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Hi Michael,

Yes, it's a similar issue but different aspect. Actually, the case for l2gw
is worse, considering we have to deal with 2 existing back-end driver which
have different understanding for the interfaces. But I think the proposed
approach for networking-ovn is inspiring and helpful for l2gw.

Thanks,

On Fri, Dec 8, 2017 at 11:59 PM, Michael Bayer <mbayer at redhat.com> wrote:

> On Wed, Dec 6, 2017 at 3:46 AM, Peng Liu <pliu at redhat.com> wrote:
> > Hi,
> >
> > During working on this patch[0], I encounter some DB out-of-sync
> problem. I
> > think maybe the design can be improved. Here is my thought, all comments
> are
> > welcome.
>
>
> see also https://review.openstack.org/#/c/490834/ which I think is
> dealing with a similar (if not the same) issue.
>
> >
> > In plugin code, I found all the resource operations follow the pattern in
> > [1]. It is a very misleading design compare to [2].
> >
> > "For every action that can be taken on a resource, the mechanism driver
> > exposes two methods - ACTION_RESOURCE_precommit, which is called within
> the
> > database transaction context, and ACTION_RESOURCE_postcommit, called
> after
> > the database transaction is complete."
> >
> > In result, if we focus on the out-of-sync between plugin DB and
> > driver/backend DB:
> >
> > 1) In RPC driver, only methods Action_Resource and are implemented. Which
> > means the action is token before it was written in plugin DB. In case of
> > action partial succeed (especially for update case) or plugin DB
> operation
> > failure, it will cause DB out-of-sync.
> > 2) In ODL driver, only methods Action_Resource_postcommit are
> implemented,
> > which means there is no validation in ODL level before the record is
> written
> > in the plugin DB. In case of, ODL side failure, there is no rollback for
> > plugin DB.
> >
> > So, to fix this issue is costly. Both plugin and driver sides need to be
> > altered.
> >
> > The other side of this issue is a period db monitor mechanism between
> plugin
> > and drivers, and it is another story.
> >
> >
> > [0] https://review.openstack.org/#/c/516256
> > [1]
> > ...
> >     def Action_Resource
> >         self.validate_Resource_for_Action
> >         self.driver.Action_Resource
> >         with context.session.begin(subtransactions=True):
> >             super.Action_Resource
> >             self.driver.Action_Resource_precommit
> >         try:
> >             self.driver.Action_Resource_postcommit
> > ...
> > [2] https://wiki.openstack.org/wiki/Neutron/ML2
> >
> > --
> > Peng Liu
> >
> > ____________________________________________________________
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Peng Liu | Senior Software Engineer

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