On Tue, Apr 10, 2018 at 6:21 PM, Han Zhou <zhou...@gmail.com> wrote:
>
>
>
> On Tue, Apr 10, 2018 at 5:04 PM, Ben Pfaff <b...@ovn.org> wrote:
> >
> > On Fri, Apr 06, 2018 at 02:40:21PM -0700, Han Zhou wrote:
> > > On Fri, Apr 6, 2018 at 1:54 PM, Ben Pfaff <b...@ovn.org> wrote:
> > > >
> > > > Thanks for working on making OVN faster and scale better.
> > > >
> > > > I see what you mean about how nb_cfg can be a scale problem.
Really,
> > > > each hypervisor only cares about its own row, but each of them is
being
> > > > notified about the current value in every row.  Ideally, we want
the HVs
> > > > to be able to say to ovsdb-server, "Give me all the data in the
Chassis
> > > > table, except don't bother with nb_cfg in any rows except my own
row."
> > > >
> > > > Actually, there's a way for ovn-controller to do that: the OVSDB
> > > > protocol definition of monitor_cond allows the client to specify
> > > > multiple sets of columns to monitor in a table, and each set of
columns
> > > > has an independently attached condition.  This can be used to
specify
> > > > that most of the columns are monitored unconditionally but nb_cfg is
> > > > monitored only for a particular row.
> > > >
> > > > But there are still problems:
> > > >
> > > > 1. The implementation in ovsdb-server looks broken.  I don't think
it
> > > >    implements the spec.  It certainly isn't tested--none of the
existing
> > > >    clients ever passes more than a single set of columns.  I think
that
> > > >    it will work if all the sets of columns use the same condition,
but
> > > >    that doesn't help with this case.  It will need to be fixed.
> > > >
> > > > 2. The client implementation in ovsdb-idl doesn't anticipate
difference
> > > >    conditions for different columns.  It will need to be enhanced to
> > > >    support this use.
> > > >
> > > > In the short term this is going to be more work than just creating
a new
> > > > table.  In the long term, though, it will allow us to be more
flexible
> > > > and more agile, since improvements similar to the one in this patch
will
> > > > require only client changes, not database schema changes.
> > > >
> > > > Comments?
> > >
> > > Thanks for the valuable information! I didn't even know that ovsdb is
> > > supposed to support multiple set columns with different monitor
conditions.
> > > It surely would be the right way to go if it is supported. However,
as you
> > > mentioned the mechanism doesn't work yet and I am not sure how much
work is
> > > needed to make it work, it seems reasonable to me to "workaround" it
at
> > > least for short term until that is ready in the future. Then we could
> > > simply resurrect the old column in the old table with the new monitor
> > > conditions. What do you think?
> >
> > This kind of workaround would essentially persist forever.  We'd never
> > be able to get rid of it--or, more to the point, we would never be able
> > to justify the work.  We'd be stuck with something ugly.
> >
> > So: if you think the workaround is valuable, then one way to justify it
> > would be to reformulate it in a way that isn't so ugly.  As currently
> > written, when a person looks at the table structure, (s)he notices a
> > table that has a single column and is named for that single column.
> > That sticks out, clearly, as some kind of compromise, and the
> > documentation even calls it out as an optimization.  But there might be
> > a logical, conceptual reason why it makes sense to have a separate table
> > for some kinds of chassis-related data.  If there is, then that would
> > suggest a name for the table, and for the class of data that should
> > should go in there, and it would make it possible to have something that
> > is both faster and a reasonable design.
> >
> > I'm not saying that there is necessarily a logical, conceptual reason
> > that one can come up here, but if there is then it would certainly make
> > it much easier to support the patch.
>
> Hi Ben, I'm not sure if I got your point completely. A logical reason for
this separate table might be for holding chassis private data, the data
that other chassis is not interested in. Of course the reason for holding
such private data in a separate table is still this huge performance
difference as it is shown in the test result. So I think the table can be
named as Chassis_Private_Data, and I can document in ovn-sb.xml more about
the performance considerations, and the future improvement about the
monitor_cond. Would this address your point or did I totally missed your
point?
>
Hi Ben, could you confirm so that I can work on v3?

> Thanks,
> Han
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