Merge branch 'release-v1.20.0' into rav/db_init_logging

synapse/storage/prepare_database.py

@@ -120,6 +120,12 @@ def prepare_database(db_conn, database_engine, config, databases=["main", "state
             )
         else:
             logger.info("%r: Initialising new database", databases)
+
+            # if it's a worker app, refuse to upgrade the database, to avoid multiple
+            # workers doing it at once.
+            if config and config.worker_app is not None:
+                raise UpgradeDatabaseException(EMPTY_DATABASE_ON_WORKER_ERROR)
+
             _setup_new_database(cur, database_engine, databases=databases)
 
         # check if any of our configured dynamic modules want a database