1 files changed, 24 insertions, 10 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 88fff83a9e..09242a0f14 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -43,9 +43,11 @@ module ActiveRecord
       }
 
       class StatementPool < ConnectionAdapters::StatementPool # :nodoc:
-        private def dealloc(stmt)
-          stmt.close
-        end
+        private
+
+          def dealloc(stmt)
+            stmt.close
+          end
       end
 
       def initialize(connection, logger, connection_options, config)
@@ -53,8 +55,8 @@ module ActiveRecord
 
         @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
 
-        if version < "5.1.10"
-          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.1.10."
+        if version < "5.5.8"
+          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.5.8."
         end
       end
 
@@ -114,6 +116,14 @@ module ActiveRecord
         true
       end
 
+      def supports_longer_index_key_prefix?
+        if mariadb?
+          version >= "10.2.2"
+        else
+          version >= "5.7.9"
+        end
+      end
+
       def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
         query_value("SELECT GET_LOCK(#{quote(lock_name.to_s)}, #{timeout})") == 1
       end
@@ -127,7 +137,7 @@ module ActiveRecord
       end
 
       def index_algorithms
-        { default: "ALGORITHM = DEFAULT".dup, copy: "ALGORITHM = COPY".dup, inplace: "ALGORITHM = INPLACE".dup }
+        { default: +"ALGORITHM = DEFAULT", copy: +"ALGORITHM = COPY", inplace: +"ALGORITHM = INPLACE" }
       end
 
       # HELPER METHODS ===========================================
@@ -241,7 +251,7 @@ module ActiveRecord
       end
 
       # Create a new MySQL database with optional <tt>:charset</tt> and <tt>:collation</tt>.
-      # Charset defaults to utf8.
+      # Charset defaults to utf8mb4.
       #
       # Example:
       #   create_database 'charset_test', charset: 'latin1', collation: 'latin1_bin'
@@ -250,8 +260,12 @@ module ActiveRecord
       def create_database(name, options = {})
         if options[:collation]
           execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT COLLATE #{quote_table_name(options[:collation])}"
+        elsif options[:charset]
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET #{quote_table_name(options[:charset])}"
+        elsif supports_longer_index_key_prefix?
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET `utf8mb4`"
         else
-          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET #{quote_table_name(options[:charset] || 'utf8')}"
+          raise "Configure a supported :charset and ensure innodb_large_prefix is enabled to support indexes on varchar(255) string columns."
         end
       end
 
@@ -378,7 +392,7 @@ module ActiveRecord
 
       def add_index(table_name, column_name, options = {}) #:nodoc:
         index_name, index_type, index_columns, _, index_algorithm, index_using, comment = add_index_options(table_name, column_name, options)
-        sql = "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}".dup
+        sql = +"CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}"
         execute add_sql_comment!(sql, comment)
       end
 
@@ -771,7 +785,7 @@ module ActiveRecord
           # https://dev.mysql.com/doc/refman/5.7/en/set-names.html
           # (trailing comma because variable_assignments will always have content)
           if @config[:encoding]
-            encoding = "NAMES #{@config[:encoding]}".dup
+            encoding = +"NAMES #{@config[:encoding]}"
             encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
             encoding << ", "
           end