Documenting optimizing MySQL for performance

Hi,

this may be interesting for people who are experiencing slow execution times of their migration and maybe it could be worth including it in the documentation.

During the last few days I've worked on migrating about 200k users from a Drupal 6 DB (using the MyISAM storage engine) to a Drupal 7 DB (InnoDB). I've set up a 'large' Amazon Web Service instance and configured it especially for this migration (yes, I took care to meet the needs of both MyISAM and InnoDB). Although I've spend several hours on tweaking the environment variables, I wasn't able to increase the throughput beyond an average of 100 users per minute. Even this value had to be bought with setting 'innodb_flush_log_at_trx_commit' to '0'. But once I set the storage engine of all D7 tables from InnoDB to MyISAM, the throughput was increased to about 1000 users/minute. I've set the storage engine of the D7 DB back to InnoDB after the migration and the site's working fine.