Add a warning if --innodb_snapshot_isolation=true is set.

See #2848.

Author: meisterT

webapp/src/Controller/Jury/JuryMiscController.php

@@ -49,6 +49,11 @@ public function __construct(
     #[Route(path: '', name: 'jury_index')]
     public function indexAction(ConfigurationService $config): Response
     {
+        $innodbSnapshotIsolation = $this->em->getConnection()->query('SHOW VARIABLES LIKE "innodb_snapshot_isolation"')->fetchOne();
+        if ($innodbSnapshotIsolation) {
+            $this->addFlash('danger', 'InnoDB snapshot isolation is enabled. Set --innodb_snapshot_isolation=false in your MariaDB configuration. See https://github.com/DOMjudge/domjudge/issues/2848 for more information.');
+        }
+
         return $this->render('jury/index.html.twig', [
             'adminer_enabled' => $config->get('adminer_enabled'),
             'CCS_SPEC_API_URL' => GI::CCS_SPEC_API_URL,