[openstack-dev] [Neutron] Issue with pymysql

Mike Bayer mbayer at redhat.com
Fri Jun 12 15:37:45 UTC 2015

On 6/11/15 9:32 PM, Eugene Nikanorov wrote:
> Hi neutrons,
> I'd like to draw your attention to an issue discovered by rally gate job:
> http://logs.openstack.org/96/190796/4/check/gate-rally-dsvm-neutron-rally/7a18e43/logs/screen-q-svc.txt.gz?level=TRACE
> I don't have bandwidth to take a deep look at it, but first impression 
> is that it is some issue with nested transaction support either on 
> sqlalchemy or pymysql side.
> Also, besides errors with nested transactions, there are a lot of Lock 
> wait timeouts.
> I think it makes sense to start with reverting the patch that moves to 
> pymysql.
My immediate reaction is that this is perhaps a concurrency-related 
issue; because PyMySQL is pure python and allows for full blown eventlet 
monkeypatching, I wonder if somehow the same PyMySQL connection is being 
used in multiple contexts.  E.g. one greenlet starts up a savepoint, 
using identifier "_3" which is based on a counter that is local to the 
SQLAlchemy Connection, but then another greenlet shares that PyMySQL 
connection somehow with another SQLAlchemy Connection that uses the same 

I'm not saying this is a bug in PyMySQL or Eventlet necessarily, it 
could be a bug in Neutron itself, since none of this code has ever been 
used with a true context-switching greenlet environment at the database 
connection level.

> Thanks,
> Eugene.
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