I don’t think it’ll surprise anybody if I say that MariaDB or MySQL server knows a lot more about server system variables, then just their values. Indeed, every variable can be session or global only, read-only or writable, it has an associated help text (that is printed on
mysqld --help --verbose), certain variables only accept values from a given set of strings (this set of allowed values is also printed in
mysqld --help --verbose since MariaDB 10.1.0), numeric variables have lower and upper range boundaries of valid values (that are never printed anywhere), and so on. I always thought it’s kind of a waste that there is no way to query this information. That could’ve been very convenient, in particular for various GUI clients — they could show the help in tooltips, validate values and so on.
But recently[Read more...]