Perhaps clients should always send the oldest version of the metadata
request which supports KIP-35 when initially connecting to the cluster.
Depending on the versions in the response, it can upgrade to a more recent
version. Then maybe we don't need the empty response hack?
One thing that's not clear to me is whether the ultimate goal of this KIP
is to have our clients support multiple broker versions. It would be a
little weird to have this feature if our own clients don't use it.
-Jason
On Mon, Mar 14, 2016 at 3:34 PM, Ashish Singh <asi...@cloudera.com> wrote:
> On Mon, Mar 14, 2016 at 2:12 PM, Ismael Juma <ism...@juma.me.uk> wrote:
>
> > On Mon, Mar 14, 2016 at 8:45 PM, Gwen Shapira <g...@confluent.io> wrote:
> > >
> > > > I don't see how it helps. If the client is communicating with a
> broker
> > > that
> > > > does not support KIP-35, that broker will simply close the
> connection.
> > If
> > > > the broker supports KIP-35, then it will provide the broker version.
> I
> > > > don't envisage a scenario where a broker does not support KIP-35, but
> > > > implements the new behaviour of sending an empty response. Do you?
> > > >
> > > > Are you sure about that? Per KIP-35, the broker supplies the version
> in
> > > response to Metadata request, not in response to anything else.
> > > If the client sends producer request version 42 (accidentally or due to
> > > premature upgrade) to KIP-35-compactible broker - we want to see an
> empty
> > > packet and not a connection close.
> > > Sending a broker version was deemed impractical IIRC.
> > >
> >
> > OK, so this is a different case than the one Ashish described ("client
> that
> > wants to support broker versions that do not provide broker version in
> > metadata and broker versions that provides version info in metadata").
> So,
> > you are suggesting that if a client is communicating with a broker that
> > implements KIP-35 and it receives an empty response, it will assume that
> > the broker doesn't support the request version and it won't try to parse
> > the response? I think it would be good to explain this kind of thing in
> > detail in the KIP.
> >
> Actually even in this case and the case I mentioned, closing connection
> should be fine. Lets think about possible reasons that could lead to this
> issue.
>
> 1. Client has incorrect mapping of supported protocols for a broker
> version.
> 2. Client misread broker version from metadata response.
> 3. Client constructed unsupported protocol version by mistake.
>
> In all the above cases irrespective of what broker does, client will keep
> sending wrong request version.
>
> At this point, I think sending an empty packet instead of closing
> connection is a nice to have and not mandatory requirement. Like in the
> above case, a client can catch parsing error and be sure that there is
> something wrong in the protocol version it is sending. However, a generic
> connection close does not really provide any information on probable cause.
>
> What do you guys suggest?
>
> >
> > Ismael
> >
>
>
>
> --
>
> Regards,
> Ashish
>
