Re: MySQL 5.5 vs 5.6 character set issue

[Rick James]

You have raised several issues.

* Defaults changing. Well, that does happen. Protect yourself by explicitly specifying things -- CHARACTER SET latin1 (or utf8, etc) can be put on CREATE DATABASE, CREATE TABLE, and/or a column in a table.

* For practical reasons, there is a limit on the size of an each index. If you need a non-UNIQUE index, use a 'prefix', eg: INDEX vchar_col(50). (There are pros and cons of taking that approach.) If you need a UNIQUE index, that is, you desire a uniqueness constraint, you could either do it in your code, or have another column with the MD5 of that varchar. Then have a UNIQUE index on that column. (Again, there are pros and cons.)

* Performance of wide indexes -- well, that is essentially why the limits exist.

* "multibyte" -- latin1: 1 byte per character; utf8: up to 3 bytes per character ("3" is used in certain situations, such as index creation, to provide an upper bound); utf8mb4: up to 4 bytes per character (this charset was added to account for some newer Chinese characters).

* "large key" parameter -- I would look for other solutions (as mentioned above) first. Would you care to elaborate on the field's purpose and whether the index needs to be UNIQUE?