Comment 5 for bug 1853071

I have some more updates/clues:

There appears to be a lot of queries causing the blocking that show a NULL SQL query. It seems these are actually "rollback" operations.

As you can see there are 2 blocked transactions, each waiting on another transaction. If you view these transactions, or view the processlist, you will see it reports a NULL query: http://paste.openstack.org/show/786464/

We can use the event_transaction_history and _current tables in performance_schema to show actual SQL history for these blocking transactions. Many appear to be rollbacks from other agent timestamp update operations themselves. Others are sometimes different transactions altogether. We can see many threads currently trying to perform operations too, with majority being ROLLBACK:

http://paste.openstack.org/show/786465/