[ovs-dev] [PATCH v3] ovn-controller: Omit alert for Port_Binding.external_ids changes

[Ben Pfaff]

On Thu, Jun 27, 2019 at 12:43:18AM +0530, Numan Siddique wrote:
> On Thu, Jun 27, 2019 at 12:19 AM Ben Pfaff <blp at ovn.org> wrote:
> 
> > On Wed, Jun 26, 2019 at 07:46:25PM +0530, nusiddiq at redhat.com wrote:
> > > From: Numan Siddique <nusiddiq at redhat.com>
> > >
> > > Running the command "ovn-nbctl set logical_switch_port foo
> > external_ids:foo=bar"
> > > results in the incremetal processing engine to recompute the flows on the
> > > chassis where the logical port 'foo' is claimed.
> > >
> > > This patch avoids this unnecessary recomputation by omitting the alert
> > for the
> > > Port_Binding.external_ids column.
> > >
> > > Signed-off-by: Numan Siddique <nusiddiq at redhat.com>
> > > Acked-by: Han Zhou <hzhou8 at ebay.com>
> > > ---
> > >
> > > v2 -> v3
> > > ------
> > >   * Based on the review comments from Han, dropped p2 and p3 from the
> > series.
> >
> > This only omits the alert for external-ids from one table.  I think that
> > ovn-controller should not look at the external_ids in most tables.  The
> > only ones I see it dealing with are: the one on Chassis, which seems
> > legitimate (it is only setting keys there, and the behavior is
> > documented) and external_ids:dns_id in the DNS table, which makes me
> > suspicious because it appears that it's an undocumented communication
> > channel from ovn-northd to ovn-controller.  I think that all the others
> > can omit alerts.
> >
> 
> To sync the dns entries from nb db to sb db, we store the uuid of nb db dns
> row in sb db.
> I will submit a doc patch for this. Thanks for pointing this out.

OK.

external-ids fields are intended for use by higher-level systems
(e.. ovn-northd in the case of sbdb) to keep notes on how to associate
entities in a database with corresponding higher-level entities
(e.g. nbdb, in this case).  This means that the lower-level software
(e.g. ovn-controller, in this case) don't normally read the external-ids
fields since they don't have any way to interpret it.  Usually, if an
external-ids key is being used to communicate between higher and lower
level systems, it is a mistake: there should be some other interface for
the purpose, such as a dedicated column.

> > However, why just omit alerts?  If ovn-controller does not read these
> > (it should not), then they may be omitted entirely.
> >
> Right?
> >
> 
> That's right. I don't understand the alert APIs properly. I will check it
> and update the patch to omit
> tracking the external_ids of all tables.

I guess they weren't explained very well.  I sent out what I hope
improves it:
https://mail.openvswitch.org/pipermail/ovs-dev/2019-June/360140.html