diff --git a/swh/provenance/postgresql/archive.py b/swh/provenance/postgresql/archive.py
index 632a841..0e4c05f 100644
--- a/swh/provenance/postgresql/archive.py
+++ b/swh/provenance/postgresql/archive.py
@@ -1,41 +1,41 @@
 import psycopg2
 
 from ..archive import ArchiveInterface
 
 # from functools import lru_cache
+from methodtools import lru_cache
 from typing import List
 
 
 class ArchivePostgreSQL(ArchiveInterface):
     def __init__(self, conn: psycopg2.extensions.connection):
         self.conn = conn
         self.cursor = conn.cursor()
 
-    # @lru_cache
+    @lru_cache(maxsize=None)
     def directory_ls(self, id: bytes):
         self.cursor.execute('''WITH
             dir  AS (SELECT id AS dir_id, dir_entries, file_entries, rev_entries
                     FROM directory WHERE id=%s),
             ls_d AS (SELECT dir_id, unnest(dir_entries) AS entry_id from dir),
             ls_f AS (SELECT dir_id, unnest(file_entries) AS entry_id from dir),
             ls_r AS (SELECT dir_id, unnest(rev_entries) AS entry_id from dir)
             (SELECT 'dir'::directory_entry_type AS type, e.target, e.name, NULL::sha1_git
             FROM ls_d
             LEFT JOIN directory_entry_dir e ON ls_d.entry_id=e.id)
             UNION
             (WITH known_contents AS
             (SELECT 'file'::directory_entry_type AS type, e.target, e.name, c.sha1_git
                 FROM ls_f
                 LEFT JOIN directory_entry_file e ON ls_f.entry_id=e.id
                 INNER JOIN content c ON e.target=c.sha1_git)
             SELECT * FROM known_contents
             UNION
             (SELECT 'file'::directory_entry_type AS type, e.target, e.name, c.sha1_git
                 FROM ls_f
                 LEFT JOIN directory_entry_file e ON ls_f.entry_id=e.id
                 LEFT JOIN skipped_content c ON e.target=c.sha1_git
                 WHERE NOT EXISTS (SELECT 1 FROM known_contents WHERE known_contents.sha1_git=e.target)))
             ORDER BY name
         ''', (id,))
-        for row in self.cursor.fetchall():
-            yield {'type': row[0], 'target': row[1], 'name': row[2]}
+        return [{'type': row[0], 'target': row[1], 'name': row[2]} for row in self.cursor.fetchall()]
diff --git a/swh/provenance/storage/archive.py b/swh/provenance/storage/archive.py
index 531ed55..c96c644 100644
--- a/swh/provenance/storage/archive.py
+++ b/swh/provenance/storage/archive.py
@@ -1,44 +1,45 @@
 import psycopg2
 
 from ..archive import ArchiveInterface
 
 # from functools import lru_cache
+from methodtools import lru_cache
 from typing import List
 from swh.storage import get_storage
 
 
 class ArchiveStorage(ArchiveInterface):
     def __init__(self, cls: str, **kwargs):
         self.storage = get_storage(cls, **kwargs)
 
-    # @lru_cache
+    @lru_cache(maxsize=None)
     def directory_ls(self, id: bytes):
         # TODO: filter unused fields
-        yield from self.storage.directory_ls(id)
+        return [entry for entry in self.storage.directory_ls(id)]
 
     def iter_origins(self):
         from swh.storage.algos.origin import iter_origins
         yield from iter_origins(self.storage)
 
     def iter_origin_visits(self, origin: str):
         from swh.storage.algos.origin import iter_origin_visits
         # TODO: filter unused fields
         yield from iter_origin_visits(self.storage, origin)
 
     def iter_origin_visit_statuses(self, origin: str, visit: int):
         from swh.storage.algos.origin import iter_origin_visit_statuses
         # TODO: filter unused fields
         yield from iter_origin_visit_statuses(self.storage, origin, visit)
 
     def release_get(self, ids: List[bytes]):
         # TODO: filter unused fields
         yield from self.storage.release_get(ids)
 
     def revision_get(self, ids: List[bytes]):
         # TODO: filter unused fields
         yield from self.storage.revision_get(ids)
 
     def snapshot_get_all_branches(self, snapshot: bytes):
         from swh.storage.algos.snapshot import snapshot_get_all_branches
         # TODO: filter unused fields
         return snapshot_get_all_branches(self.storage, snapshot)