[openstack-dev] [Keystone] Best way to do something MySQL-specific?

Sean Dague sean at dague.net
Mon Jul 8 21:18:02 UTC 2013

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.

Honestly, my answer is typically to ask Jay, he understands a lot of the 
ways to get SQLA to do the right thing in mysql.


Sean Dague

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