fix: schema cache loading before the in-db config (#3670)

Fixes #3660. Load the config after getting the pg version but before loading the schema.

The regression happened on f09655b.

Also remove schema cache load wrapper and separate db queries in different functions.

Co-authored-by: Laurence Isla <lau.isla.c@gmail.com>

src/PostgREST/AppState.hs

@@ -161,7 +161,7 @@ initWithPool (sock, adminSock) pool conf loggerState metricsState observer = do
   deb <-
     let decisecond = 100000 in
     mkDebounce defaultDebounceSettings
-       { debounceAction = internalSchemaCacheLoad appState
+       { debounceAction = retryingSchemaCacheLoad appState
        , debounceFreq = decisecond
        , debounceEdge = leadingEdge -- runs the worker at the start and the end
        }
@@ -355,13 +355,6 @@ putSCacheStatus = atomicWriteIORef . stateSCacheStatus
 getObserver :: AppState -> ObservationHandler
 getObserver = stateObserver
 
-internalSchemaCacheLoad :: AppState -> IO ()
-internalSchemaCacheLoad appState = do
-  AppConfig{..} <- getConfig appState
-  void $ retryingSchemaCacheLoad appState
-  -- We cannot retry reading the in-db config after it fails immediately, because it could have user errors. We just report the error and continue.
-  when configDbConfig $ readInDbConfig False appState
-
 -- | Try to load the schema cache and retry if it fails.
 --
 -- This is done by repeatedly: 1) flushing the pool, 2) querying the version and validating that the postgres version is supported by us, and 3) loading the schema cache.
@@ -369,16 +362,17 @@ internalSchemaCacheLoad appState = do
 --
 -- + Because connections cache the pg catalog(see #2620)
 -- + For rapid recovery. Otherwise, the pool idle or lifetime timeout would have to be reached for new healthy connections to be acquired.
-retryingSchemaCacheLoad :: AppState -> IO (Maybe PgVersion, Maybe SchemaCache)
+retryingSchemaCacheLoad :: AppState -> IO ()
 retryingSchemaCacheLoad appState@AppState{stateObserver=observer, stateMainThreadId=mainThreadId} =
-  retrying retryPolicy shouldRetry (\RetryStatus{rsIterNumber, rsPreviousDelay} -> do
+  void $ retrying retryPolicy shouldRetry (\RetryStatus{rsIterNumber, rsPreviousDelay} -> do
     when (rsIterNumber > 0) $ do
       let delay = fromMaybe 0 rsPreviousDelay `div` oneSecondInUs
       observer $ ConnectionRetryObs delay
       putNextListenerDelay appState delay
 
     flushPool appState
-    (,) <$> qPgVersion <*> qSchemaCache
+
+    (,) <$> qPgVersion <*> (qInDbConfig *> qSchemaCache)
   )
   where
     qPgVersion :: IO (Maybe PgVersion)
@@ -400,6 +394,11 @@ retryingSchemaCacheLoad appState@AppState{stateObserver=observer, stateMainThrea
           putPgVersion appState actualPgVersion
           return $ Just actualPgVersion
 
+    qInDbConfig :: IO ()
+    qInDbConfig = do
+      AppConfig{..} <- getConfig appState
+      when configDbConfig $ readInDbConfig False appState
+
     qSchemaCache :: IO (Maybe SchemaCache)
     qSchemaCache = do
       conf@AppConfig{..} <- getConfig appState
@@ -438,6 +437,7 @@ retryingSchemaCacheLoad appState@AppState{stateObserver=observer, stateMainThrea
     oneSecondInUs = 1000000 -- one second in microseconds
 
 -- | Reads the in-db config and reads the config file again
+-- | We don't retry reading the in-db config after it fails immediately, because it could have user errors. We just report the error and continue.
 readInDbConfig :: Bool -> AppState -> IO ()
 readInDbConfig startingUp appState@AppState{stateObserver=observer} = do
   AppConfig{..} <- getConfig appState