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

See #2848.

Author: meisterT

Diff for: webapp/src/Controller/Jury/JuryMiscController.php

@@ -49,6 +49,13 @@ public function __construct(
     #[Route(path: '', name: 'jury_index')]
     public function indexAction(ConfigurationService $config): Response
     {
+        if ($this->isGranted('ROLE_ADMIN')) {
+            $innodbSnapshotIsolation = $this->em->getConnection()->query('SHOW VARIABLES LIKE "innodb_snapshot_isolation"')->fetchAssociative();
+            if ($innodbSnapshotIsolation && $innodbSnapshotIsolation['Value'] === 'ON') {
+                $this->addFlash('danger', 'InnoDB snapshot isolation is enabled. Set --innodb_snapshot_isolation=OFF 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,

Diff for: webapp/src/Service/CheckConfigService.php

@@ -198,12 +198,16 @@ public function checkMysqlSettings(): ConfigCheckItem
         $r = $this->em->getConnection()->fetchAllAssociative(
             'SHOW variables WHERE Variable_name IN
                  ("innodb_log_file_size", "max_connections", "max_allowed_packet",
-                  "tx_isolation", "transaction_isolation")'
+                  "tx_isolation", "transaction_isolation", "innodb_snapshot_isolation")'
         );
+
         $vars = [];
         foreach ($r as $row) {
             $vars[$row['Variable_name']] = $row['Value'];
         }
+        if (!isset($vars['innodb_snapshot_isolation'])) {
+            $vars['innodb_snapshot_isolation'] = false;
+        }
         # MySQL 8 has "transaction_isolation" instead of "tx_isolation".
         if (isset($vars['transaction_isolation'])) {
             $vars['tx_isolation'] = $vars['transaction_isolation'];
@@ -251,6 +255,13 @@ public function checkMysqlSettings(): ConfigCheckItem
             $desc .= sprintf("max_allowed_packet is set to %s.\n", Utils::printsize((int)$vars['max_allowed_packet']));
         }
 
+        if ($vars['innodb_snapshot_isolation'] === 'ON') {
+            $result = 'E';
+            $desc .= 'InnoDB snapshot isolation is enabled. Set --innodb_snapshot_isolation=OFF in your MariaDB configuration. See https://github.com/DOMjudge/domjudge/issues/2848 for more information.';
+        } else {
+            $desc .= "InnoDB snapshot isolation is disabled.\n";
+        }
+
         $this->stopwatch->stop(__FUNCTION__);
         return new ConfigCheckItem(
             caption: 'MySQL settings',