@@ -133,9 +133,11 @@ if err != nil {
 			if tracerr.Unwrap(err) != db.ErrNotFound {
 				return tracerr.Wrap(err)
 			} else if idx <= lastIdx {
-				return tracerr.Wrap(fmt.Errorf("account with idx %v not found: %w", idx, err))
+				return tracerr.Wrap(fmt.Errorf("account with idx %v (lastIdx: %v) "+
+					"not found: %w", idx, lastIdx, err))
 			} else {
-				return tracerr.Wrap(fmt.Errorf("unexpected stateDB error with idx %v: %w", idx, err))
+				return tracerr.Wrap(fmt.Errorf("unexpected stateDB error with idx %v "+
+					"(lastIdx: %v): %w", idx, lastIdx, err))
 			}
 		}
 		idxsNonce[i].Idx = idx

@@ -135,7 +135,7 @@ if err != nil {
 			return tracerr.Wrap(err)
 		}
 		kvdb.db = sto
-		kvdb.CurrentIdx = 255
+		kvdb.CurrentIdx = common.RollupConstReservedIDx // 255
 		kvdb.CurrentBatch = 0
 
 		return nil
@@ -204,7 +204,7 @@ if err != nil {
 			return tracerr.Wrap(err)
 		}
 		kvdb.db = sto
-		kvdb.CurrentIdx = 255
+		kvdb.CurrentIdx = common.RollupConstReservedIDx // 255
 		kvdb.CurrentBatch = 0
 
 		return nil
@@ -286,7 +286,7 @@ // used for an Account in the KVDB.
 func (kvdb *KVDB) GetCurrentIdx() (common.Idx, error) {
 	idxBytes, err := kvdb.db.Get(keyCurrentIdx)
 	if tracerr.Unwrap(err) == db.ErrNotFound {
-		return 0, nil
+		return common.RollupConstReservedIDx, nil // 255, nil
 	}
 	if err != nil {
 		return 0, tracerr.Wrap(err)
@@ -442,3 +442,8 @@ }
 
 	return nil
 }
+
+// Close the DB
+func (kvdb *KVDB) Close() {
+	kvdb.db.Close()
+}

@@ -195,3 +195,42 @@ require.NoError(t, err)
 		assert.LessOrEqual(t, len(checkpoints), keep)
 	}
 }
+
+func TestGetCurrentIdx(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.NoError(t, err)
+	defer require.NoError(t, os.RemoveAll(dir))
+
+	keep := 16
+	db, err := NewKVDB(dir, keep)
+	require.NoError(t, err)
+
+	idx, err := db.GetCurrentIdx()
+	require.NoError(t, err)
+	assert.Equal(t, common.Idx(255), idx)
+
+	db.Close()
+
+	db, err = NewKVDB(dir, keep)
+	require.NoError(t, err)
+
+	idx, err = db.GetCurrentIdx()
+	require.NoError(t, err)
+	assert.Equal(t, common.Idx(255), idx)
+
+	err = db.MakeCheckpoint()
+	require.NoError(t, err)
+
+	idx, err = db.GetCurrentIdx()
+	require.NoError(t, err)
+	assert.Equal(t, common.Idx(255), idx)
+
+	db.Close()
+
+	db, err = NewKVDB(dir, keep)
+	require.NoError(t, err)
+
+	idx, err = db.GetCurrentIdx()
+	require.NoError(t, err)
+	assert.Equal(t, common.Idx(255), idx)
+}

@@ -341,6 +341,11 @@ func (s *StateDB) MTGetRoot() *big.Int {
 	return s.MT.Root().BigInt()
 }
 
+// Close the StateDB
+func (s *StateDB) Close() {
+	s.db.Close()
+}
+
 // LocalStateDB represents the local StateDB which allows to make copies from
 // the synchronizer StateDB, and is used by the tx-selector and the
 // batch-builder. LocalStateDB is an in-memory storage.

@@ -532,3 +532,38 @@ require.NoError(t, err)
 		assert.LessOrEqual(t, len(checkpoints), keep)
 	}
 }
+
+func TestCurrentIdx(t *testing.T) {
+	dir, err := ioutil.TempDir("", "tmpdb")
+	require.NoError(t, err)
+	defer require.NoError(t, os.RemoveAll(dir))
+
+	keep := 16
+	sdb, err := NewStateDB(dir, keep, TypeSynchronizer, 32)
+	require.NoError(t, err)
+
+	idx := sdb.CurrentIdx()
+	assert.Equal(t, common.Idx(255), idx)
+
+	sdb.Close()
+
+	sdb, err = NewStateDB(dir, keep, TypeSynchronizer, 32)
+	require.NoError(t, err)
+
+	idx = sdb.CurrentIdx()
+	assert.Equal(t, common.Idx(255), idx)
+
+	err = sdb.MakeCheckpoint()
+	require.NoError(t, err)
+
+	idx = sdb.CurrentIdx()
+	assert.Equal(t, common.Idx(255), idx)
+
+	sdb.Close()
+
+	sdb, err = NewStateDB(dir, keep, TypeSynchronizer, 32)
+	require.NoError(t, err)
+
+	idx = sdb.CurrentIdx()
+	assert.Equal(t, common.Idx(255), idx)
+}