DPE-7726: Use Patroni API for is_restart_pending()

The previous is_restart_pending() waited for long due to the Patroni's
loop_wait default value (10 seconds), which tells how much time
Patroni will wait before checking the configuration file again to reload it.

Instead of checking PostgreSQL pending_restart from pg_settings,
let's check Patroni API pending_restart=True flag.

Author: taurus-forever

lib/charms/postgresql_k8s/v1/postgresql.py

@@ -1322,23 +1322,6 @@ def update_user_password(
             if connection is not None:
                 connection.close()
 
-    def is_restart_pending(self) -> bool:
-        """Query pg_settings for pending restart."""
-        connection = None
-        try:
-            with self._connect_to_database() as connection, connection.cursor() as cursor:
-                cursor.execute("SELECT COUNT(*) FROM pg_settings WHERE pending_restart=True;")
-                return cursor.fetchone()[0] > 0
-        except psycopg2.OperationalError:
-            logger.warning("Failed to connect to PostgreSQL.")
-            return False
-        except psycopg2.Error as e:
-            logger.error(f"Failed to check if restart is pending: {e}")
-            return False
-        finally:
-            if connection:
-                connection.close()
-
     def database_exists(self, db: str) -> bool:
         """Check whether specified database exists."""
         connection = None

src/charm.py

@@ -2473,18 +2473,11 @@ def _handle_postgresql_restart_need(self) -> None:
             self._patroni.reload_patroni_configuration()
         except Exception as e:
             logger.error(f"Reload patroni call failed! error: {e!s}")
-        # Wait for some more time than the Patroni's loop_wait default value (10 seconds),
-        # which tells how much time Patroni will wait before checking the configuration
-        # file again to reload it.
-        try:
-            for attempt in Retrying(stop=stop_after_attempt(5), wait=wait_fixed(3)):
-                with attempt:
-                    restart_postgresql = restart_postgresql or self.postgresql.is_restart_pending()
-                    if not restart_postgresql:
-                        raise Exception
-        except RetryError:
-            # Ignore the error, as it happens only to indicate that the configuration has not changed.
-            pass
+
+        restart_pending = self._patroni.is_restart_pending()
+        logger.debug(f"Checking if restart pending: {restart_postgresql} or {restart_pending}")
+        restart_postgresql = restart_postgresql or restart_pending
+
         self.unit_peer_data.update({"tls": "enabled" if self.is_tls_enabled else ""})
         self.postgresql_client_relation.update_endpoints()
 

src/cluster.py

@@ -464,6 +464,23 @@ def get_patroni_health(self) -> dict[str, str]:
 
         return r.json()
 
+    def is_restart_pending(self) -> bool:
+        """Returns whether the Patroni/PostgreSQL restart pending."""
+        patroni_status = requests.get(
+            f"{self._patroni_url}/patroni",
+            verify=self.verify,
+            timeout=API_REQUEST_TIMEOUT,
+            auth=self._patroni_auth,
+        )
+        try:
+            pending_restart = patroni_status.json()["pending_restart"]
+        except KeyError:
+            pending_restart = False
+            pass
+        logger.debug(f"Patroni API is_restart_pending: {pending_restart}")
+
+        return pending_restart
+
     @property
     def is_creating_backup(self) -> bool:
         """Returns whether a backup is being created."""