2 files changed, 17 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index 20a5ca2baa..25b8aef617 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -38,6 +38,15 @@ module ActiveRecord
         configure_connection
       end
 
+      MAX_INDEX_LENGTH_FOR_UTF8MB4 = 191
+      def initialize_schema_migrations_table
+        if @config[:encoding] == 'utf8mb4'
+          ActiveRecord::SchemaMigration.create_table(MAX_INDEX_LENGTH_FOR_UTF8MB4)
+        else
+          ActiveRecord::SchemaMigration.create_table
+        end
+      end
+
       def supports_explain?
         true
       end
diff --git a/activerecord/lib/active_record/schema_migration.rb b/activerecord/lib/active_record/schema_migration.rb
index 9830abe7d8..6077144265 100644
--- a/activerecord/lib/active_record/schema_migration.rb
+++ b/activerecord/lib/active_record/schema_migration.rb
@@ -13,18 +13,21 @@ module ActiveRecord
       "#{Base.table_name_prefix}unique_schema_migrations#{Base.table_name_suffix}"
     end
 
-    def self.create_table
+    def self.create_table(limit=nil)
       unless connection.table_exists?(table_name)
-        connection.create_table(table_name, :id => false) do |t|
-          t.column :version, :string, :null => false
+        version_options = {null: false}
+        version_options[:limit] = limit if limit
+
+        connection.create_table(table_name, id: false) do |t|
+          t.column :version, :string, version_options
         end
-        connection.add_index table_name, :version, :unique => true, :name => index_name
+        connection.add_index table_name, :version, unique: true, name: index_name
       end
     end
 
     def self.drop_table
       if connection.table_exists?(table_name)
-        connection.remove_index table_name, :name => index_name
+        connection.remove_index table_name, name: index_name
         connection.drop_table(table_name)
       end
     end