[debian-mysql] Bug#813413: Upgrade from mysql-server-5.5 can break configurations that use the conf.d directory

[Justin Pasher]

It's understandablehow this could be desirable in different use cases. 
My concern is that this could catch quite a few people with an 
unexpected config change. In my case, the problem was very obvious, as 
remote connection no longer worked. However, it's possible that some 
people might be using it to override common MySQL settings on a 
per-server basis (such as settings related to memory usage, temp table 
sizes, buffer sizes, etc). In those cases, the server would probably 
continue running as if nothing was wrong, but they could experience a 
sudden performance hit when the daemon is suddenly not utilizing as much 
memory for caching and the like.

Just to confirm, the implied behavior in MySQL 5.5 was that options set 
within conf.d/ would override the global defaults under 
/etc/mysql/my.cnf (since the conf.d/ directory was included at the end 
of my.cnf). Now the default behavior in MySQL 5.6 is that the global 
config file (now in /etc/mysql/mysql.conf.d/mysqld.cnf) overrides the 
settings withing conf.d/ files. This is the main gotcha that concerned 
me, since it wasn't something I was expecting. I didn't really see 
anything in the Debian changelog that would warn of this, aside from 
"Switch to new /etc/mysql/my.cnf management scheme" for 5.6.25-2.

As far as a way to solve it for both needs, I'm not sure what would be 
the best way. It does seem like the upgrade from 5.5 to 5.6 would be the 
best time to hammer it out though, since someone will be consciously 
performing this upgrade. Maybe it's better to move any existing custom 
files under conf.d/ into the mysql.conf.d/ directory (is that even 
tracked)? They could be named in a way to ensure they are included after 
the other mysql*.cnf files. I'm not familiar with all of the upgrade 
paths people might be following (for me it was just a "routine" MySQL 
server upgrade), so I don't know how feasible this is. I would think at 
least at a minimum some sort of warning that this is happening so it 
wouldn't catch people completely off-guard.

Thanks.

Justin Pasher