Comment 12 for bug 1328997

Reviewed: https://review.openstack.org/99608
Committed: https://git.openstack.org/cgit/openstack/oslo.db/commit/?id=314496a5815f9e946f1ec87e6e6610c44bfc07bd
Submitter: Jenkins
Branch: master

commit 314496a5815f9e946f1ec87e6e6610c44bfc07bd
Author: Roman Podoliaka <email address hidden>
Date: Thu Jun 12 12:22:49 2014 +0300

    Prevent races in opportunistic db test cases

    Opportunistic db test cases create schemas on demand, so that each
    test case which inherits the base test case class, will get its own
    db schema (i. e. races between tests are not possible).

    In order to do schema provisioning we have to connect to RDBMS server
    first. So far we've been connecting to the openstack_citest database,
    which is guaranteed to exist on CI nodes. It turns out, there are a
    few test cases in Nova (maybe in other projects as well), that drop
    and recreate the openstack_citest database. If they happen to do that
    when the opportunistic db fixture is in the middle of provisioning a
    schema, those tests will fail (as there is an an open session to the
    database and thus it can't be dropped).

    This can be solved easily by changing the way we provision new
    schemas in opportunistic db test cases as actually, we don't have to
    connect to the openstack_citest database at all:

     - for MySQL we can use an empty db name to connect to MySQL server,
       but not to a particular database
     - PostgreSQL requires us to specify the database name. We can use
       the service postgres database here (PostgreSQL shell utils such
       as createdb, createuser, etc use it for the very same reason)

    Closes-Bug: #1328997

    Change-Id: I0dc0becc5cb40d3dab3289c865a96113522a0b9a