Issue #2733675 by smccabe, murilohp, andregp, Johnny Santos, ankithashetty, mglaman, jonathanshaw, daffie, alexpott, catch, froboy: Warning when mysql is not set to READ-COMMITTED

(cherry picked from commit 70d480ab7f)

core/assets/scaffold/files/default.settings.php

@@ -138,6 +138,21 @@ $databases = [];
  * request as needed.  The fourth line creates a new database with a name of
  * "extra".
  *
+ * For MySQL, MariaDB or equivalent databases the 'isolation_level' option can
+ * be set. The recommended transaction isolation level for Drupal sites is
+ * 'READ COMMITTED'. The 'REPEATABLE READ' option is supported but can result
+ * in deadlocks, the other two options are 'READ UNCOMMITTED' and 'SERIALIZABLE'.
+ * They are available but not supported; use them at your own risk. For more
+ * info:
+ * https://dev.mysql.com/doc/refman/5.7/en/innodb-transaction-isolation-levels.html
+ *
+ * On your settings.php, change the isolation level:
+ * @code
+ * $databases['default']['default']['init_commands'] = [
+ *   'isolation_level' => 'SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED',
+ * ];
+ * @endcode
+ *
  * You can optionally set a prefix for all database table names by using the
  * 'prefix' setting. If a prefix is specified, the table name will be prepended
  * with its value. Be sure to use valid database characters only, usually

core/modules/mysql/mysql.install

@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * @file
+ * Install, update and uninstall functions for the mysql module.
+ */
+
+use Drupal\Core\Database\Database;
+
+/**
+ * Implements hook_requirements().
+ */
+function mysql_requirements($phase) {
+  $requirements = [];
+
+  if ($phase === 'runtime') {
+    // Test with MySql databases.
+    if (Database::isActiveConnection()) {
+      $connection = Database::getConnection();
+
+      $query = 'SELECT @@SESSION.tx_isolation';
+      // The database variable "tx_isolation" has been removed in MySQL v8.0 and
+      // has been replaced by "transaction_isolation".
+      // @see https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_tx_isolation
+      if (!$connection->isMariaDb() && version_compare($connection->version(), '8.0.0-AnyName', '>')) {
+        $query = 'SELECT @@SESSION.transaction_isolation';
+      }
+
+      $isolation_level = $connection->query($query)->fetchField();
+
+      if ($isolation_level !== 'READ-COMMITTED') {
+        $requirements['mysql_transaction_level'] = [
+          'title' => t('Database Isolation Level'),
+          'severity' => REQUIREMENT_WARNING,
+          'value' => t('Transaction Isolation Level: @value', ['@value' => $isolation_level]),
+          'description' => t('For the best performance and to minimize locking issues, the READ-COMMITTED transaction isolation level is <a href=":performance_doc">recommended</a>.', [
+            ':performance_doc' => 'https://www.drupal.org/docs/system-requirements/setting-the-mysql-transaction-isolation-level',
+          ]),
+        ];
+      }
+    }
+  }
+
+  return $requirements;
+}

core/modules/mysql/tests/src/Functional/RequirementsTest.php

@@ -0,0 +1,88 @@
+<?php
+
+namespace Drupal\Tests\mysql\Functional;
+
+use Drupal\Core\Database\Database;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests isolation level warning when the config is set in settings.php.
+ *
+ * @group mysql
+ */
+class RequirementsTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['mysql'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // The isolation_level option is only available for MySQL.
+    $connectionInfo = Database::getConnectionInfo();
+    if ($connectionInfo['default']['driver'] !== 'mysql') {
+      $this->markTestSkipped("This test does not support the {$connectionInfo['default']['driver']} database driver.");
+    }
+  }
+
+  /**
+   * Test the isolation level warning message on status page.
+   */
+  public function testIsolationLevelWarningNotDisplaying() {
+    $admin_user = $this->drupalCreateUser([
+      'administer site configuration',
+      'access site reports',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Change the isolation level to force the warning message.
+    $this->writeIsolationLevelSettings('REPEATABLE READ');
+
+    // Check if the warning message is being displayed.
+    $this->drupalGet('admin/reports/status');
+    $elements = $this->xpath('//details[@class="system-status-report__entry"]//div[contains(text(), :text)]', [
+      ':text' => 'For the best performance and to minimize locking issues, the READ-COMMITTED',
+    ]);
+    $this->assertCount(1, $elements);
+    $this->assertStringStartsWith('Transaction Isolation Level', $elements[0]->getParent()->getText());
+
+    // Rollback the isolation level to read committed.
+    $this->writeIsolationLevelSettings('READ COMMITTED');
+
+    // Check if the warning message is gone.
+    $this->drupalGet('admin/reports/status');
+    $this->assertSession()->pageTextNotContains('Database Isolation Level');
+    $elements = $this->xpath('//details[@class="system-status-report__entry"]//div[contains(text(), :text)]', [
+      ':text' => 'For the best performance and to minimize locking issues, the READ-COMMITTED',
+    ]);
+
+    $this->assertCount(0, $elements);
+  }
+
+  /**
+   * Writes the isolation level in settings.php.
+   *
+   * @param string $isolation_level
+   *   The isolation level.
+   */
+  private function writeIsolationLevelSettings(string $isolation_level) {
+    $settings['databases']['default']['default']['init_commands'] = (object) [
+      'value'    => [
+        'isolation' => "SET SESSION TRANSACTION ISOLATION LEVEL {$isolation_level}",
+      ],
+      'required' => TRUE,
+    ];
+    $this->writeSettings($settings);
+  }
+
+}

sites/default/default.settings.php

@@ -138,6 +138,21 @@ $databases = [];
  * request as needed.  The fourth line creates a new database with a name of
  * "extra".
  *
+ * For MySQL, MariaDB or equivalent databases the 'isolation_level' option can
+ * be set. The recommended transaction isolation level for Drupal sites is
+ * 'READ COMMITTED'. The 'REPEATABLE READ' option is supported but can result
+ * in deadlocks, the other two options are 'READ UNCOMMITTED' and 'SERIALIZABLE'.
+ * They are available but not supported; use them at your own risk. For more
+ * info:
+ * https://dev.mysql.com/doc/refman/5.7/en/innodb-transaction-isolation-levels.html
+ *
+ * On your settings.php, change the isolation level:
+ * @code
+ * $databases['default']['default']['init_commands'] = [
+ *   'isolation_level' => 'SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED',
+ * ];
+ * @endcode
+ *
  * You can optionally set a prefix for all database table names by using the
  * 'prefix' setting. If a prefix is specified, the table name will be prepended
  * with its value. Be sure to use valid database characters only, usually