We've ported "filesort with small limit" optimization from mysql-5.6 into MariaDB 10.0.
The problem is, it is impossible to see whether that optimization is used or not.
In MySQL, one can check this as follows
- set optimizer_trace=1
- SELECT // need to run SELECT, not EXPLAIN
- select * from optimizer_trace
And then look for something like this:
In MariaDB, there is no optimizer_trace, so one can't see it at all.