On Thu, Nov 19, 2020 at 11:50:57AM +0100, Dumitru Ceara wrote:
> On 11/19/20 5:15 AM, Ben Pfaff wrote:
> > On Tue, Nov 17, 2020 at 05:50:20PM +0100, Dumitru Ceara wrote:
> >> It is not correct for ovn-controller to pass the current SB_Global.nb_cfg
> >> value to ofctrl_put() if there are pending changes to conditional
> >> monitoring clauses (local or in flight).  It might be that after the
> >> monitor condition is acked by the SB, records that were added to the SB
> >> before SB_Global.nb_cfg was set are now sent as updates to
> >> ovn-controller.  These should be first installed in OVS before
> >> ovn-controller reports that it caught up with the current
> >> SB_Global.nb_cfg value.
> >>
> >> Also, ofctrl_put should not advance cur_cfg if there are flow updates in
> >> flight.

...

> > ovn-controller has changed (advanced?) to the point that I have trouble
> > understanding the code now.  I'm going to assume that you understand it
> > pretty well, but please allow me to ask a question here.  Will this
> 
> I'm doing my best but there are so many dependencies and side effects in
> the code..

DDlog might actually help with that, eventually.  It should allow us to
program in the problem domain, rather than writing a lot of code to
manage dependencies.

> > always manage to come up to date with some version of the sb, or is
> > there a chance that it never will report a consistent value if the sb
> > keeps changing quickly?  I wasn't able to figure that out with a quick
> > look.
> > 
> 
> Now, back to your question:
> 
> TLDR: If ovn-controller has to continuously change its monitor
> conditions I *think* there is a chance that it will never report that is
> caught up with a specific SB seqno.  However, I tried various scenarios
> (with quick SB updates or claiming/releasing OVS interfaces in quick
> succession) and I didn't manage to make "ovn-nbctl --wait=hv sync" block
> indefinitely.

That's good, empirically.

> Moreover, I think the question is if it's correct for ovn-controller to
> report it has caught up if there are unseen SB flows that correspond to
> its currently requested but not acked monitor condition?

I think the answer is "no", which means that the next question is, how
do we implement it properly?  I don't have an immediate answer.  The
database interfacing code is rather complex these days.
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