>
> Are you suggesting this as a solution for the problem where a KIP-35 aware
> client sends a higher version of metadata req, say v2, to a KIP-35 aware
> broker that only supports up to v1.
Yes, that's right. In that case, the client first sends v1, finds out that
the broker supports v2, and then sends v2 (if it has any reason to do so).
We had a bit of discussion on such scenarios, and it seemed to be a chicken
> and egg problem that is hard to avoid. Your suggestion definitely makes
> sense, however it falls under the purview of clients.
That basically means clients should figure it out for themselves? Might be
nice to have a better answer.
KIP-35 only aims on adding support for getting the version info from a
> broker. This definitely can be utilized by our clients. However, that can
> follow KIP-35 changes. Does this sound reasonable to you?
It may be OK, but I'm a little concerned about offering a feature that we
don't support ourselves. Sometimes it's not until implementation that we
find out whether it really works as expected. And if we're eventually
planning to support it, I feel we should think through some of the cases a
bit more. For example, the upgrade and downgrade cases that Becket
mentioned earlier. It doesn't feel too great to support this feature unless
we can offer guidance on how to use it.
-Jason
On Mon, Mar 14, 2016 at 4:20 PM, Ashish Singh <asi...@cloudera.com> wrote:
> Hi Jason,
>
> On Mon, Mar 14, 2016 at 4:04 PM, Jason Gustafson <ja...@confluent.io>
> wrote:
>
> > 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?
> >
> Are you suggesting this as a solution for the problem where a KIP-35 aware
> client sends a higher version of metadata req, say v2, to a KIP-35 aware
> broker that only supports up to v1.
>
> We had a bit of discussion on such scenarios, and it seemed to be a chicken
> and egg problem that is hard to avoid. Your suggestion definitely makes
> sense, however it falls under the purview of clients.
>
> >
> > 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.
> >
> KIP-35 only aims on adding support for getting the version info from a
> broker. This definitely can be utilized by our clients. However, that can
> follow KIP-35 changes. Does this sound reasonable to you?
>
> >
> > -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
> > >
> >
>
>
>
> --
>
> Regards,
> Ashish
>
