I used tmpfs to mount a dir on my system (a 10GB RAM dir) and passed
this to tmpdir in my.cnf. My idea was to try to speed up index
creation, because it is taking hours. However, it did not work.

The tmpfs dir is completely idle during the index creation even though
mysql states "copy to tmp table".

What is it wrong?

I want MySQL create temporary tables in memory rather than create them
on disk.

Thanks,