sqlalchemy impl calls back to DB API

[Chris Behrens]

In 3 places, sqlalchemy has calls back to the DB API:

db.instance_get_by_uuid(context, instance_uuid)
db.aggregate_get(context, aggregate_id)
db.ec2_instance_create(context, instance_ref['uuid'])

While this an eventlet bug, when tpool is enabled.. The call path ends up being:

tpool.execute { sqlalchemy_method { tpool.execute{ sqlalchemy_method } } }

eventlet tries to deal with recursive tpool.execute()s but it seems to cause lockups.

Either way, it's not necessary to call back to DB API from the sqlalchemy backend, and I think that should be avoided.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/24372

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/24372
Committed: http://github.com/openstack/nova/commit/cef34cd69156036c855ec217225edfce65b63d3c
Submitter: Jenkins
Branch: master

commit cef34cd69156036c855ec217225edfce65b63d3c
Author: Chris Behrens <email address hidden>
Date: Wed Mar 13 21:41:43 2013 +0000

    Remove sqlalchemy calling back to DB API

    sqlalchemy unnecessarily calls back to DB API in a few spots. It's
    more efficient to not do so.

    Also, when dbapi_use_tpool is enabled, this causes a lock up due to an
    eventlet bug.

    Fixes bug 1154811

    Change-Id: I5937a2dce85a09502f40ebcd99afb441938c1289