Comment 12 for bug 1182481

Update:

Now that our environment has grown. Simply deleting the expired tokens is not helping. I have found a temporary work around and that was to revert from PKI tokens to UUID based tokens.

The mySQL usage has droped from 110% to 10-15% and it is very quick now. If you are interested in making this change it is very simple. Edit your keystone.conf file and set the following:
 token_format = UUID

Restart the keystone service and you are good to go.

This is just temporary as I am sure we would all like the added benefits of PKI.

Here are some interesting ideas that may be worth checking out:

http://blog.gridcentric.com/bid/318277/Boosting-OpenStack-s-Parallel-Performance I have not had the time to test them but plan to soon and will update this bug.

Thanks,
Adam