diff --git a/swh/storage/buffer.py b/swh/storage/buffer.py
--- a/swh/storage/buffer.py
+++ b/swh/storage/buffer.py
@@ -101,9 +101,9 @@
         )
 
     def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        summary: Dict[str, Dict] = self.storage.flush(object_types)
         if object_types is None:
             object_types = self.object_types
-        summary = {}  # type: Dict[str, Dict]
         for object_type in object_types:
             buffer_ = self._objects[object_type]
             batches = grouper(buffer_.values(), n=self.min_batch_size[object_type])
diff --git a/swh/storage/cassandra/storage.py b/swh/storage/cassandra/storage.py
--- a/swh/storage/cassandra/storage.py
+++ b/swh/storage/cassandra/storage.py
@@ -1002,3 +1002,6 @@
     def metadata_provider_get_by(self, provider):
         # TODO
         raise NotImplementedError("not yet supported for Cassandra")
+
+    def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        return {}
diff --git a/swh/storage/filter.py b/swh/storage/filter.py
--- a/swh/storage/filter.py
+++ b/swh/storage/filter.py
@@ -4,7 +4,7 @@
 # See top-level LICENSE file for more information
 
 
-from typing import Dict, Iterable, Set
+from typing import Dict, Iterable, Optional, Set
 
 from swh.model.model import (
     Content,
@@ -137,3 +137,6 @@
 
         fn = fn_by_object_type[object_type]
         return set(fn(missing_ids))
+
+    def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        return self.storage.flush(object_types)
diff --git a/swh/storage/in_memory.py b/swh/storage/in_memory.py
--- a/swh/storage/in_memory.py
+++ b/swh/storage/in_memory.py
@@ -1016,3 +1016,6 @@
 
     def diff_revision(self, revision, track_renaming=False):
         raise NotImplementedError("InMemoryStorage.diff_revision")
+
+    def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        return {}
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -1303,3 +1303,14 @@
             for more details).
         """
         ...
+
+    @remote_api_endpoint("flush")
+    def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        """For real backend storages (pg, storage, in-memory), this is expected to be a
+        noop operation doing nothing.
+
+        For proxy storages (especially buffer), this is expected to have a real
+        effect of forcing the actual writes to the backend.
+
+        """
+        ...
diff --git a/swh/storage/retry.py b/swh/storage/retry.py
--- a/swh/storage/retry.py
+++ b/swh/storage/retry.py
@@ -168,11 +168,8 @@
     def snapshot_add(self, snapshots: Iterable[Snapshot]) -> Dict:
         return self.storage.snapshot_add(snapshots)
 
-    @swh_retry
     def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
         """Specific case for buffer proxy storage failing to flush data
 
         """
-        if hasattr(self.storage, "flush"):
-            return self.storage.flush(object_types)
-        return {}
+        return self.storage.flush(object_types)
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -189,6 +189,7 @@
     @process_metrics
     def content_add(self, content: Iterable[Content]) -> Dict:
         ctime = now()
+
         contents = [attr.evolve(c, ctime=ctime) for c in content]
 
         objstorage_summary = self.objstorage.content_add(contents)
@@ -1215,3 +1216,6 @@
     @timed
     def diff_revision(self, revision, track_renaming=False):
         return diff.diff_revision(self, revision, track_renaming)
+
+    def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        return {}
diff --git a/swh/storage/tests/test_storage.py b/swh/storage/tests/test_storage.py
--- a/swh/storage/tests/test_storage.py
+++ b/swh/storage/tests/test_storage.py
@@ -3990,3 +3990,9 @@
             "absent",
             "Content too long",
         )
+
+    def test_flush(self, swh_storage):
+        """Calling clear buffers on real storage does nothing
+
+        """
+        assert swh_storage.flush() == {}
diff --git a/swh/storage/validate.py b/swh/storage/validate.py
--- a/swh/storage/validate.py
+++ b/swh/storage/validate.py
@@ -5,7 +5,7 @@
 
 import datetime
 import contextlib
-from typing import Dict, Iterable, List
+from typing import Dict, Iterable, Optional, List
 
 from swh.model.model import (
     BaseModel,
@@ -107,3 +107,6 @@
         with convert_validation_exceptions():
             origin = Origin.from_dict(origin)
         return self.storage.origin_add_one(origin)
+
+    def flush(self, object_types: Optional[Iterable[str]] = None) -> Dict:
+        return self.storage.flush(object_types)