make some sqlalchemy config options explicit (and not dependent on external specification) because they fundamentally change behaviors

Author: melange396

src/server/_config.py

@@ -11,7 +11,16 @@
 MAX_COMPATIBILITY_RESULTS = int(3650)
 
 SQLALCHEMY_DATABASE_URI = os.environ.get("SQLALCHEMY_DATABASE_URI", "sqlite:///test.db")
-SQLALCHEMY_ENGINE_OPTIONS = json.loads(os.environ.get("SQLALCHEMY_ENGINE_OPTIONS", "{}"))
+
+# defaults
+SQLALCHEMY_ENGINE_OPTIONS = {
+    "pool_pre_ping": True, # enable ping test for validity of recycled pool connections on connect() calls
+    "pool_recycle": 5      # seconds after which a recycled pool connection is considered invalid
+}
+# update with overrides of defaults or additions from external configs
+SQLALCHEMY_ENGINE_OPTIONS.update(
+    json.loads(os.environ.get("SQLALCHEMY_ENGINE_OPTIONS", "{}")))
+
 SECRET = os.environ.get("FLASK_SECRET", "secret")
 URL_PREFIX = os.environ.get("FLASK_PREFIX", "/")