diff --git a/mars/services/lifecycle/supervisor/tracker.py b/mars/services/lifecycle/supervisor/tracker.py
index fc138003ac..c230575ebd 100644
--- a/mars/services/lifecycle/supervisor/tracker.py
+++ b/mars/services/lifecycle/supervisor/tracker.py
@@ -86,10 +86,6 @@ def _incref_chunks(self, chunk_keys: List[str], counts: List[int] = None):
             self._chunk_ref_counts[chunk_key] += count
 
     async def incref_chunks(self, chunk_keys: List[str], counts: List[int] = None):
-        logger.debug(
-            "Increase reference count for chunks %s",
-            {ck: self._chunk_ref_counts[ck] for ck in chunk_keys},
-        )
         self._check_ref_counts(chunk_keys, counts)
         return await asyncio.to_thread(self._incref_chunks, chunk_keys, counts=counts)
 
@@ -108,10 +104,6 @@ def _get_remove_chunk_keys(self, chunk_keys: List[str], counts: List[int] = None
 
     async def decref_chunks(self, chunk_keys: List[str], counts: List[int] = None):
         self._check_ref_counts(chunk_keys, counts)
-        logger.debug(
-            "Decrease reference count for chunks %s",
-            {ck: self._chunk_ref_counts[ck] for ck in chunk_keys},
-        )
         to_remove_chunk_keys = await asyncio.to_thread(
             self._get_remove_chunk_keys, chunk_keys, counts=counts
         )
diff --git a/mars/services/storage/api/oscar.py b/mars/services/storage/api/oscar.py
index c5a129ab58..8ca077e43a 100644
--- a/mars/services/storage/api/oscar.py
+++ b/mars/services/storage/api/oscar.py
@@ -189,7 +189,7 @@ async def fetch(
             self._session_id, [data_key], level, band_name, remote_address, error
         )
         if fetch_key:
-            return fetch_key
+            return fetch_key[0]
 
     @fetch.batch
     async def batch_fetch(self, args_list, kwargs_list):