diff --git a/reana_workflow_controller/workflow_run_manager.py b/reana_workflow_controller/workflow_run_manager.py
index 3eee0b93..575b94a7 100644
--- a/reana_workflow_controller/workflow_run_manager.py
+++ b/reana_workflow_controller/workflow_run_manager.py
@@ -600,6 +600,8 @@ def _create_job_spec(
                     "name": "REANA_SQLALCHEMY_DATABASE_URI",
                     "value": SQLALCHEMY_DATABASE_URI,
                 },
+                # reduce the number of open database connections kept in the pool
+                {"name": "SQLALCHEMY_POOL_SIZE", "value": "1"},
                 {"name": "REANA_STORAGE_BACKEND", "value": REANA_STORAGE_BACKEND},
                 {"name": "REANA_COMPONENT_PREFIX", "value": REANA_COMPONENT_PREFIX},
                 {