# Conversion to utf8mb4 and replication

**URL:** <https://forums.percona.com/t/conversion-to-utf8mb4-and-replication/3624>\
**Category:** Other MySQL® Questions\
**Created:** [July 18, 2014, 2:14am UTC](https://forums.percona.com/t/conversion-to-utf8mb4-and-replication/3624 "2014-07-18T02:14:31Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![juris](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/juris/32/1024_2.png) [@juris](https://forums.percona.com/u/juris)\
**Post date:** [July 18, 2014, 2:14am UTC](https://forums.percona.com/t/conversion-to-utf8mb4-and-replication/3624/1 "2014-07-18T02:14:31Z")

</div>

Hi all,

I’ve got a very strange problem here.

So, there is a database which contains a single table called “questions”:

```auto
+-----------------------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------------+---------------+------+-----+---------+-------+
| id | bigint(11) | NO | PRI | NULL | |
| question_text | varchar(300) | NO | | NULL | |
+-----------------------+---------------+------+-----+---------+-------+

```

I am trying to convert it from standard utf8 to utf8mb4. In order to reduce downtime, I am trying to do it in the following way: [LIST=1]  
[_]Create replica using innobackupex  
[_]Stop replication  
[\*]Launch pt-online-schema-change on a slave:

```auto
pt-online-schema-change --nodrop-old-table --nodrop-new-table --execute --alter "CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci" "D=questions,t=questions"

```

[_]Start replication and wait till it catches the master  
[_]Set master as read-only  
[\*]Stop replication and promote slave to be a new master  
[/LIST] Everything works perfectly till the 4th step. If I run “start slave” after pt-online-schema-change, replication fails with the following error:

```auto
.questions' cannot be converted from type 'varchar(900)' to type 'varchar(300)', Error_code: 1677
140717 15:24:41 [ERROR] Error running query, slave SQL thread aborted. Fix the problem, and restart the slave SQL thread with "SLAVE START". We stopped at log 'mysql-bin.004315' position 28070522

```

Percona MySQL Server version: 5.5.16

Any ideas why is it failing after conversion to utf8mb4?