[ovs-dev] OVN: RFC add a new JSON-RPC selective monitoring method

[Ben Pfaff]

On Mon, Aug 31, 2015 at 01:19:35PM +0300, Liran Schour wrote:
> Following the discussion on overcoming OVN scalability issues by allowing 
> clients to monitor only rows that meet specific criteria
> (http://openvswitch.org/pipermail/dev/2015-August/059149.html), I propose 
> to amend the OVSDB protocol specification (RFC 7047). 
> 
> Proposed amendment is to define a new monitor method, monitor_cond, for 
> specifying monitoring conditions. Adding a new method allows keeping all 
> of the existing client code intact, replacing code only in places that can 
> benefit from this new method (e.g. in ovn-controller).
> 
> Below is the description for a new JSON-RPC monitor_cond method to be 
> added to the OVSDB protocol. (All references are to RFC 7047)

Thanks.  I have some comments.

First, this drops the "columns" member.  Why?  I see no other way to
specify which columns are monitored.

Second, this isn't entirely clear about how to consider the conditions,
because a condition can be true before a row is modified and false
afterward, and vice versa.  Presumably, when a row becomes covered by a
condition (after its initial insertion), or when a row is no longer
covered by a condition (even though it has not be deleted), the client
should be notified.

Third, this may be a good opportunity to fix a design mistake in
"monitor", which is that it sends too much data when a row is modified:
it sends both the old and new values for columns that have changed, as
well as the value of every column that did not change.  I thought that
would be useful when I originally designed it, but it's proven to just
waste CPU and memory and bandwidth.

Thanks,

Ben.