
-data MiscOption = NoUpdateLog -- ^ omission of update log
-
--- | A monad supporting TokyoTyrant access.
-newtype Monarch a =
-    Monarch { unMonarch :: ErrorT Code (Pipe ByteString ByteString ByteString () IO) a }
-    deriving ( Functor, Applicative, Monad, MonadIO
-             , MonadError Code )
-
--- | Run Monarch with TokyoTyrant at target host and port.
-runMonarch :: MonadIO m =>
-              String
-           -> Int
-           -> Monarch a
-           -> m (Either Code a)
-runMonarch host port action =
-    liftIO $ do
-      result <- liftIO $ newIORef $ Left Success
-      let remote = ClientSettings port host
-      runTCPClient remote $ client action result
-      readIORef result
-
-client :: Monarch a
-       -> IORef (Either Code a)
-       -> Application IO
-client action result src sink = src $$ conduit =$ sink
-    where
-      conduit = runErrorT (unMonarch action) >>=
-                liftIO . writeIORef result
-
--- | Lift
-liftMonarch :: Pipe ByteString ByteString ByteString () IO a
-            -> Monarch a
-liftMonarch = Monarch . lift
diff --git a/Database/Monarch/Utils.hs b/Database/Monarch/Utils.hs
--- a/Database/Monarch/Utils.hs
+++ b/Database/Monarch/Utils.hs
@@ -23,7 +23,8 @@
 import Data.Binary.Get (runGet, getWord32be)
 import Control.Applicative
 import Control.Monad.Error
-import Database.Monarch.Types
+
+import Database.Monarch.Raw
 
 class BitFlag32 a where
     fromOption :: a -> Int32
diff --git a/monarch.cabal b/monarch.cabal
--- a/monarch.cabal
+++ b/monarch.cabal
@@ -1,5 +1,5 @@
 name:                monarch
-version:             0.3.0.0
+version:             0.4.0.0
 synopsis:            Monadic interface for TokyoTyrant.
 description:         This package provides simple monadic interface for TokyoTyrant.
 license:             BSD3
@@ -13,7 +13,7 @@
 
 library
   exposed-modules:     Database.Monarch
-                     , Database.Monarch.Types
+                     , Database.Monarch.Raw
                      , Database.Monarch.Binary
                      , Database.Monarch.MessagePack
   other-modules:       Database.Monarch.Utils
@@ -25,6 +25,11 @@
                      , network-conduit ==0.5.*
                      , binary ==0.5.*
                      , msgpack ==0.7.*
+                     , transformers ==0.3.*
+                     , network ==2.3.*
+                     , pool-conduit ==0.1.*
+                     , monad-control ==0.3.*
+                     , lifted-base ==0.1.*
 
 test-suite specs
   hs-source-dirs:      test, .
@@ -37,6 +42,10 @@
                      , network-conduit ==0.5.*
                      , binary ==0.5.*
                      , msgpack ==0.7.*
+                     , network ==2.3.*
+                     , pool-conduit ==0.1.*
+                     , monad-control ==0.3.*
+                     , lifted-base ==0.1.*
                      , hspec ==1.3.*
                      , HUnit ==1.2.*
 
diff --git a/test/test.hs b/test/test.hs
--- a/test/test.hs
+++ b/test/test.hs
@@ -53,13 +53,20 @@
            Monarch a
         -> Either Code a
         -> IO ()
-action `returns` expected = do
-  result <- runMonarch "localhost" 1978 $ do
-              vanish
-              result <- action
-              vanish
-              return result
-  result @?= expected
+action `returns` expected = connTest >> poolTest
+  where
+  connTest = do result <- withMonarchConn "localhost" 1978 $ runMonarchConn $ do
+                            vanish
+                            result <- action
+                            vanish
+                            return result
+                result @?= expected
+  poolTest = do result <- withMonarchPool "localhost" 1978 20 $ runMonarchPool $ do
+                            vanish
+                            result <- action
+                            vanish
+                            return result
+                result @?= expected
 
 casePutRecord :: Assertion
 casePutRecord =
@@ -247,7 +254,7 @@
         put "abra" "cadabra"
         put "abrac" "adabra"
         put "abraca" "dabra"
-        sort <$> forwardMatchingKeys "abra" 2
+        sort <$> forwardMatchingKeys "abra" (Just 2)
 
 casePutMsgPackRecord :: Assertion
 casePutMsgPackRecord =