Hello all,

As some folks may know the OSIC cloud1 just upgraded to Mitaka last
week (I know what's old is new again, sorry). Since the upgrade things
have been running fairly smoothly however there's been one issue that
has left me scratching my head. When attempting a scale out test we've
run into issues where the nova client was returning a message
indicating it had encountered a DB deadlock [0]. In attempting to gain
more information we enabled debug logging and collected the following
[1] (Here is a pretty version for the tracebacks [4]). This is the
command we're using to build all of the VMs [2] which was being used
to build 3 vms per compute node for 242 compute nodes. Once the
instances are all online we grab the nodes IPv6 address and ensure
we're able to SSH to them. While we're happy to report that almost all
of the VMs came online in one shot we did run into a few of these DB
dead lock messages and would like to see if folks out on the interwebs
have seen or experienced such problems. If so we'd love to know if
there's some remediation that we can use to make this all even
happier. It should be noted that this is not a Major issue at this
point, 3 out of 726 VMs didn't come online due to the problem but it
would be amazing if there was something we could do to generally
resolve this.

Other potentially interesting things:
  * DB is MariaDB "mariadb-galera-server-10.0". The replication system
is using xtrabackup from percona with version "2.3.5-1.trusty".
  * The DB is a 3 node cluster however the connection to the cluster
is using a VIP on our loadbalancer and the services are only ever
connected to 1 of the three nodes; this is for both reads and writes.
Should a node become un-happy the load balancer promotes and demotes
always ensuring only 1 node is being connected to.
  * While reproducing this issue repeatedly we've watched wsrep to see
if nodes we're dropping or otherwise having a bad day. To our dismay
there were no un-happy nodes and the wsrep state seemed to remain
OPERATIONAL with minimal latency (Example [3]).
  * For all of the OpenStack Services we use pymsql as it's DB driver
we were using mysql-python but I believe OpenStack-Ansible switched in
kilo due to DB deadlock issues we were experiencing.
  * Cloud1 is running nova at commit
"dd30603f91e6fd3d1a4db452f20a51ba8820e1f4" which was the HEAD of
"stable/mitaka" on 29-09-2016. This code is in production today with
absolutely no modifications.

Any insight would be greatly appreciated. Thanks again everyone!

[0] http://paste.openstack.org/show/586302/
[1] http://paste.openstack.org/show/586309/
[2] http://paste.openstack.org/show/586298/
[3] http://paste.openstack.org/show/586306/
[4] http://paste.openstack.org/show/586307/

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