diff --git a/hbs2-storage-simple/lib/HBS2/Storage/Compact.hs b/hbs2-storage-simple/lib/HBS2/Storage/Compact.hs
index 4dd9ef49..e5e4ddf9 100644
--- a/hbs2-storage-simple/lib/HBS2/Storage/Compact.hs
+++ b/hbs2-storage-simple/lib/HBS2/Storage/Compact.hs
@@ -1,6 +1,5 @@
-module HBS2.Storage.Compact
-  (
-  ) where
+{-# Language PatternSynonyms #-}
+module HBS2.Storage.Compact where
 
 
 import Data.Word
@@ -10,99 +9,271 @@ import Data.ByteString.Lazy qualified as LBS
 import Data.ByteString.Builder as B
 import Data.Binary.Get
 import Data.Coerce
+import Data.Function
+import Data.List qualified as List
+import Data.Maybe
+import Data.Map (Map)
+import Data.Map qualified as Map
+import Data.Foldable
+import Data.Traversable
 import Codec.Serialise
 import GHC.Generics
 -- import System.IO
 import Lens.Micro.Platform
 import Control.Monad.Except
+import Control.Monad.Trans.Maybe
+import Control.Monad
 import UnliftIO
 
+import Debug.Trace
+
 -- compact storage
 -- for the off-tree data representation
 -- may be it will be faster, than Simple storage
 -- who knows
 
 newtype EntryOffset = EntryOffset Word64
-                      deriving newtype (Ord,Eq,Num,Enum,Real)
+                      deriving newtype (Ord,Eq,Num,Enum,Real,Integral,Show)
                       deriving stock Generic
 
 newtype EntrySize = EntrySize Word64
-                    deriving newtype (Ord,Eq,Num,Enum,Real)
+                    deriving newtype (Ord,Eq,Num,Enum,Real,Integral,Show)
                     deriving stock Generic
 
+
+newtype EntryNum = EntryNum Word64
+                   deriving newtype (Ord,Eq,Num,Enum,Real,Integral,Show)
+                   deriving stock Generic
+
 data IndexEntry =
   IndexEntry
-  { idxEntryPrev   :: Maybe Word64
-  , idxEntryOffset :: EntryOffset
+  { idxEntryOffset :: EntryOffset
   , idxEntrySize   :: EntrySize
+  , idxEntrySeq    :: Word64
+  , idxEntryTomb   :: Bool
   , idxEntryKey    :: ByteString
   }
-  deriving stock Generic
+  deriving stock (Show,Generic)
 
 
+instance Serialise EntryOffset
+instance Serialise EntrySize
+instance Serialise EntryNum
+instance Serialise IndexEntry
+
 data Header =
   Header
-  { hdrMagic       :: Word16
-  , hdrVersion     :: Word16
-  , hdrIndexOffset :: EntryOffset
+  { hdrMagic        :: Word16
+  , hdrVersion      :: Word16
+  , hdrIndexOffset  :: EntryOffset
+  , hdrIndexEntries :: EntryNum
+  , hdrPrev         :: EntryOffset
   }
-  deriving stock Generic
+  deriving stock (Show,Generic)
 
 data CompactStorage =
   CompactStorage
-  { csHandle :: MVar Handle
+  { csHandle    :: MVar Handle
+  , csHeaderOff :: TVar EntryOffset
+  , csKeys      :: TVar (Map ByteString (Either IndexEntry ByteString))
   }
 
 type ForCompactStorage m = MonadIO m
 
-data CompactStorageOpenOpt = Default
-                             deriving stock (Eq,Ord)
+data CompactStorageOpenOpt
 
 data CompactStorageOpenError =
-       InvalidHeader
+         InvalidHeader
+       | BrokenIndex
   deriving stock (Typeable,Show)
 
 instance Exception CompactStorageOpenError
 
 
 compactStorageOpen :: ForCompactStorage m
-                   => CompactStorageOpenOpt
+                   => [CompactStorageOpenOpt]
                    -> FilePath
                    -> m CompactStorage
 
 compactStorageOpen _ fp = do
   ha <- openFile fp ReadWriteMode
+  sz <- hFileSize ha
   mha <- newMVar ha
-  header <- readHeader mha >>= maybe (throwIO InvalidHeader) pure
-  pure $ CompactStorage mha
+
+  hoff0 <- newTVarIO 0
+  keys0 <- newTVarIO mempty
+
+  if sz == 0 then
+    pure $ CompactStorage mha hoff0 keys0
+  else do
+    (p,header) <- readHeader mha Nothing >>= maybe (throwIO InvalidHeader) pure
+    traceM (show ("HEADER",header))
+    hoff <- newTVarIO p
+    let sto = CompactStorage mha hoff keys0
+    readIndex sto (hdrIndexOffset header) (hdrIndexEntries header)
+
+    flip fix (hdrPrev header) $ \next -> \case
+      0   -> pure ()
+      off ->  do
+        (_,pHeader) <- readHeader mha (Just off) >>= maybe (throwIO InvalidHeader) pure
+        traceM (show ("PHEADER",pHeader))
+        readIndex sto (hdrIndexOffset pHeader) (hdrIndexEntries pHeader)
+        next (hdrPrev pHeader)
+
+    pure sto
+
+readIndex :: ForCompactStorage m
+          => CompactStorage
+          -> EntryOffset
+          -> EntryNum
+          -> m ()
+readIndex sto offset num = liftIO do
+  withMVar (csHandle sto) $ \ha -> do
+    hSeek ha AbsoluteSeek (fromIntegral offset)
+    (rn,entries) <- flip fix (num, mempty, 0) $ \next left -> do
+        case left of
+          (0,acc,n)   -> pure (n,acc)
+          (n,acc,rn) -> do
+            what <- runMaybeT do
+
+                      slen <- liftIO (try @_ @IOException (LBS.hGet ha 2))
+                               <&> either (const Nothing) Just
+                               & MaybeT
+
+                      len <-  either (const Nothing) (Just . view _3) (runGetOrFail getWord16be slen)
+                                 & MaybeT . pure
+
+                      sIdx <- liftIO (try @_ @IOException (LBS.hGet ha (fromIntegral len)))
+                                >>= either (const mzero) pure
+
+                      deserialiseOrFail @IndexEntry sIdx
+                            & either (const mzero) pure
+
+            case what of
+              Nothing -> pure (0,mempty :: [IndexEntry])
+              Just idx -> next (pred n, idx : acc, succ rn)
+
+    when (rn /= num) do
+      throwIO BrokenIndex
+
+    atomically do
+      let new = Map.fromList [ (k,Left e) | e@(IndexEntry _ _ _ _ k) <- entries ]
+      -- readIndex from newer to older
+      -- so we keep only the newer values in map
+      modifyTVar (csKeys sto) (Map.unionWith (\_ b -> b) new)
 
 compactStorageCommit :: ForCompactStorage m => CompactStorage -> m ()
-compactStorageCommit sto = do
-  pure ()
+compactStorageCommit sto = liftIO do
+  withMVar (csHandle sto) $ \ha -> do
+    hSeek ha SeekFromEnd 0
+    kv <- readTVarIO (csKeys sto) <&> Map.toList
 
-appendHeader :: ForCompactStorage m => Handle -> EntryOffset -> m ()
-appendHeader ha offset = do
+    let items = [ (k, v) | (k, Right v) <- kv ]
+
+    unless (List.null items) do
+
+      off0 <- hTell ha
+
+      idxEntries <- flip fix (off0, items, mempty) $ \next (off, what, idx) -> do
+         case what of
+          [] -> pure idx
+          ((k,v):rest) -> do
+            BS.hPut ha v
+            let sz = fromIntegral $ BS.length v
+            next (off + sz, rest, IndexEntry (fromIntegral off) (fromIntegral sz) 0 False k : idx)
+
+      offIdx0 <- hTell ha <&> fromIntegral
+
+      for_ idxEntries $ \e -> do
+        let lbs = serialise e
+        LBS.hPut ha (B.toLazyByteString $
+                        word16BE (fromIntegral $ LBS.length lbs)
+                        <> B.lazyByteString lbs)
+
+      offPrev <- readTVarIO (csHeaderOff sto)
+
+      -- FIXME: maybe-slow-length-calc
+      appendHeader ha (Just offPrev) offIdx0 (fromIntegral $ length idxEntries)
+      hFlush ha
+
+      hSeek ha SeekFromEnd 0
+
+      offLast <- hTell ha <&> fromIntegral
+
+      atomically do
+        writeTVar (csHeaderOff sto) (offLast - headerSize 1)
+        for_ idxEntries $ \e -> do
+          modifyTVar (csKeys sto) (Map.insert (idxEntryKey e) (Left e))
+
+compactStoragePut :: ForCompactStorage m => CompactStorage -> ByteString -> ByteString -> m ()
+compactStoragePut sto k v = do
+  -- TODO: ASAP-do-not-write-value-if-not-changed
+  atomically $ modifyTVar (csKeys sto) (Map.insert k (Right v))
+
+compactStorageGet :: ForCompactStorage m => CompactStorage -> ByteString -> m (Maybe ByteString)
+compactStorageGet sto key = do
+  val <- readTVarIO (csKeys sto) <&> Map.lookup key
+  case val of
+    Nothing -> pure Nothing
+    Just (Right s) -> pure (Just s)
+    Just (Left e)  -> liftIO do
+      r <- withMVar (csHandle sto) $ \ha -> do
+             try @_ @IOException do
+                  hSeek ha AbsoluteSeek (fromIntegral $ idxEntryOffset e)
+                  BS.hGet ha (fromIntegral $ idxEntrySize e)
+      either throwIO (pure . Just) r
+
+compactStorageClose :: ForCompactStorage m => CompactStorage -> m ()
+compactStorageClose sto = do
+  compactStorageCommit sto
+  -- FIXME: hangs-forever-on-io-exception
+  w <- takeMVar (csHandle sto)
+  hClose w
+
+appendHeader :: ForCompactStorage m
+             => Handle
+             -> Maybe EntryOffset  -- prev. header
+             -> EntryOffset
+             -> EntryNum
+             -> m ()
+appendHeader ha hoffset offset num = do
   let bs =   word16BE headerMagic
           <> word16BE headerVersion
           <> word64BE (coerce offset)
-          <> byteString (BS.replicate 52 0)
+          <> word64BE (coerce num)
+          <> word64BE (coerce (fromMaybe 0 hoffset))
+          <> byteString (BS.replicate 4 0)
   liftIO $ LBS.hPut ha (B.toLazyByteString bs)
 
-readHeader :: ForCompactStorage m => MVar Handle -> m (Maybe Header)
-readHeader mha = do
-  bs <- liftIO $ withMVar mha $ \ha -> do
-    hSeek ha SeekFromEnd (-64)
-    LBS.hGet ha 64
+readHeader :: ForCompactStorage m
+           => MVar Handle
+           -> Maybe EntryOffset
+           -> m (Maybe (EntryOffset, Header))
+
+readHeader mha moff = do
+  (off,bs) <- liftIO $ withMVar mha $ \ha -> do
+
+    case moff of
+      Nothing -> do
+        hSeek ha SeekFromEnd (negate $ headerSize 1)
+      Just off -> do
+        hSeek ha AbsoluteSeek (fromIntegral off)
+
+    p <- hTell ha <&> fromIntegral
+    (p,) <$> LBS.hGet ha (headerSize 1)
 
   let what = flip runGetOrFail bs do
                 Header <$> getWord16be
                        <*> getWord16be
                        <*> getOffset
+                       <*> getNum
+                       <*> getOffset
 
-  pure $ either (const Nothing) (Just . view _3) what
+  pure $ either (const Nothing) (fmap (off,) . Just . view _3) what
 
   where
     getOffset = EntryOffset <$> getWord64be
+    getNum    = EntryNum    <$> getWord64be
 
 headerMagic :: Word16
 headerMagic = 32264
@@ -110,4 +281,8 @@ headerMagic = 32264
 headerVersion :: Word16
 headerVersion = 1
 
+headerSize :: Integral a => Word16 -> a
+headerSize 1 = fromIntegral (32 :: Integer)
+headerSize _ = error "unsupported header version"
+