use new pool when configuration is reloaded

src/PostgREST/AppState.hs

@@ -83,7 +83,7 @@ data AuthResult = AuthResult
 
 data AppState = AppState
   -- | Database connection pool
-  { statePool                     :: SQL.Pool
+  { statePool                     :: IORef SQL.Pool
   -- | Database server version, will be updated by the connectionWorker
   , statePgVersion                :: IORef PgVersion
   -- | No schema cache at the start. Will be filled in by the connectionWorker
@@ -125,8 +125,9 @@ init conf = do
 
 initWithPool :: AppSockets -> SQL.Pool -> AppConfig -> IO AppState
 initWithPool (sock, adminSock) pool conf = do
-  appState <- AppState pool
-    <$> newIORef minimumPgVersion -- assume we're in a supported version when starting, this will be corrected on a later step
+  appState <- AppState
+    <$> newIORef pool
+    <*> newIORef minimumPgVersion -- assume we're in a supported version when starting, this will be corrected on a later step
     <*> newIORef Nothing
     <*> pure (pure ())
     <*> newEmptyMVar
@@ -208,7 +209,8 @@ initPool AppConfig{..} =
 -- | Run an action with a database connection.
 usePool :: AppState -> AppConfig -> SQL.Session a -> IO (Either SQL.UsageError a)
 usePool appState@AppState{..} AppConfig{configLogLevel} x = do
-  res <- SQL.use statePool x
+  pool <- getPool appState
+  res <- SQL.use pool x
 
   when (configLogLevel > LogCrit) $ do
     whenLeft res (\case
@@ -223,11 +225,17 @@ usePool appState@AppState{..} AppConfig{configLogLevel} x = do
 -- | Flush the connection pool so that any future use of the pool will
 -- use connections freshly established after this call.
 flushPool :: AppState -> IO ()
-flushPool AppState{..} = SQL.release statePool
+flushPool appState = SQL.release =<< getPool appState
 
 -- | Destroy the pool on shutdown.
 destroyPool :: AppState -> IO ()
-destroyPool AppState{..} = SQL.release statePool
+destroyPool appState = SQL.release =<< getPool appState
+
+getPool :: AppState -> IO SQL.Pool
+getPool = readIORef . statePool
+
+putPool :: AppState -> SQL.Pool -> IO ()
+putPool = atomicWriteIORef . statePool
 
 getPgVersion :: AppState -> IO PgVersion
 getPgVersion = readIORef . statePgVersion
@@ -478,6 +486,7 @@ reReadConfig startingUp appState = do
         logWithZTime appState $ "Failed reloading config: " <> err
     Right newConf -> do
       putConfig appState newConf
+      putPool appState =<< initPool newConf
       if startingUp then
         pass
       else

test/io/fixtures.sql

@@ -198,3 +198,11 @@ $$ language sql set statement_timeout = '4s';
 create function get_postgres_version() returns int as $$
   select current_setting('server_version_num')::int;
 $$ language sql;
+
+create function change_db_pool_config(size int) returns void as $_$
+begin
+  execute format($$
+    alter role postgrest_test_authenticator set pgrst.db_pool = %L;
+  $$, size);
+  perform pg_notify('pgrst', 'reload config');
+end $_$ volatile security definer language plpgsql;

test/io/test_io.py

@@ -582,6 +582,42 @@ def test_pool_acquisition_timeout(level, defaultenv, metapostgrest):
             assert "Timed out acquiring connection from connection pool." in output[1]
 
 
+def test_db_pool_configuration_reload(defaultenv):
+    "Verify that PGRST_DB_POOL setting is reloaded correctly"
+
+    env = {
+        **defaultenv,
+        "PGRST_DB_POOL": "1",
+        "PGRST_DB_POOL_ACQUISITION_TIMEOUT": "1",  # 1 second
+    }
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.post(
+            "/rpc/change_db_pool_config", data={"size": 2}
+        )
+        assert response.status_code == 204
+
+        sleep_until_postgrest_config_reload()
+
+        def sleep():
+            res = postgrest.session.get("/rpc/sleep?seconds=1")
+            assert res.status_code == 204
+
+        def get_projects():
+            res = postgrest.session.get("/projects")
+            assert res.status_code == 200
+
+        thread_1 = Thread(target=sleep)
+        thread_1.start()
+
+        # This would return an error if the DB_POOL is only 1
+        thread_2 = Thread(target=get_projects)
+        thread_2.start()
+
+        thread_1.join()
+        thread_2.join()
+
+
 def test_change_statement_timeout_held_connection(defaultenv, metapostgrest):
     "Statement timeout changes take effect immediately, even with a request outliving the reconfiguration"