diff --git a/debian/control b/debian/control
--- a/debian/control
+++ b/debian/control
@@ -30,6 +30,9 @@
          python3-swh.objstorage (>= 0.0.17~),
          ${misc:Depends},
          ${python3:Depends}
+Breaks: python3-swh.archiver (<< 0.0.3~),
+        python3-swh.indexer (<< 0.0.48~),
+        python3-swh.vault (<< 0.0.19~)
 Description: Software Heritage storage utilities
 
 Package: python3-swh.storage.listener
diff --git a/swh/storage/common.py b/swh/storage/common.py
--- a/swh/storage/common.py
+++ b/swh/storage/common.py
@@ -16,8 +16,9 @@
         if 'cur' in kwargs and kwargs['cur']:
             return meth(self, *args, **kwargs)
         else:
-            with self.db.transaction() as cur:
-                return meth(self, *args, cur=cur, **kwargs)
+            db = self.get_db()
+            with db.transaction() as cur:
+                return meth(self, *args, db=db, cur=cur, **kwargs)
     return _meth
 
 
@@ -33,6 +34,7 @@
         if 'cur' in kwargs and kwargs['cur']:
             yield from meth(self, *args, **kwargs)
         else:
-            with self.db.transaction() as cur:
-                yield from meth(self, *args, cur=cur, **kwargs)
+            db = self.get_db()
+            with db.transaction() as cur:
+                yield from meth(self, *args, db=db, cur=cur, **kwargs)
     return _meth
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -42,14 +42,17 @@
         """
         try:
             if isinstance(db, psycopg2.extensions.connection):
-                self.db = Db(db)
+                self._db = Db(db)
             else:
-                self.db = Db.connect(db)
+                self._db = Db.connect(db)
         except psycopg2.OperationalError as e:
             raise StorageDBError(e)
 
         self.objstorage = get_objstorage(**objstorage)
 
+    def get_db(self):
+        return self._db
+
     def check_config(self, *, check_write):
         """Check that the storage is configured and ready to go."""
 
@@ -57,7 +60,7 @@
             return False
 
         # Check permissions on one of the tables
-        with self.db.transaction() as cur:
+        with self.get_db().transaction() as cur:
             if check_write:
                 check = 'INSERT'
             else:
@@ -94,7 +97,7 @@
                   content in
 
         """
-        db = self.db
+        db = self.get_db()
 
         def _unique_key(hash, keys=CONTENT_HASH_KEYS):
             """Given a hash (tuple or dict), return a unique key from the
@@ -152,7 +155,7 @@
                 db.skipped_content_add_from_temp(cur)
 
     @db_transaction
-    def content_update(self, content, keys=[], cur=None):
+    def content_update(self, content, keys=[], db=None, cur=None):
         """Update content blobs to the storage. Does nothing for unknown
         contents or skipped ones.
 
@@ -172,8 +175,6 @@
                 new hash column
 
         """
-        db = self.db
-
         # TODO: Add a check on input keys. How to properly implement
         # this? We don't know yet the new columns.
 
@@ -215,7 +216,7 @@
             yield {'sha1': obj_id, 'data': data}
 
     @db_transaction_generator
-    def content_get_metadata(self, content, cur=None):
+    def content_get_metadata(self, content, db=None, cur=None):
         """Retrieve content metadata in bulk
 
         Args:
@@ -224,15 +225,13 @@
         Returns:
             an iterable with content metadata corresponding to the given ids
         """
-        db = self.db
-
         db.store_tmp_bytea(content, cur)
 
         for content_metadata in db.content_get_metadata_from_temp(cur):
             yield dict(zip(db.content_get_metadata_keys, content_metadata))
 
     @db_transaction_generator
-    def content_missing(self, content, key_hash='sha1', cur=None):
+    def content_missing(self, content, key_hash='sha1', db=None, cur=None):
         """List content missing from storage
 
         Args:
@@ -254,8 +253,6 @@
             TODO: an exception when we get a hash collision.
 
         """
-        db = self.db
-
         keys = CONTENT_HASH_KEYS
 
         if key_hash not in CONTENT_HASH_KEYS:
@@ -272,7 +269,7 @@
             yield obj[key_hash_idx]
 
     @db_transaction_generator
-    def content_missing_per_sha1(self, contents, cur=None):
+    def content_missing_per_sha1(self, contents, db=None, cur=None):
         """List content missing from storage based only on sha1.
 
         Args:
@@ -285,14 +282,12 @@
             TODO: an exception when we get a hash collision.
 
         """
-        db = self.db
-
         db.store_tmp_bytea(contents, cur)
         for obj in db.content_missing_per_sha1_from_temp(cur):
             yield obj[0]
 
     @db_transaction_generator
-    def skipped_content_missing(self, content, cur=None):
+    def skipped_content_missing(self, content, db=None, cur=None):
         """List skipped_content missing from storage
 
         Args:
@@ -305,8 +300,6 @@
         """
         keys = CONTENT_HASH_KEYS
 
-        db = self.db
-
         db.mktemp('skipped_content', cur)
         db.copy_to(content, 'tmp_skipped_content',
                    keys + ['length', 'reason'], cur)
@@ -314,7 +307,7 @@
         yield from db.skipped_content_missing_from_temp(cur)
 
     @db_transaction
-    def content_find(self, content, cur=None):
+    def content_find(self, content, db=None, cur=None):
         """Find a content hash in db.
 
         Args:
@@ -331,8 +324,6 @@
                 nor sha256.
 
         """
-        db = self.db
-
         if not set(content).intersection(ALGORITHMS):
             raise ValueError('content keys must contain at least one of: '
                              'sha1, sha1_git, sha256, blake2s256')
@@ -384,7 +375,7 @@
         if not dirs_missing:
             return
 
-        db = self.db
+        db = self.get_db()
         with db.transaction() as cur:
             # Copy directory ids
             dirs_missing_dict = ({'id': dir} for dir in dirs_missing)
@@ -412,7 +403,7 @@
             db.directory_add_from_temp(cur)
 
     @db_transaction_generator
-    def directory_missing(self, directories, cur):
+    def directory_missing(self, directories, db=None, cur=None):
         """List directories missing from storage
 
         Args:
@@ -422,8 +413,6 @@
             missing directory ids
 
         """
-        db = self.db
-
         # Create temporary table for metadata injection
         db.mktemp('directory', cur)
 
@@ -435,9 +424,7 @@
             yield obj[0]
 
     @db_transaction_generator
-    def directory_get(self,
-                      directories,
-                      cur=None):
+    def directory_get(self, directories, db=None, cur=None):
         """Get information on directories.
 
         Args:
@@ -447,7 +434,6 @@
             List of directories as dict with keys and associated values.
 
         """
-        db = self.db
         keys = ('id', 'dir_entries', 'file_entries', 'rev_entries')
 
         db.mktemp('directory', cur)
@@ -459,7 +445,7 @@
             yield dict(zip(keys, line))
 
     @db_transaction_generator
-    def directory_ls(self, directory, recursive=False, cur=None):
+    def directory_ls(self, directory, recursive=False, db=None, cur=None):
         """Get entries for one directory.
 
         Args:
@@ -470,8 +456,6 @@
             List of entries for such directory.
 
         """
-        db = self.db
-
         if recursive:
             res_gen = db.directory_walk(directory, cur=cur)
         else:
@@ -481,7 +465,7 @@
             yield dict(zip(db.directory_ls_cols, line))
 
     @db_transaction
-    def directory_entry_get_by_path(self, directory, paths, cur=None):
+    def directory_entry_get_by_path(self, directory, paths, db=None, cur=None):
         """Get the directory entry (either file or dir) from directory with path.
 
         Args:
@@ -493,8 +477,6 @@
             The corresponding directory entry if found, None otherwise.
 
         """
-        db = self.db
-
         res = db.directory_entry_get_by_path(directory, paths, cur)
         if res:
             return dict(zip(db.directory_ls_cols, res))
@@ -531,7 +513,7 @@
                 - parents (list of sha1_git): the parents of this revision
 
         """
-        db = self.db
+        db = self.get_db()
 
         revisions_missing = set(self.revision_missing(
             set(revision['id'] for revision in revisions)))
@@ -559,7 +541,7 @@
                        ['id', 'parent_id', 'parent_rank'], cur)
 
     @db_transaction_generator
-    def revision_missing(self, revisions, cur=None):
+    def revision_missing(self, revisions, db=None, cur=None):
         """List revisions missing from storage
 
         Args:
@@ -569,15 +551,13 @@
             missing revision ids
 
         """
-        db = self.db
-
         db.store_tmp_bytea(revisions, cur)
 
         for obj in db.revision_missing_from_temp(cur):
             yield obj[0]
 
     @db_transaction_generator
-    def revision_get(self, revisions, cur):
+    def revision_get(self, revisions, db=None, cur=None):
         """Get all revisions from storage
 
         Args:
@@ -588,12 +568,9 @@
                 revision doesn't exist)
 
         """
-
-        db = self.db
-
         db.store_tmp_bytea(revisions, cur)
 
-        for line in self.db.revision_get_from_temp(cur):
+        for line in db.revision_get_from_temp(cur):
             data = converters.db_to_revision(
                 dict(zip(db.revision_get_cols, line))
             )
@@ -603,7 +580,7 @@
             yield data
 
     @db_transaction_generator
-    def revision_log(self, revisions, limit=None, cur=None):
+    def revision_log(self, revisions, limit=None, db=None, cur=None):
         """Fetch revision entry from the given root revisions.
 
         Args:
@@ -614,8 +591,6 @@
             List of revision log from such revisions root.
 
         """
-        db = self.db
-
         for line in db.revision_log(revisions, limit, cur):
             data = converters.db_to_revision(
                 dict(zip(db.revision_get_cols, line))
@@ -626,7 +601,7 @@
             yield data
 
     @db_transaction_generator
-    def revision_shortlog(self, revisions, limit=None, cur=None):
+    def revision_shortlog(self, revisions, limit=None, db=None, cur=None):
         """Fetch the shortlog for the given revisions
 
         Args:
@@ -638,13 +613,11 @@
 
         """
 
-        db = self.db
-
         yield from db.revision_shortlog(revisions, limit, cur)
 
     @db_transaction_generator
     def revision_log_by(self, origin_id, branch_name=None, timestamp=None,
-                        limit=None, cur=None):
+                        limit=None, db=None, cur=None):
         """Fetch revision entry from the actual origin_id's latest revision.
 
         Args:
@@ -662,8 +635,6 @@
             None if no revision matching this combination is found.
 
         """
-        db = self.db
-
         # Retrieve the revision by criterion
         revisions = list(db.revision_get_by(
             origin_id, branch_name, timestamp, limit=1, cur=cur))
@@ -673,7 +644,7 @@
 
         revision_id = revisions[0][0]
         # otherwise, retrieve the revision log from that revision
-        yield from self.revision_log([revision_id], limit, cur=cur)
+        yield from self.revision_log([revision_id], limit, db=db, cur=cur)
 
     def release_add(self, releases):
         """Add releases to the storage
@@ -695,7 +666,7 @@
                 - author_email (bytes): the email of the release author
 
         """
-        db = self.db
+        db = self.get_db()
 
         release_ids = set(release['id'] for release in releases)
         releases_missing = set(self.release_missing(release_ids))
@@ -717,7 +688,7 @@
             db.release_add_from_temp(cur)
 
     @db_transaction_generator
-    def release_missing(self, releases, cur=None):
+    def release_missing(self, releases, db=None, cur=None):
         """List releases missing from storage
 
         Args:
@@ -727,8 +698,6 @@
             a list of missing release ids
 
         """
-        db = self.db
-
         # Create temporary table for metadata injection
         db.store_tmp_bytea(releases, cur)
 
@@ -736,7 +705,7 @@
             yield obj[0]
 
     @db_transaction_generator
-    def release_get(self, releases, cur=None):
+    def release_get(self, releases, db=None, cur=None):
         """Given a list of sha1, return the releases's information
 
         Args:
@@ -755,8 +724,6 @@
             ValueError: if the keys does not match (url and type) nor id.
 
         """
-        db = self.db
-
         # Create temporary table for metadata injection
         db.store_tmp_bytea(releases, cur)
 
@@ -767,7 +734,7 @@
 
     @db_transaction
     def snapshot_add(self, origin, visit, snapshot, back_compat=False,
-                     cur=None):
+                     db=None, cur=None):
         """Add a snapshot for the given origin/visit couple
 
         Args:
@@ -791,8 +758,6 @@
             back_compat (bool): whether to add the occurrences for
               backwards-compatibility
         """
-        db = self.db
-
         if not db.snapshot_exists(snapshot['id'], cur):
             db.mktemp_snapshot_branch(cur)
             db.copy_to(
@@ -834,10 +799,10 @@
                 'target_type': target_type,
             })
 
-        self.occurrence_add(occurrences, cur=cur)
+        self.occurrence_add(occurrences, db=db, cur=cur)
 
     @db_transaction
-    def snapshot_get(self, snapshot_id, cur=None):
+    def snapshot_get(self, snapshot_id, db=None, cur=None):
         """Get the snapshot with the given id
 
         Args:
@@ -848,8 +813,6 @@
              branches:: a list of branches contained by the snapshot
 
         """
-        db = self.db
-
         branches = {}
         for branch in db.snapshot_get_by_id(snapshot_id, cur):
             branch = dict(zip(db.snapshot_get_cols, branch))
@@ -869,7 +832,7 @@
         return None
 
     @db_transaction
-    def snapshot_get_by_origin_visit(self, origin, visit, cur=None):
+    def snapshot_get_by_origin_visit(self, origin, visit, db=None, cur=None):
         """Get the snapshot for the given origin visit
 
         Args:
@@ -881,16 +844,14 @@
              branches:: a dictionary containing the snapshot branch information
 
         """
-        db = self.db
-
         snapshot_id = db.snapshot_get_by_origin_visit(origin, visit, cur)
 
         if snapshot_id:
-            return self.snapshot_get(snapshot_id, cur=cur)
+            return self.snapshot_get(snapshot_id, db=db, cur=cur)
         else:
             # compatibility code during the snapshot migration
             origin_visit_info = self.origin_visit_get_by(origin, visit,
-                                                         cur=cur)
+                                                         db=db, cur=cur)
             if origin_visit_info is None:
                 return None
             ret = {'id': None}
@@ -900,7 +861,8 @@
         return None
 
     @db_transaction
-    def snapshot_get_latest(self, origin, allowed_statuses=None, cur=None):
+    def snapshot_get_latest(self, origin, allowed_statuses=None, db=None,
+                            cur=None):
         """Get the latest snapshot for the given origin, optionally only from visits
         that have one of the given allowed_statuses.
 
@@ -916,16 +878,14 @@
              id:: identifier for the snapshot
              branches:: a dictionary containing the snapshot branch information
         """
-        db = self.db
-
         origin_visit = db.origin_visit_get_latest_snapshot(
             origin, allowed_statuses=allowed_statuses, cur=cur)
         if origin_visit:
             origin_visit = dict(zip(db.origin_visit_get_cols, origin_visit))
-            return self.snapshot_get(origin_visit['snapshot'], cur=cur)
+            return self.snapshot_get(origin_visit['snapshot'], db=db, cur=cur)
 
     @db_transaction
-    def occurrence_add(self, occurrences, cur=None):
+    def occurrence_add(self, occurrences, db=None, cur=None):
         """Add occurrences to the storage
 
         Args:
@@ -943,8 +903,6 @@
                   occurrence
 
         """
-        db = self.db
-
         db.mktemp_occurrence_history(cur)
         db.copy_to(occurrences, 'tmp_occurrence_history',
                    ['origin', 'branch', 'target', 'target_type', 'visit'], cur)
@@ -952,7 +910,7 @@
         db.occurrence_history_add_from_temp(cur)
 
     @db_transaction_generator
-    def occurrence_get(self, origin_id, cur=None):
+    def occurrence_get(self, origin_id, db=None, cur=None):
         """Retrieve occurrence information per origin_id.
 
         Args:
@@ -962,7 +920,6 @@
             List of occurrences matching criterion.
 
         """
-        db = self.db
         for line in db.occurrence_get(origin_id, cur):
             yield {
                 'origin': line[0],
@@ -972,7 +929,7 @@
             }
 
     @db_transaction
-    def origin_visit_add(self, origin, ts, cur=None):
+    def origin_visit_add(self, origin, ts, db=None, cur=None):
         """Add an origin_visit for the origin at ts with status 'ongoing'.
 
         Args:
@@ -992,12 +949,12 @@
 
         return {
             'origin': origin,
-            'visit': self.db.origin_visit_add(origin, ts, cur)
+            'visit': db.origin_visit_add(origin, ts, cur)
         }
 
     @db_transaction
     def origin_visit_update(self, origin, visit_id, status, metadata=None,
-                            cur=None):
+                            db=None, cur=None):
         """Update an origin_visit's status.
 
         Args:
@@ -1010,11 +967,11 @@
             None
 
         """
-        return self.db.origin_visit_update(origin, visit_id, status, metadata,
-                                           cur)
+        return db.origin_visit_update(origin, visit_id, status, metadata, cur)
 
     @db_transaction_generator
-    def origin_visit_get(self, origin, last_visit=None, limit=None, cur=None):
+    def origin_visit_get(self, origin, last_visit=None, limit=None, db=None,
+                         cur=None):
         """Retrieve all the origin's visit's information.
 
         Args:
@@ -1028,14 +985,13 @@
             List of visits.
 
         """
-        db = self.db
         for line in db.origin_visit_get_all(
                 origin, last_visit=last_visit, limit=limit, cur=cur):
-            data = dict(zip(self.db.origin_visit_get_cols, line))
+            data = dict(zip(db.origin_visit_get_cols, line))
             yield data
 
     @db_transaction
-    def origin_visit_get_by(self, origin, visit, cur=None):
+    def origin_visit_get_by(self, origin, visit, db=None, cur=None):
         """Retrieve origin visit's information.
 
         Args:
@@ -1045,17 +1001,15 @@
             The information on that particular (origin, visit)
 
         """
-        db = self.db
-
         ori_visit = db.origin_visit_get(origin, visit, cur)
         if not ori_visit:
             return None
 
-        ori_visit = dict(zip(self.db.origin_visit_get_cols, ori_visit))
+        ori_visit = dict(zip(db.origin_visit_get_cols, ori_visit))
 
         if ori_visit['snapshot']:
-            ori_visit['occurrences'] = self.snapshot_get(ori_visit['snapshot'],
-                                                         cur=cur)['branches']
+            ori_visit['occurrences'] = self.snapshot_get(
+                ori_visit['snapshot'], db=db, cur=cur)['branches']
             return ori_visit
 
         # TODO: remove Backwards compatibility after snapshot migration
@@ -1077,6 +1031,7 @@
                         branch_name=None,
                         timestamp=None,
                         limit=None,
+                        db=None,
                         cur=None):
         """Given an origin_id, retrieve occurrences' list per given criterions.
 
@@ -1091,13 +1046,10 @@
             found.
 
         """
-        for line in self.db.revision_get_by(origin_id,
-                                            branch_name,
-                                            timestamp,
-                                            limit=limit,
-                                            cur=cur):
+        for line in db.revision_get_by(origin_id, branch_name, timestamp,
+                                       limit=limit, cur=cur):
             data = converters.db_to_revision(
-                dict(zip(self.db.revision_get_cols, line))
+                dict(zip(db.revision_get_cols, line))
             )
             if not data['type']:
                 yield None
@@ -1105,7 +1057,7 @@
             yield data
 
     @db_transaction_generator
-    def release_get_by(self, origin_id, limit=None, cur=None):
+    def release_get_by(self, origin_id, limit=None, db=None, cur=None):
         """Given an origin id, return all the tag objects pointing to heads of
         origin_id.
 
@@ -1118,15 +1070,14 @@
             found.
 
         """
-
-        for line in self.db.release_get_by(origin_id, limit=limit, cur=cur):
+        for line in db.release_get_by(origin_id, limit=limit, cur=cur):
             data = converters.db_to_release(
-                dict(zip(self.db.release_get_cols, line))
+                dict(zip(db.release_get_cols, line))
             )
             yield data
 
     @db_transaction
-    def object_find_by_sha1_git(self, ids, cur=None):
+    def object_find_by_sha1_git(self, ids, db=None, cur=None):
         """Return the objects found with the given ids.
 
         Args:
@@ -1142,8 +1093,6 @@
             - object_id: the numeric id of the object found.
 
         """
-        db = self.db
-
         ret = {id: [] for id in ids}
 
         for retval in db.object_find_by_sha1_git(ids, cur=cur):
@@ -1156,7 +1105,7 @@
     origin_keys = ['id', 'type', 'url', 'lister', 'project']
 
     @db_transaction
-    def origin_get(self, origin, cur=None):
+    def origin_get(self, origin, db=None, cur=None):
         """Return the origin either identified by its id or its tuple
         (type, url).
 
@@ -1184,8 +1133,6 @@
             ValueError: if the keys does not match (url and type) nor id.
 
         """
-        db = self.db
-
         origin_id = origin.get('id')
         if origin_id:  # check lookup per id first
             ori = db.origin_get(origin_id, cur)
@@ -1200,7 +1147,7 @@
 
     @db_transaction_generator
     def origin_search(self, url_pattern, offset=0, limit=50,
-                      regexp=False, cur=None):
+                      regexp=False, db=None, cur=None):
         """Search for origins whose urls contain a provided string pattern
         or match a provided regular expression.
         The search is performed in a case insensitive way.
@@ -1216,14 +1163,12 @@
             An iterable of dict containing origin information as returned
             by :meth:`swh.storage.storage.Storage.origin_get`.
         """
-        db = self.db
-
         for origin in db.origin_search(url_pattern, offset, limit,
                                        regexp, cur):
             yield dict(zip(self.origin_keys, origin))
 
     @db_transaction
-    def _person_add(self, person, cur=None):
+    def _person_add(self, person, db=None, cur=None):
         """Add a person in storage.
 
         Note: Internal function for now, do not use outside of this module.
@@ -1238,12 +1183,10 @@
             Id of the new person.
 
         """
-        db = self.db
-
         return db.person_add(person)
 
     @db_transaction_generator
-    def person_get(self, person, cur=None):
+    def person_get(self, person, db=None, cur=None):
         """Return the persons identified by their ids.
 
         Args:
@@ -1253,13 +1196,11 @@
             The array of persons corresponding of the ids.
 
         """
-        db = self.db
-
         for person in db.person_get(person):
             yield dict(zip(db.person_get_cols, person))
 
     @db_transaction
-    def origin_add(self, origins, cur=None):
+    def origin_add(self, origins, db=None, cur=None):
         """Add origins to the storage
 
         Args:
@@ -1276,12 +1217,12 @@
 
         ret = []
         for origin in origins:
-            ret.append(self.origin_add_one(origin, cur=cur))
+            ret.append(self.origin_add_one(origin, db=db, cur=cur))
 
         return ret
 
     @db_transaction
-    def origin_add_one(self, origin, cur=None):
+    def origin_add_one(self, origin, db=None, cur=None):
         """Add origin to the storage
 
         Args:
@@ -1296,8 +1237,6 @@
             exists.
 
         """
-        db = self.db
-
         data = db.origin_get_with(origin['type'], origin['url'], cur)
         if data:
             return data[0]
@@ -1305,7 +1244,7 @@
         return db.origin_add(origin['type'], origin['url'], cur)
 
     @db_transaction
-    def fetch_history_start(self, origin_id, cur=None):
+    def fetch_history_start(self, origin_id, db=None, cur=None):
         """Add an entry for origin origin_id in fetch_history. Returns the id
         of the added fetch_history entry
         """
@@ -1314,15 +1253,15 @@
             'date': datetime.datetime.now(tz=datetime.timezone.utc),
         }
 
-        return self.db.create_fetch_history(fetch_history, cur)
+        return db.create_fetch_history(fetch_history, cur)
 
     @db_transaction
-    def fetch_history_end(self, fetch_history_id, data, cur=None):
+    def fetch_history_end(self, fetch_history_id, data, db=None, cur=None):
         """Close the fetch_history entry with id `fetch_history_id`, replacing
            its data with `data`.
         """
         now = datetime.datetime.now(tz=datetime.timezone.utc)
-        fetch_history = self.db.get_fetch_history(fetch_history_id, cur)
+        fetch_history = db.get_fetch_history(fetch_history_id, cur)
 
         if not fetch_history:
             raise ValueError('No fetch_history with id %d' % fetch_history_id)
@@ -1331,16 +1270,16 @@
 
         fetch_history.update(data)
 
-        self.db.update_fetch_history(fetch_history, cur)
+        db.update_fetch_history(fetch_history, cur)
 
     @db_transaction
-    def fetch_history_get(self, fetch_history_id, cur=None):
+    def fetch_history_get(self, fetch_history_id, db=None, cur=None):
         """Get the fetch_history entry with id `fetch_history_id`.
         """
-        return self.db.get_fetch_history(fetch_history_id, cur)
+        return db.get_fetch_history(fetch_history_id, cur)
 
     @db_transaction
-    def entity_add(self, entities, cur=None):
+    def entity_add(self, entities, db=None, cur=None):
         """Add the given entitites to the database (in entity_history).
 
         Args:
@@ -1363,8 +1302,6 @@
                   listed the entity.
 
         """
-        db = self.db
-
         cols = list(db.entity_history_cols)
         cols.remove('id')
 
@@ -1373,7 +1310,7 @@
         db.entity_history_add_from_temp()
 
     @db_transaction_generator
-    def entity_get_from_lister_metadata(self, entities, cur=None):
+    def entity_get_from_lister_metadata(self, entities, db=None, cur=None):
         """Fetch entities from the database, matching with the lister and
            associated metadata.
 
@@ -1387,8 +1324,6 @@
 
         """
 
-        db = self.db
-
         db.mktemp_entity_lister(cur)
 
         mapped_entities = []
@@ -1418,7 +1353,7 @@
                 }
 
     @db_transaction_generator
-    def entity_get(self, uuid, cur=None):
+    def entity_get(self, uuid, db=None, cur=None):
         """Returns the list of entity per its uuid identifier and also its
         parent hierarchy.
 
@@ -1430,12 +1365,11 @@
             hierarchy from such entity.
 
         """
-        db = self.db
         for entity in db.entity_get(uuid, cur):
             yield dict(zip(db.entity_cols, entity))
 
     @db_transaction
-    def entity_get_one(self, uuid, cur=None):
+    def entity_get_one(self, uuid, db=None, cur=None):
         """Returns one entity using its uuid identifier.
 
         Args:
@@ -1445,7 +1379,6 @@
             the object corresponding to the given entity
 
         """
-        db = self.db
         entity = db.entity_get_one(uuid, cur)
         if entity:
             return dict(zip(db.entity_cols, entity))
@@ -1453,7 +1386,7 @@
             return None
 
     @db_transaction
-    def stat_counters(self, cur=None):
+    def stat_counters(self, db=None, cur=None):
         """compute statistics about the number of tuples in various tables
 
         Returns:
@@ -1461,11 +1394,11 @@
             integer values (e.g., the number of tuples in table content)
 
         """
-        return {k: v for (k, v) in self.db.stat_counters()}
+        return {k: v for (k, v) in db.stat_counters()}
 
     @db_transaction
     def origin_metadata_add(self, origin_id, ts, provider, tool, metadata,
-                            cur=None):
+                            db=None, cur=None):
         """ Add an origin_metadata for the origin at ts with provenance and
         metadata.
 
@@ -1482,11 +1415,12 @@
         if isinstance(ts, str):
             ts = dateutil.parser.parse(ts)
 
-        return self.db.origin_metadata_add(origin_id, ts, provider, tool,
-                                           metadata, cur)
+        return db.origin_metadata_add(origin_id, ts, provider, tool,
+                                      metadata, cur)
 
     @db_transaction_generator
-    def origin_metadata_get_by(self, origin_id, provider_type=None, cur=None):
+    def origin_metadata_get_by(self, origin_id, provider_type=None, db=None,
+                               cur=None):
         """Retrieve list of all origin_metadata entries for the origin_id
 
         Args:
@@ -1507,12 +1441,11 @@
             - provider_url (str)
 
         """
-        db = self.db
         for line in db.origin_metadata_get_by(origin_id, provider_type, cur):
             yield dict(zip(db.origin_metadata_get_cols, line))
 
     @db_transaction_generator
-    def tool_add(self, tools, cur=None):
+    def tool_add(self, tools, db=None, cur=None):
         """Add new tools to the storage.
 
         Args:
@@ -1530,7 +1463,6 @@
             guaranteed to match the order of the initial list.
 
         """
-        db = self.db
         db.mktemp_tool(cur)
         db.copy_to(tools, 'tmp_tool',
                    ['name', 'version', 'configuration'],
@@ -1541,7 +1473,7 @@
             yield dict(zip(db.tool_cols, line))
 
     @db_transaction
-    def tool_get(self, tool, cur=None):
+    def tool_get(self, tool, db=None, cur=None):
         """Retrieve tool information.
 
         Args:
@@ -1553,7 +1485,6 @@
             None otherwise.
 
         """
-        db = self.db
         tool_conf = tool['configuration']
         if isinstance(tool_conf, dict):
             tool_conf = json.dumps(tool_conf)
@@ -1563,31 +1494,28 @@
                           tool_conf)
         if not idx:
             return None
-        return dict(zip(self.db.tool_cols, idx))
+        return dict(zip(db.tool_cols, idx))
 
     @db_transaction
     def metadata_provider_add(self, provider_name, provider_type, provider_url,
-                              metadata, cur=None):
-        db = self.db
+                              metadata, db=None, cur=None):
         return db.metadata_provider_add(provider_name, provider_type,
                                         provider_url, metadata, cur)
 
     @db_transaction
-    def metadata_provider_get(self, provider_id, cur=None):
-        db = self.db
+    def metadata_provider_get(self, provider_id, db=None, cur=None):
         result = db.metadata_provider_get(provider_id)
         if not result:
             return None
-        return dict(zip(self.db.metadata_provider_cols, result))
+        return dict(zip(db.metadata_provider_cols, result))
 
     @db_transaction
-    def metadata_provider_get_by(self, provider, cur=None):
-        db = self.db
+    def metadata_provider_get_by(self, provider, db=None, cur=None):
         result = db.metadata_provider_get_by(provider['provider_name'],
                                              provider['provider_url'])
         if not result:
             return None
-        return dict(zip(self.db.metadata_provider_cols, result))
+        return dict(zip(db.metadata_provider_cols, result))
 
     def diff_directories(self, from_dir, to_dir, track_renaming=False):
         """Compute the list of file changes introduced between two arbitrary
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
@@ -2483,7 +2483,7 @@
 
         self.storage.content_update([cont], keys=['sha1_git'])
 
-        with self.storage.db.transaction() as cur:
+        with self.storage.get_db().transaction() as cur:
             cur.execute('SELECT sha1, sha1_git, sha256, length, status'
                         ' FROM content WHERE sha1 = %s',
                         (cont['sha1'],))
@@ -2497,7 +2497,7 @@
 
     @istest
     def content_update_with_new_cols(self):
-        with self.storage.db.transaction() as cur:
+        with self.storage.get_db().transaction() as cur:
             cur.execute("""alter table content
                            add column test text default null,
                            add column test2 text default null""")
@@ -2508,7 +2508,7 @@
         cont['test2'] = 'value-2'
 
         self.storage.content_update([cont], keys=['test', 'test2'])
-        with self.storage.db.transaction() as cur:
+        with self.storage.get_db().transaction() as cur:
             cur.execute(
                 'SELECT sha1, sha1_git, sha256, length, status, test, test2'
                 ' FROM content WHERE sha1 = %s',
@@ -2522,6 +2522,6 @@
             (cont['sha1'], cont['sha1_git'], cont['sha256'],
              cont['length'], 'visible', cont['test'], cont['test2']))
 
-        with self.storage.db.transaction() as cur:
+        with self.storage.get_db().transaction() as cur:
             cur.execute("""alter table content drop column test,
                            drop column test2""")