Comment 1 for bug 1009546

I remember we had this problem too. Don't know if you already have ideas on why this happens and how to solve this, however we ended up ensuring we ran db sync on a single host and that each nova upstart script would check that the db was at the right version before starting the service (and failing do to so otherwise).

We did this to get rid of the contention altogether; unless you ensure that nova-manage db sync locks out the entire DB (or tables affected) during the migration process, I cannot see any other way to solve the issue.

Hope this help.