MySQL: `ROW_FORMAT=DYNAMIC` create table option by default

Since MySQL 5.7.9, the `innodb_default_row_format` option defines the
default row format for InnoDB tables. The default setting is `DYNAMIC`.

The row format is required for indexing on `varchar(255)` with `utf8mb4`
columns.

As long as using MySQL 5.6, CI won't be passed even if MySQL server
setting is properly configured the same as MySQL 5.7
(`innodb_file_per_table = 1`, `innodb_file_format = 'Barracuda'`, and
`innodb_large_prefix = 1`) since InnoDB table is created as the row
format `COMPACT` by default on MySQL 5.6, therefore indexing on string
with `utf8mb4` columns aren't succeeded.

Making `ROW_FORMAT=DYNAMIC` create table option by default for legacy
MySQL version would mitigate the indexing issue on the user side, and it
makes CI would be passed on MySQL 5.6 which is configured properly.

3 files changed, 40 insertions, 7 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6f2b49c428..07a6428196 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   MySQL: `ROW_FORMAT=DYNAMIC` create table option by default.
+
+    Since MySQL 5.7.9, the `innodb_default_row_format` option defines the default row
+    format for InnoDB tables. The default setting is `DYNAMIC`.
+    The row format is required for indexing on `varchar(255)` with `utf8mb4` columns.
+
+    *Ryuta Kamizono*
+
 *   Fix join table column quoting with SQLite.
 
     *Gannon McGibbon*
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
index 66db4e4149..47b5c4b9ec 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -77,6 +77,10 @@ module ActiveRecord
           super
         end
 
+        def create_table(table_name, options: default_row_format, **)
+          super
+        end
+
         def internal_string_options_for_primary_key
           super.tap do |options|
             if !row_format_dynamic_by_default? && CHARSETS_OF_4BYTES_MAXLEN.include?(charset)
@@ -104,6 +108,20 @@ module ActiveRecord
             end
           end
 
+          def default_row_format
+            return if row_format_dynamic_by_default?
+
+            unless defined?(@default_row_format)
+              if query_value("SELECT @@innodb_file_per_table = 1 AND @@innodb_file_format = 'Barracuda'") == 1
+                @default_row_format = "ROW_FORMAT=DYNAMIC"
+              else
+                @default_row_format = nil
+              end
+            end
+
+            @default_row_format
+          end
+
           def schema_creation
             MySQL::SchemaCreation.new(self)
           end
diff --git a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
index 261fee13eb..b14c951d03 100644
--- a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
@@ -7,6 +7,7 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   include ConnectionHelper
 
   def setup
+    ActiveRecord::Base.connection.send(:default_row_format)
     ActiveRecord::Base.connection.singleton_class.class_eval do
       alias_method :execute_without_stub, :execute
       def execute(sql, name = nil) sql end
@@ -68,18 +69,18 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
     def (ActiveRecord::Base.connection).data_source_exists?(*); false; end
 
     %w(SPATIAL FULLTEXT UNIQUE).each do |type|
-      expected = "CREATE TABLE `people` (#{type} INDEX `index_people_on_last_name`  (`last_name`))"
+      expected = /\ACREATE TABLE `people` \(#{type} INDEX `index_people_on_last_name`  \(`last_name`\)\)/
       actual = ActiveRecord::Base.connection.create_table(:people, id: false) do |t|
         t.index :last_name, type: type
       end
-      assert_equal expected, actual
+      assert_match expected, actual
     end
 
-    expected = "CREATE TABLE `people` ( INDEX `index_people_on_last_name` USING btree (`last_name`(10)))"
+    expected = /\ACREATE TABLE `people` \( INDEX `index_people_on_last_name` USING btree \(`last_name`\(10\)\)\)/
     actual = ActiveRecord::Base.connection.create_table(:people, id: false) do |t|
       t.index :last_name, length: 10, using: :btree
     end
-    assert_equal expected, actual
+    assert_match expected, actual
   end
 
   def test_index_in_bulk_change
@@ -106,7 +107,13 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_create_mysql_database_with_encoding
-    assert_equal "CREATE DATABASE `matt` DEFAULT CHARACTER SET `utf8mb4`", create_database(:matt)
+    if row_format_dynamic_by_default?
+      assert_equal "CREATE DATABASE `matt` DEFAULT CHARACTER SET `utf8mb4`", create_database(:matt)
+    else
+      error = assert_raises(RuntimeError) { create_database(:matt) }
+      expected = "Configure a supported :charset and ensure innodb_large_prefix is enabled to support indexes on varchar(255) string columns."
+      assert_equal expected, error.message
+    end
     assert_equal "CREATE DATABASE `aimonetti` DEFAULT CHARACTER SET `latin1`", create_database(:aimonetti, charset: "latin1")
     assert_equal "CREATE DATABASE `matt_aimonetti` DEFAULT COLLATE `utf8mb4_bin`", create_database(:matt_aimonetti, collation: "utf8mb4_bin")
   end
@@ -163,12 +170,12 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
       [:temp],
       returns: false
     ) do
-      expected = "CREATE TEMPORARY TABLE `temp` ( INDEX `index_temp_on_zip`  (`zip`)) AS SELECT id, name, zip FROM a_really_complicated_query"
+      expected = /\ACREATE TEMPORARY TABLE `temp` \( INDEX `index_temp_on_zip`  \(`zip`\)\)(?: ROW_FORMAT=DYNAMIC)? AS SELECT id, name, zip FROM a_really_complicated_query/
       actual = ActiveRecord::Base.connection.create_table(:temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query") do |t|
         t.index :zip
       end
 
-      assert_equal expected, actual
+      assert_match expected, actual
     end
   end