only in patch2:
unchanged:
--- a/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
+++ b/core/modules/migrate/src/Plugin/migrate/id_map/Sql.php
@@ -261,6 +261,12 @@ protected function ensureTables() {
       foreach ($this->migration->getSourcePlugin()->getIds() as $id_definition) {
         $mapkey = 'sourceid' . $count++;
         $source_id_schema[$mapkey] = $this->getFieldSchema($id_definition);
+
+        // With InnoDB, utf8mb4-based primary keys can't be over 191 characters.
+        // Use ASCII-based primary keys instead.
+        if (isset($source_id_schema[$mapkey]['type']) && $source_id_schema[$mapkey]['type'] == 'varchar') {
+          $source_id_schema[$mapkey]['type'] = 'varchar_ascii';
+        }
         $pks[] = $mapkey;
       }
 
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Tests/Table/d6/System.php
+++ b/core/modules/migrate_drupal/src/Tests/Table/d6/System.php
@@ -6,7 +6,7 @@
  *
  * THIS IS A GENERATED FILE. DO NOT EDIT.
  *
- * @see cores/scripts/dump-database-d6.sh
+ * @see core/scripts/dump-database-d6.sh
  * @see https://www.drupal.org/sandbox/benjy/2405029
  */
 
@@ -26,7 +26,7 @@ public function load() {
       ),
       'fields' => array(
         'filename' => array(
-          'type' => 'varchar',
+          'type' => 'varchar_ascii',
           'not null' => TRUE,
           'length' => '255',
           'default' => '',
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/database_test/database_test.install
+++ b/core/modules/system/tests/modules/database_test/database_test.install
@@ -24,7 +24,7 @@ function database_test_schema() {
       ),
       'name' => array(
         'description' => "A person's name",
-        'type' => 'varchar',
+        'type' => 'varchar_ascii',
         'length' => 255,
         'not null' => TRUE,
         'default' => '',
@@ -75,7 +75,7 @@ function database_test_schema() {
       ),
       'job' => array(
         'description' => "The person's job",
-        'type' => 'varchar',
+        'type' => 'varchar_ascii',
         'length' => 255,
         'not null' => TRUE,
         'default' => '',
@@ -106,7 +106,7 @@ function database_test_schema() {
       ),
       'job' => array(
         'description' => "The person's job",
-        'type' => 'varchar',
+        'type' => 'varchar_ascii',
         'length' => 255,
         'not null' => TRUE,
         'default' => '',
@@ -197,7 +197,7 @@ function database_test_schema() {
       ),
       'name' => array(
         'description' => "A person's name.",
-        'type' => 'varchar',
+        'type' => 'varchar_ascii',
         'length' => 255,
         'not null' => FALSE,
         'default' => '',
only in patch2:
unchanged:
--- a/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestStringId.php
+++ b/core/modules/system/tests/modules/entity_test/src/Entity/EntityTestStringId.php
@@ -45,7 +45,10 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
     $fields['id'] = BaseFieldDefinition::create('string')
       ->setLabel(t('ID'))
       ->setDescription(t('The ID of the test entity.'))
-      ->setReadOnly(TRUE);
+      ->setReadOnly(TRUE)
+      // In order to work around the InnoDB 191 character limit on utf8mb4
+      // primary keys, we set the character set for the field to ASCII.
+      ->setSetting('is_ascii', TRUE);
     return $fields;
   }
 
only in patch2:
unchanged:
--- a/core/modules/views/src/Tests/ViewTestData.php
+++ b/core/modules/views/src/Tests/ViewTestData.php
@@ -75,7 +75,7 @@ public static function schemaDefinition() {
         ),
         'name' => array(
           'description' => "A person's name",
-          'type' => 'varchar',
+          'type' => 'varchar_ascii',
           'length' => 255,
           'not null' => TRUE,
           'default' => '',
only in patch2:
unchanged:
--- a/core/scripts/dump-database-d6.sh
+++ b/core/scripts/dump-database-d6.sh
@@ -52,7 +52,11 @@
 // Get the current schema, order it by table name.
 $schema = drupal_get_schema();
 ksort($schema);
-
+// Override the field type of the filename primary key to bypass the
+// InnoDB 191 character limitation.
+if ($schema['system']['primary key'] == 'filename' && $schema['system']['fields']['filename']['type'] == 'varchar') {
+  $schema['system']['fields']['filename']['type'] = 'varchar_ascii';
+}
 // Export all the tables in the schema.
 foreach ($schema as $table => $data) {
   // Remove descriptions to save time and code.
only in patch2:
unchanged:
--- a/core/tests/Drupal/Tests/Core/Routing/RoutingFixtures.php
+++ b/core/tests/Drupal/Tests/Core/Routing/RoutingFixtures.php
@@ -176,7 +176,7 @@ public function routingTableDefinition() {
       'fields' => array(
         'name' => array(
           'description' => 'Primary Key: Machine name of this route',
-          'type' => 'varchar',
+          'type' => 'varchar_ascii',
           'length' => 255,
           'not null' => TRUE,
           'default' => '',