Nova is having a related issue, where we are hitting issues in our unit
tests.

https://bugs.launchpad.net/nova/+bug/1328997

Stderr: 'ERROR: database "openstack_citest" is being accessed by other
users\\nDETAIL: There are 1 other session(s) using the database.\\n\''

http://logs.openstack.org/76/98376/1/gate/gate-nova-python27/d2a0593/console.html



On Mon, Jun 9, 2014 at 4:18 PM, Devananda van der Veen <
devananda....@gmail.com> wrote:

> Mike,
>
> For the "typical" case, your proposal sounds reasonable to me. That
> should protect against cross-session locking while still getting the
> benefits of testing DML without committing to disk.
>
> The issue I was originally raising is, of course, the "special" case
> -- testing of migrations -- which, I think, could be solved in much
> the same way. Given N test runners, create N empty schemata, hand each
> migration-test-runner a schema from that pool. When that test runner
> is done, drop and recreate that schema.
>
> AIUI, Nodepool is already doing something similar here:
>
> https://git.openstack.org/cgit/openstack-infra/nodepool/tree/nodepool/tests/__init__.py#n71
>
> Regards,
> Devananda
>
>
>
> On Mon, Jun 9, 2014 at 12:58 PM, Mike Bayer <mba...@redhat.com> wrote:
> >
> > On Jun 9, 2014, at 1:08 PM, Mike Bayer <mba...@redhat.com> wrote:
> >
> >>
> >> On Jun 9, 2014, at 12:50 PM, Devananda van der Veen <
> devananda....@gmail.com> wrote:
> >>
> >>> There may be some problems with MySQL when testing parallel writes in
> >>> different non-committing transactions, even in READ COMMITTED mode,
> >>> due to InnoDB locking, if the queries use non-unique secondary indexes
> >>> for UPDATE or SELECT..FOR UPDATE queries. This is done by the
> >>> "with_lockmode('update')" SQLAlchemy phrase, and is used in ~10 places
> >>> in Nova. So I would not recommend this approach, even though, in
> >>> principle, I agree it would be a much more efficient way of testing
> >>> database reads/writes.
> >>>
> >>> More details here:
> >>> http://dev.mysql.com/doc/refman/5.5/en/innodb-locks-set.html and
> >>> http://dev.mysql.com/doc/refman/5.5/en/innodb-record-level-locks.html
> >>
> >> OK, but just to clarify my understanding, what is the approach to
> testing writes in parallel right now, are we doing CREATE DATABASE for two
> entirely distinct databases with some kind of generated name for each one?
>  Otherwise, if the parallel tests are against the same database, this issue
> exists regardless (unless autocommit mode is used, is FOR UPDATE accepted
> under those conditions?)
> >
> > Took a look and this seems to be the case, from oslo.db:
> >
> >         def create_database(engine):
> >             """Provide temporary user and database for each particular
> test."""
> >             driver = engine.name
> >
> >             auth = {
> >                 'database': ''.join(random.choice(string.ascii_lowercase)
> >                                     for i in moves.range(10)),
> >                 # ...
> >
> >             sqls = [
> >                 "drop database if exists %(database)s;",
> >                 "create database %(database)s;"
> >             ]
> >
> > Just thinking out loud here, I’ll move these ideas to a new wiki page
> after this post.    My idea now is that OK, we provide ad-hoc databases for
> tests, but look into the idea that we create N ad-hoc databases,
> corresponding to parallel test runs - e.g. if we are running five tests
> concurrently, we make five databases.   Tests that use a database will be
> dished out among this pool of available schemas.   In the *typical* case
> (which means not the case that we’re testing actual migrations, that’s a
> special case) we build up the schema on each database via migrations or
> even create_all() just once, run tests within rolled-back transactions
> one-per-database, then the DBs are torn down when the suite is finished.
> >
> > Sorry for the thread hijack.
> >
> >
> >
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev@lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>
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