[ovs-dev] [PATCH] ovs-xapi-sync: Cache the bridge-id value for non nicira-bridge-id too.

Ben Pfaff blp at nicira.com
Tue Jun 18 21:35:50 UTC 2013


On Tue, Jun 18, 2013 at 02:24:47PM -0700, Gurucharan Shetty wrote:
> On Tue, Jun 18, 2013 at 1:59 PM, Ben Pfaff <blp at nicira.com> wrote:
> 
> > On Tue, Jun 18, 2013 at 01:30:28PM -0700, Gurucharan Shetty wrote:
> > > On Tue, Jun 18, 2013 at 11:05 AM, Ben Pfaff <blp at nicira.com> wrote:
> > >
> > > > On Mon, Jun 17, 2013 at 01:25:01AM -0700, Gurucharan Shetty wrote:
> > > > > Currently we connect to xapi in case there are multiple
> > > > > external_ids:xs-network-uuids to get the single bridge id everytime
> > > > > we have a change in the database for all the interested columns in
> > > > > ovs-xapi-sync. The xs-network-uuids value can also change whenever
> > > > > new VLANs are added or deleted, which is a common use case. The
> > > > > disadvantage with this approach is that we query XAPI more often
> > > > > and set the bridge-id as "" if we don't get a valid response for
> > > > > our query. This can take down the logical connectivity for all the
> > > > > VMs on that xenserver.
> > > > >
> > > > > Instead of looking at the PIF records for all the xs-network-uuids,
> > > > > we can instead just look at the xapi record which has the same bridge
> > > > > name as the OVS bridge name and then cache its uuid. This value will
> > > > > hold true till the OVS bridge is recreated in which case we will
> > re-read
> > > > > the value.
> > > > >
> > > > > Signed-off-by: Gurucharan Shetty <gshetty at nicira.com>
> > > >
> > > > I think that the tolerance for XAPI failures is incomplete, because we
> > > > call update_fail_mode(), update_in_band_mgmt(), and get_bridge_id()
> > > > only once for a bridge, even if XAPI fails to respond on the first
> > > > attempt.
> > > >
> > > Yes. We can make some improvements. Do you mind, if I come up with a
> > > separate patch
> > > for this, since the current one talks about caching non nicira-bridge-id.
> > > (get_bridge_id() gets
> > > the nicira-bridge-id)
> >
> > OK.
> >
> > > > I am not sure why the set_external_id() call splits bridge_id on ';'.
> > > > Can bridge_id contain ';' at this point?
> > > >
> > > The case wherein bridge-id can have ";" is if nicira-bridge-id has a ";".
> > > If you feel, that is not a valid use case, I can get rid of it.
> >
> > I guess that it is existing code, so it is better not to change it,
> > especially in an unrelated patch.
> >
> > > > I am not sure why bridge_id and bridge_id_cache are different
> > > > variables.  When do they have different values?
> > > >
> > > In case get_single_bridge_id() gets us a "", we don't want to cache it.
> > > Hence 2 separate variables.
> >
> > I see.  "" != None even though Python treats both as false.
> >
> > This code is really confusing.  Every time I look at it, I get more
> > confused.
> >
> > I am probably doing something stupid here again, but how about this
> > version:
> >
> >         new_bridges = {}
> >         for row in idl.tables["Bridge"].rows.itervalues():
> >             bridge_id = bridges.get(row.name)
> >             if bridge_id is None:
> >                 # Configure the new bridge.
> >                 update_fail_mode(row)
> >                 update_in_band_mgmt(row)
> >
> >                 # Get the correct bridge_id, if we can.
> >                 bridge_id = get_bridge_id(row.name)
> >                 if bridge_id is None:
> >                     xs_network_uuids =
> > row.external_ids.get("xs-network-uuids")
> >                     if xs_network_uuids:
> >                         bridge_ids = xs_network_uuids.split(";")
> >                         if len(bridge_ids) == 1:
> >                             bridge_id = bridge_ids[0]
> >                         else:
> >                             bridge_id = get_single_bridge_id(bridge_ids,
> >                                                              row.name)
> >
> So in this case, we will not be setting the external_ids:bridge_id as "",
> if get_single_bridge_id() does not get correct records from xapi and we
> will simply retain the old value in the database. I guess, this was not
> your intent?

If our connection to XAPI is malfunctioning in some way, then I don't
know whether it is better to clear the database fields or retain them.
If you think that it is better to clear them, then I think something
very similar would work, maybe like this:

       new_bridges = {}
       for row in idl.tables["Bridge"].rows.itervalues():
            bridge_id = bridges.get(row.name)
            if bridge_id is None:
                # Configure the new bridge.
                update_fail_mode(row)
                update_in_band_mgmt(row)

                # Get the correct bridge_id, if we can.
                bridge_id = get_bridge_id(row.name)
                if bridge_id is None:
                    xs_network_uuids = row.external_ids.get("xs-network-uuids")
                    if xs_network_uuids:
                        bridge_ids = xs_network_uuids.split(";")
                        if len(bridge_ids) == 1:
                            bridge_id = bridge_ids[0]
                        else:
                            bridge_id = get_single_bridge_id(bridge_ids,
                                                             row.name)
            set_external_id(row, "bridge-id", bridge_id)

            if bridge_id is not None:
                new_bridges[row.name] = bridge_id
        bridges = new_bridges

That is, move the set_external_id call out of the final "if" (and get
rid of the 'split' because one cannot split None).



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