Fix race for concurrent downloads of remote media. (#8682)

Fixes #6755

synapse/storage/databases/main/media_repository.py

@@ -452,6 +452,33 @@ class MediaRepositoryStore(MediaRepositoryBackgroundUpdateStore):
             desc="get_remote_media_thumbnails",
         )
 
+    async def get_remote_media_thumbnail(
+        self, origin: str, media_id: str, t_width: int, t_height: int, t_type: str,
+    ) -> Optional[Dict[str, Any]]:
+        """Fetch the thumbnail info of given width, height and type.
+        """
+
+        return await self.db_pool.simple_select_one(
+            table="remote_media_cache_thumbnails",
+            keyvalues={
+                "media_origin": origin,
+                "media_id": media_id,
+                "thumbnail_width": t_width,
+                "thumbnail_height": t_height,
+                "thumbnail_type": t_type,
+            },
+            retcols=(
+                "thumbnail_width",
+                "thumbnail_height",
+                "thumbnail_method",
+                "thumbnail_type",
+                "thumbnail_length",
+                "filesystem_id",
+            ),
+            allow_none=True,
+            desc="get_remote_media_thumbnail",
+        )
+
     async def store_remote_media_thumbnail(
         self,
         origin,