Yona's default DB encoding type is 'UTF8MB4' which make enable
to use large byte for external characters, like emoji.
It has little bit performance loss but mostly works good.
But there exist other side effect.
Index column uses more space, too.
If db file format is 'antelope' which default db file format
for MariaDB/MySQL, following error can be occurred.
```
Specified key was too long; max key length is 767 bytes [ERROR:1071, SQLSTATE:42000]
```
To avoid it, change file type and use large prefix.
```
set global innodb_file_format = BARRACUDA;
set global innodb_large_prefix = ON;
```
Don't worry about change DB file format to 'BARRACUDA'.
In the most of cases 'BARRACUDA' is better, if you don't use clustering.
You can see addition info about 767byte error at
http://mechanics.flite.com/blog/2014/07/29/using-innodb-large-prefix-to-avoid-error-1071/