[#MDEV-17662] Default to UTF8

It has both good and bad sides. Good that users who need non-latin1 characters won't longer need to change the default character set. Bad for latin1-only users, because it comes with an unknown slowdown (~~MDEV-20416~~) and because it'll truncate indexes. Compare:

MariaDB [test]> create table t1 (a varchar(2000), index(a)) character set utf8mb4;

Query OK, 0 rows affected, 1 warning (0.013 sec)

Warning (Code 1071): Specified key was too long; max key length is 1000 bytes

MariaDB [test]> show create table t1;

+-------+-----------------------------------------------------------------------------------------------------------------+

| Table | Create Table                                                                                                    |

+-------+-----------------------------------------------------------------------------------------------------------------+

| t1    | CREATE TABLE `t1` (

  `a` varchar(2000) DEFAULT NULL,

  KEY `a` (`a`(250))

) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 |

+-------+-----------------------------------------------------------------------------------------------------------------+

MariaDB [test]> create table t2 (a varchar(2000), index(a));

Query OK, 0 rows affected, 1 warning (0.017 sec)

Warning (Code 1071): Specified key was too long; max key length is 1000 bytes

MariaDB [test]> show create table t2;

+-------+--------------------------------------------------------------------------------------------------------------------+

| Table | Create Table                                                                                                       |

+-------+--------------------------------------------------------------------------------------------------------------------+

| t2    | CREATE TABLE `t2` (

  `a` varchar(2000) DEFAULT NULL,

  KEY `a` (`a`(1000))

) ENGINE=MyISAM DEFAULT CHARSET=latin1 |

+-------+--------------------------------------------------------------------------------------------------------------------+

For UNIQUE keys it's even worse, a UNIQUE cannot be automatically truncated, so it'll be converted to a HASH based constraint, and such a constraint isn't yet supported by the optimizer (MDEV-17081). So, while a UNIQUE will still work (it's a new 10.4 feature, in 10.3 it'd be an error), it won't longer be used as an index unless MDEV-17081 is closed.

[MDEV-17662] Default to UTF8 Created: 2018-11-10 Updated: 2021-11-04 Resolved: 2021-04-06
Status:	Closed
Project:	MariaDB Server
Component/s:	Character Sets
Fix Version/s:	N/A

[MDEV-17662] Default to UTF8 Created: 2018-11-10 Updated: 2021-11-04 Resolved: 2021-04-06