mysql or mariadb - how does diesel choose when both available

[tessus]

Backend

MySQL

Diesel version

2.3.3

Diesel Features

"chrono", "r2d2", "numeric"

Operating System Version

Fedora 42 and 43

Third party libraries

No response

What do you want to do?

During the issue dani-garcia/vaultwarden#6416 mariadb and mysql came up.
I just wanted to ask what happens, if one has both clients installed (when compiling mysql diesel): the mysql client and the mariadb connector. How does diesel choose? Is there a flag or is mysql the 1st order of preference?

I could of course test it, but then I still wouldn't know whether the picked library was picked on purpose or by chance.

Compile time error

No response

What code do you already have?

No response

Additional details

No response

Checklist

• I have already looked over the issue tracker and the discussion forum for similar possible closed issues.

[weiznich]

It's complicated and likely depends a lot on your system configuration.

mysqlclient-sys will first look for libmysqlclient, then for libmariadb. As it links stuff dynamically by default you still can end up with the application using the other lib at runtime. That will likely cause other interesting issues as well as these libraries are also not abi compatible in other places as well.

Relevant source code: https://github.com/sgrif/mysqlclient-sys/blob/master/build.rs#L57-L58

Edit: the mysqlclient-sys also allows to configure which lib to link via environment variables. See the Readme there for details

[tessus]

Thanks for the reply.

mysqlclient-sys will first look for libmysqlclient, then for libmariadb.

In that case all should be good.

As it links stuff dynamically by default you still can end up with the application using the other lib at runtime.

No, I do not believe so. According to the code you referenced the first one found is picked for linking.

The mysql and mariadb libs are named differently:

/usr/lib64/mysql/libmysqlclient.so.24 vs /usr/lib64/libmariadb.so.3

So in case diesel is linked with mysql, it is impossible that the mariadb library is used at runtime.
The only time this will happen is between the libraries from the mysql oracle package and fedora package, which is perfectly fine, since they are ABI compatible.

[weiznich]

In that case all should be good.

As long as pkg-config is configured for both packages.

So in case diesel is linked with mysql, it is impossible that the mariadb library is used at runtime.
The only time this will happen is between the libraries from the mysql oracle package and fedora package, which is perfectly fine, since they are ABI compatible.

As long as these libraries have different names that's true. The problem there is that some distributions provide packages which add sym links to make libmariadb available as libmysqlclient as well. That would then be problematic.

---

Anyway hopefully #4866 should fix the whole underlying problem soon.

[tessus]

The problem there is that some distributions provide packages which add sym links to make libmariadb available as libmysqlclient as well. That would then be problematic.

I agree with you. This would be a problem. A serious one at that.

Distros should not be doing this, but I understand why they would, if only mariadb is installed. Personally I still think this is a mistake, but there's nothing I can do about it. On the other side, it would probably not be an issue, if both libaries were installed.
This is certainly a nightmare for packagers, who create a single package for multiple distros.
Luckily for me, I do not fall into this category.

But yes, caution is advised either way. ;-)