Re: define backwards compatibility

[Doug Cutting <cu...@apache.org>]

Joydeep Sen Sarma wrote:
> i find the confusion over what backwards compatibility means scary - and i am really hoping that the outcome of this thread is a clear definition from the committers/hadoop-board of what to reasonably expect (or not!) going forward.

The goal is clear: code that compiles and runs warning-free in one 
release should not have to to be altered to try the next release.  It 
may generate warnings, and these should be addressed before another 
upgrade is attempted.

Sometimes it is not possible to achieve this.  In these cases 
applications should fail with a clear error message, either at 
compilation or runtime.

In both cases, incompatible changes should be well documented in the 
release notes.

This is described (in part) in http://wiki.apache.org/hadoop/Roadmap

That's the goal.  Implementing and enforcing it is another story.  For 
that we depend on developer and user vigilance.  The current issue seems 
a case of failure to implement the policy rather than a lack of policy.

Doug