Open Stack

Just wanted to put this out there to hopefully spread awareness and
prevent it from happening more.

We had a bug reported in Cinder of hitting a deadlock when attempting
to deelte multiple volumes simultaneously:

https://bugs.launchpad.net/cinder/+bug/1685818

Some were seeing it, but others were not able to reproduce the error
in their environments.

What it came down to is the use of "mysql://" vs "mysql+pymysql://"
for the database connection string. Big thanks to Gerhard Muntingh
for noticing this difference.

Basically, when using "mysql://" for the connection string, that uses
blocking calls that prevent other "threads" from running at the same
time, causing these deadlocks.

This doesn't just impact Cinder, so I wanted to get the word out that
it may be worth checking your configurations and make sure you are
using "mysql+pymysql://" for your connections.

Sean