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Excerpts from Adam Young's message of 2013-07-08 13:18:55 -0700:
> On 07/01/2013 01:35 PM, Clint Byrum wrote:
> > The way the new keystone-manage command "token_flush" works right now
> > is quite broken by MySQL and InnoDB's gap locking behavior:
> >
> > https://bugs.launchpad.net/1188378
> >
> > Presumably other SQL databases like PostgreSQL will have similar problems
> > with doing massive deletes, but I am less familiar with them.
> >
> > I am trying to solve this in keystone, and my first attempt is here:
> >
> > https://review.openstack.org/#/c/32044/
> >
> > However, MySQL does not support using "LIMIT" in a sub-query that
> > is feeding an IN() clause, so that approach will not work. Likewise,
> > sqlalchemy does not support the MySQL specific extension to DELETE which
> > allows it to have a LIMIT clause.
> >
> > Now, I can do some hacky things, like just deleting all of the expired
> > tokens from the oldest single second, but that could also potentially
> > be millions of tokens, and thus, millions of gaps to lock.
> >
> > So, there is just not one way to work for all databases, and we have to
> > have a special mode for MySQL.
> >
> > I was wondering if anybody has suggestions and/or examples of how to do
> > that with sqlalchemy.
> >
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> In general, if you have millions of roles, you need a real database.  I 
> would not try to work through SQL Alchemy for this. Instead, you 
> probably just want to make sure that the token_flush is run fairly 
> regularly on your database.
> 

I'm not sure I understand you.

* I am asking about millions of tokens, not roles.
* I am asking about MySQL.. presumably a "real" database.
* In the bug, I am suggesting that running token_flush once every
  second will be _a disaster_ on a busy site with MySQL because of
  the gap locking behavior in InnoDB. We need to delete a small number
  per transaction.