transaction-events.patch

diff --git a/core/lib/Drupal/Core/Database/Connection.php b/core/lib/Drupal/Core/Database/Connection.php
index 2002e9e..c3b0d7e 100644
--- a/core/lib/Drupal/Core/Database/Connection.php
+++ b/core/lib/Drupal/Core/Database/Connection.php
@@ -1092,6 +1092,10 @@ public function rollback($savepoint_name = 'drupal_transaction') {
         if ($rolled_back_other_active_savepoints) {
           throw new TransactionOutOfOrderException();
         }
+
+        // Dispatch event for transaction rollback.
+        $event = new TransactionEvent($savepoint, $this);
+        \Drupal::service('event_dispatcher')->dispatch(DatabaseEvents::ROLLBACK, $event);
         return;
       }
       else {
@@ -1102,6 +1106,11 @@ public function rollback($savepoint_name = 'drupal_transaction') {
     if ($rolled_back_other_active_savepoints) {
       throw new TransactionOutOfOrderException();
     }
+    else {
+      // Dispatch event for transaction rollback.
+      $event = new TransactionEvent($savepoint, $this);
+      \Drupal::service('event_dispatcher')->dispatch(DatabaseEvents::ROLLBACK, $event);
+    }
   }
 
   /**
@@ -1132,6 +1141,10 @@ public function pushTransaction($name) {
       $this->connection->beginTransaction();
     }
     $this->transactionLayers[$name] = $name;
+
+    // Dispatch event for transaction begin.
+    $event = new TransactionEvent($name, $this);
+    \Drupal::service('event_dispatcher')->dispatch(DatabaseEvents::START_TRANSACTION, $event);
   }
 
   /**
@@ -1179,6 +1192,7 @@ protected function popCommittableTransactions() {
 
       // If there are no more layers left then we should commit.
       unset($this->transactionLayers[$name]);
+
       if (empty($this->transactionLayers)) {
         if (!$this->connection->commit()) {
           throw new TransactionCommitFailedException();
@@ -1187,6 +1201,11 @@ protected function popCommittableTransactions() {
       else {
         $this->query('RELEASE SAVEPOINT ' . $name);
       }
+
+      // Dispatch event for transaction commit.
+      $event = new TransactionEvent($name, $this);
+      $dispatcher = \Drupal::service('event_dispatcher');
+      $dispatcher->dispatch(DatabaseEvents::COMMIT, $event);
     }
   }
 
diff --git a/core/lib/Drupal/Core/Database/DatabaseEvents.php b/core/lib/Drupal/Core/Database/DatabaseEvents.php
new file mode 100644
index 0000000..91c06ce
--- /dev/null
+++ b/core/lib/Drupal/Core/Database/DatabaseEvents.php
@@ -0,0 +1,60 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Database\DatabaseEvents.
+ */
+
+namespace Drupal\Core\Database;
+
+/**
+ * Contains all events thrown while performing database actions.
+ */
+final class DatabaseEvents {
+
+  /**
+   * The name of the event triggered when a transaction is started.
+   *
+   * This event allows modules to react to a transaction being started. The
+   * event listener method receives a \Drupal\Core\Database\TransactionEvent
+   * instance.
+   *
+   * @Event
+   *
+   * @see \Drupal\Core\Database\TransactionEvent
+   *
+   * @var string
+   */
+  const START_TRANSACTION = 'database.transaction.start';
+
+  /**
+   * The name of the event triggered when a transaction is committed.
+   *
+   * This event allows modules to react to a transaction being committed. The
+   * event listener method receives a \Drupal\Core\Database\TransactionEvent
+   * instance.
+   *
+   * @Event
+   *
+   * @see \Drupal\Core\Database\TransactionEvent
+   *
+   * @var string
+   */
+  const COMMIT = 'database.transaction.commit';
+
+  /**
+   * The name of the event triggered when a transaction is rolled back.
+   *
+   * This event allows modules to react to a transaction being rolled back. The
+   * event listener method receives a \Drupal\Core\Database\TransactionEvent
+   * instance.
+   *
+   * @Event
+   *
+   * @see \Drupal\Core\Database\TransactionEvent
+   *
+   * @var string
+   */
+  const ROLLBACK = 'database.transaction.rollback';
+
+}
diff --git a/core/lib/Drupal/Core/Database/Driver/mysql/Connection.php b/core/lib/Drupal/Core/Database/Driver/mysql/Connection.php
index dead7ab..7344e5b 100644
--- a/core/lib/Drupal/Core/Database/Driver/mysql/Connection.php
+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Connection.php
@@ -5,8 +5,10 @@
 use Drupal\Core\Database\DatabaseExceptionWrapper;
 
 use Drupal\Core\Database\Database;
+use Drupal\Core\Database\DatabaseEvents;
 use Drupal\Core\Database\DatabaseNotFoundException;
 use Drupal\Core\Database\TransactionCommitFailedException;
+use Drupal\Core\Database\TransactionEvent;
 use Drupal\Core\Database\DatabaseException;
 use Drupal\Core\Database\Connection as DatabaseConnection;
 use Drupal\Component\Utility\Unicode;
@@ -325,6 +327,10 @@ protected function popCommittableTransactions() {
           }
         }
       }
+
+      // Dispatch event for transaction commit.
+      $event = new TransactionEvent($name, $this);
+      \Drupal::service('event_dispatcher')->dispatch(DatabaseEvents::COMMIT, $event);
     }
   }
 
diff --git a/core/lib/Drupal/Core/Database/TransactionEvent.php b/core/lib/Drupal/Core/Database/TransactionEvent.php
new file mode 100644
index 0000000..b7756fc
--- /dev/null
+++ b/core/lib/Drupal/Core/Database/TransactionEvent.php
@@ -0,0 +1,65 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Database\TransactionEvent.
+ */
+
+namespace Drupal\Core\Database;
+
+use Symfony\Component\EventDispatcher\GenericEvent;
+use Drupal\Core\Database\Connection as DatabaseConnection;
+
+/**
+ * Defines a base class for all database transaction events.
+ */
+class TransactionEvent extends GenericEvent {
+
+  /**
+   * The name of the transaction started/ended.
+   *
+   * @var int
+   */
+  protected $transactionName;
+
+  /**
+   * The connection the event occurred on.
+   *
+   * @var int
+   */
+  protected $databaseConnection;
+
+  /**
+   * Constructs a new TransactionEvent.
+   *
+   * @param string $transaction_name
+   *   The name of the transaction started/ended.
+   * @param DatabaseConnection $database_connection
+   *   The depth of the transaction started/ended.
+   */
+  public function __construct($transaction_name, DatabaseConnection $database_connection) {
+    $this->transactionName = $transaction_name;
+    $this->databaseConnection = $database_connection;
+  }
+
+  /**
+   * The name of the transaction started/ended.
+   *
+   * @return int
+   *   The name of the transaction started/ended.
+   */
+  public function getTransactionName() {
+    return $this->transactionName;
+  }
+
+  /**
+   * The database connection the event occurred on.
+   *
+   * @return \Drupal\Core\Database\Connection
+   *   The database connection object.
+   */
+  public function getDatabaseConnection() {
+    return $this->databaseConnection;
+  }
+
+}