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What is in the variable named 'query' that you are trying to merge into the
session? Can you include the full create_port_postcommit method? The line
raising the exception ends with "{'port_id': port_id})" and that doesn't
matching anything included in your sample.


On Wed, Jun 25, 2014 at 6:53 PM, Li Ma <skywalker.nick at gmail.com> wrote:

> Here's a code sample which can raise db lock wait exception:
>
> def create_port_postcommit(self, context):
>
> port_id = ...
> with session.begin(subtransactions=True):
>     try:
>         binding = (session.query(models.PortBinding).
>                   filter(models.PortBinding.port_id.startswith(port_id)).
>                   one())
>         # Here I modify some attributes if port binding is existed
>         session.merge(query)
>     except exc.NoResultFound:
>         # Here I insert new port binding record to initialize some
> attributes
>     except ...
>         LOG.error("error happened")
>
> The exception is as follows:
> 2014-06-25 10:05:17.195 9915 ERROR neutron.plugins.ml2.managers
> [req-961680da-ce69-43c6-974c-57132def411d None] Mechanism driver 'hello'
> failed in create_port_postcommit
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers Traceback
> (most recent call last):
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers   File
> "/usr/lib/python2.6/site-packages/neutron/plugins/ml2/managers.py", line
> 158, in _call_on_drivers
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers
> getattr(driver.obj, method_name)(context)
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers   File
> "/usr/lib/python2.6/site-packages/neutron/plugins/ml2/drivers/mech_hello.py",
> line 95, in create_port_postcommit
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers
> {'port_id': port_id})
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers   File
> "/usr/lib64/python2.6/site-packages/SQLAlchemy-0.7.8-py2.6-linux-x86_64.egg/sqlalchemy/orm/session.py",
> line 402, in __exit__
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers
> self.commit()
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers   File
> "/usr/lib64/python2.6/site-packages/SQLAlchemy-0.7.8-py2.6-linux-x86_64.egg/sqlalchemy/orm/session.py",
> line 314, in commit
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers
> self._prepare_impl()
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers   File
> "/usr/lib64/python2.6/site-packages/SQLAlchemy-0.7.8-py2.6-linux-x86_64.egg/sqlalchemy/orm/session.py",
> line 298, in _prepare_impl
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers
> self.session.flush()
>
> ...
>
> 2014-06-25 10:05:17.195 9915 TRACE neutron.plugins.ml2.managers
> OperationalError: (OperationalError) (1205, 'Lock wait timeout exceeded;
> try restarting transaction') 'INSERT INTO ml2_port_bindings (port_id, host,
> vnic_type, profile, vif_type, vif_details, driver, segment) VALUES (%s, %s,
> %s, %s, %s, %s, %s, %s)' (...)
>
> It seems that the transaction in the postcommit cannot be committed.
>
> Thanks a lot,
> Li Ma
>
> ----- Original Message -----
> From: "Li Ma" <skywalker.nick at gmail.com>
> To: "OpenStack Development Mailing List (not for usage questions)" <
> openstack-dev at lists.openstack.org>
> Sent: 星期三, 2014年 6 月 25日 下午 6:21:10
> Subject: Re: [openstack-dev] [Neutron ML2] Potential DB lock when
> developing new mechanism driver
>
> Hi Kevin,
>
> Thanks for your reply. Actually, it is not that straightforward.
> Even if postcommit is outside the 'with' statement, the transaction is not
> 'truly' committed immediately. Because when I put my db code (reading and
> writing ml2-related tables) in postcommit, db lock wait exception is still
> thrown.
>
> Li Ma
>
> ----- Original Message -----
> From: "Kevin Benton" <blak111 at gmail.com>
> To: "OpenStack Development Mailing List (not for usage questions)" <
> openstack-dev at lists.openstack.org>
> Sent: 星期三, 2014年 6 月 25日 下午 4:59:26
> Subject: Re: [openstack-dev] [Neutron ML2] Potential DB lock when
> developing new mechanism driver
>
>
>
> The post_commit methods occur outside of the transactions. You should be
> able to perform the necessary database calls there.
>
>
> If you look at the code snippet in the email you provided, you can see
> that the 'try' block surrounding the postcommit method is at the same
> indentation-level as the 'with' statement for the transaction so it will be
> closed at that point.
>
>
> Cheers,
> Kevin Benton
>
>
> --
> Kevin Benton
>
>
>
> On Tue, Jun 24, 2014 at 8:33 PM, Li Ma < skywalker.nick at gmail.com > wrote:
>
>
> Hi all,
>
> I'm developing a new mechanism driver. I'd like to access ml2-related
> tables in create_port_precommit and create_port_postcommit. However I find
> it hard to do that because the two functions are both inside an existed
> database transaction defined in create_port function of ml2/plugin.py.
>
> The related code is as follows:
>
> def create_port(self, context, port):
> ...
> session = context.session
> with session.begin(subtransactions=True):
> ...
> self.mechanism_manager.create_port_precommit(mech_context)
> try:
> self.mechanism_manager.create_port_postcommit(mech_context)
> ...
> ...
> return result
>
> As a result, I need to carefully deal with the database nested transaction
> issue to prevent from db lock when I develop my own mechanism driver. Right
> now, I'm trying to get the idea behind the scene. Is it possible to
> refactor it in order to make precommit and postcommit out of the db
> transaction? I think it is perfect for those who develop mechanism driver
> and do not know well about the functioning context of the whole ML2 plugin.
>
> Thanks,
> Li Ma
>
> _______________________________________________
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>
>
>
>
> --
>
> Kevin Benton
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>
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>



-- 
Kevin Benton
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