During the development of the myloader innodb-optimize-keys option, which was released in version 0.10.7, we found several issues and opportunities to improve the process. We had to change the approach, reimplement some of the core functionality and add a couple of data structures. That allowed us to implement, at a really low cost, a feature [&]

https://www.percona.com/blog/myloader-stops-causing-data-fragmentation/