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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Release1.0Requirements" by SanjayRadia
Date Thu, 09 Oct 2008 20:41:25 GMT
Dear Wiki user,

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The following page has been changed by SanjayRadia:

  '' Doug, currently when a new RPC method is added, we declare a change in protocol version
and old and new can no long talk via rpc. There are two issues.  One is the wire compatibility
as you noted (this is new). Second is that when we add new rpc methods, the client side library
can use the new rpc method but it must fall back on old rpc methods when talking to old servers
(this must be explicitly coded in the library -- it won't happen just by introducing wire
compatibility).  You are right in that is nothing new as far as API compatibility.  Maybe
this point is obvious to most, but Owen and I discussed it at some length and thought it was
a subtle twist that our developers will have to be aware of in 1.0.''
  ''Sanjay, we should vote on this as a change to our back-compatibility policy, and, if it
passes, start enforcing it.  --DougCutting''
+ ''I am not sure if we as community can start enforcing protocol compatibility right away
because in order to do that we would have to version the rpc parameters. One we version the
data types we can change the policy and enforce it.
+ However we can easily support backward compatibility when new methods are added. I am not
sure if this subset can be documented in the
+ backward-compatibility policy (more correctly I don't know how to word it); however I will
file a jira to change the rpc layer to detect and throw exceptions on missing methods. I will
also follow that up with a patch for that jira. This will allow is us to treat the addition
of a new method as a backward compatible changes that does not require the version # to be
  === Time frame for 1.0 to 2.0 ===
  What is the expectation for life of 1.0 before it goes to 2.0 Clearly if we switch from
1.0 to 2.0 in 3 months the compatibility benefit of 1.0 does not deliver much value for Hadoop
customers. A time frame of 12 months is probably the minimum.

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