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From lars hofhansl <la...@apache.org>
Subject Re: Client-Server wire compatibility?
Date Thu, 05 Mar 2015 21:15:41 GMT
To take a step... The discussion was around whether we can generally break a new client talking
an old cluster.From a client-server perspective that should be OK (IMHO), and that is how
we stated it in the compatibility doc.
If the client-server protocol is broken in such a way that (f.e.) an new HMaster can no longer
access META on an old RegionServer we have broken server-server compatibility, which we said
we wouldn't in order to support rolling upgrades.
Re: negotiationg...
I have been saying the in first meeting we had about protobufs that we should build a client-server
negotiation phase where client and server agree on which version of the protocol they'll use
to communicate (provide the intersection between the sets of the supported version is not
empty).Back than I was the only one arguing in that direction. Stating that we'll only guarantee
an old client with a new server seemed to be the next best thing to be reasonably flexible
in how we evolve things and allowing users a no-downtime upgrade path.

An example is: We add a new RPC to HBase.When the new client is used against an old cluster,
it would need to be able to fail gracefully when that new RPC is used.If we only support the
old client against a new cluster we won't have that problem (and we'd be free to add new stuff
as we see fit, as long as we do break old RPCs)
As long as the servers do not use that RPC amongst each other, we have not broken server-server
compatibility, and hence we are able to make change like in a minor version.

Does this make sense? Is that what you guys had in mind? Or do think we need to be stricter?

-- Lars

      From: Nick Dimiduk <ndimiduk@gmail.com>
 To: hbase-dev <dev@hbase.apache.org> 
Cc: lars hofhansl <larsh@apache.org> 
 Sent: Thursday, March 5, 2015 12:37 PM
 Subject: Re: Client-Server wire compatibility?
   
On Thu, Mar 5, 2015 at 12:24 PM, Stack <stack@duboce.net> wrote:

On Thu, Mar 5, 2015 at 12:18 PM, lars hofhansl <larsh@apache.org> wrote:

> Then we have broken server-server compatibility, which the doc state we
> won't break for patch and minor versions.

What is broke? A 1.1 client can't scan a 1.0 meta?


My thinking is that the fall-back approach would enable the new client code to communicate
with either server version. Kind of a poor-man's feature negotiation protocol.
Can you elaborate Lars?



> -- Lars
>       From: Andrey Stepachev <octo47@gmail.com>
>  To: dev@hbase.apache.org
>  Sent: Thursday, March 5, 2015 9:48 AM
>  Subject: Re: Client-Server wire compatibility?
>
> Hi Nick,
>
> > I suppose it's possible the client in the master is never used outside of
> localhost, I haven't checked that bit.
>
> Client is definitely used to access meta, which can be hosted anywhere,
> so basically we can face with situation when master is upgraded and
> hits old region server.
>
>
>
> On Thu, Mar 5, 2015 at 5:21 AM, Nick Dimiduk <ndimiduk@gmail.com> wrote:
>
> > My point was that we cannot make this guarantee as there's a client
> > embedded in the master (and perhaps other places). We can't enforce the
> > order in which components are upgraded, which makes it possible for the
> new
> > client in the new master to reach out to an old RS during the rolling
> > upgrade.
> >
> > I suppose it's possible the client in the master is never used outside of
> > localhost, I haven't checked that bit.
> >
> > On Wednesday, March 4, 2015, lars hofhansl <larsh@apache.org> wrote:
> >
> > > The idea actually was that a new client can never be 100% supported,
> > since
> > > a user could use it accessing new features that the server does not
> > > understand.The reverse is always possible, since the old client can
> > expose
> > > anything new unduly we can always upgrade the server as old as it
> doesn't
> > > break the old client.
> > > Supporting both ways is too limiting I think, at least for minor
> version.
> > > For example we might want to add a *new* RPC.As long as we only support
> > old
> > > client with new servers we can do that. In any other combination that
> > would
> > > not (as easily) possible.
> > > That's why I phrased it only that way in my version proposal.
> > >
> > > For patch releases it's reasonable to support it both ways.The book is
> > > currently unavailable from the HBase site, so I can't check the exact
> > > wording we ended up with.
> > >
> > > -- Lars
> > >      From: Nick Dimiduk <ndimiduk@gmail.com <javascript:;>>
> > >  To: hbase-dev <dev@hbase.apache.org <javascript:;>>
> > >  Sent: Wednesday, March 4, 2015 4:49 PM
> > >  Subject: Re: Client-Server wire compatibility?
> > >
> > > I believe your posted example is intended to be supported. There's no
> > > enforcement, for instance, that the master is upgraded before all RS's.
> > >
> > >
> > >
> > > On Wed, Mar 4, 2015 at 4:06 PM, Matteo Bertozzi <
> theo.bertozzi@gmail.com
> > > <javascript:;>>
> > > wrote:
> > >
> > > > the book (http://hbase.apache.org/book.html#hbase.versioning)
> > > > talks about "only allow upgrading the server first" to use new APIs.
> > > >
> > > > what about a new client talking to an old server for "old"
> operations?
> > > > For example: If I have a 1.1 client, can I ask a 1.0 server to
> create a
> > > > table?
> > > >
> > >
> > >
> > >
> >
>
>
>
> --
> Andrey.
>
>
>
>




  
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