Repair multiple engines

[Renat Akhmerov]

We now can't use multiple engines if we run workflows containing joins. We need to fix it.

[Renat Akhmerov (rakhmerov)]

We need to find a solution how to avoid or handle database (i.e. MySQL) deadlocks properly. We also have users using postgreSQL.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/413416

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/413416
Committed: https://git.openstack.org/cgit/openstack/mistral/commit/?id=62862ca0b72ca0b91a2b6e598ea55fec084f57d8
Submitter: Jenkins
Branch: master

commit 62862ca0b72ca0b91a2b6e598ea55fec084f57d8
Author: Renat Akhmerov <email address hidden>
Date: Wed Dec 21 12:30:34 2016 +0700

    Refresh object state after lock acquisition in WithItemsTask

    * We need to refresh task state once we acquired the 'with-items'
      lock to prevent modifying stale values cached by SQLAlchemy
      session. For this purpose, new DB API method refresh() was
      added. Without this change 'with-items' task doesn't work
      properly in case of using multiple engines.

    Change-Id: Id5a1d2cf03090279e6df3805562e00d300b89953
    Closes-Bug: #1640378
    Partial-Bug: #1640379

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/415618
Committed: https://git.openstack.org/cgit/openstack/mistral/commit/?id=4a86e9665a5bce77ad72944c49483047002cae4f
Submitter: Jenkins
Branch: master

commit 4a86e9665a5bce77ad72944c49483047002cae4f
Author: Renat Akhmerov <email address hidden>
Date: Thu Dec 29 13:57:04 2016 +0700

    Add 'retry_on_deadlock' decorator

    * 'retry_on_deadlock' decorator allows to retry a method if a DB
      deadlock occurs as a result of some DB operation. Deadlocks
      occur sometimes when we use named locks, at least when using
      MySQL as a DB backend.
    * Minor cosmetic changes

    Partial-Bug: #1640379

    Change-Id: I4fb342a3314e4d23a1f787e2cb6f1d70196663c8

[Renat Akhmerov (rakhmerov)]

Essentially, it's fixed but more testing is needed.