Thanks for bringing this up Arun. One of the issues is that we haven't been clear about what type of compatibility breakages are allowed, and which are not. For example, renaming FileSystem#open is incompatible, and not OK, regardless of the alpha/beta tag. Breaking a server/server APIs is OK pre-GA but probably not post GA, at least in a point release, or required for a security fix, etc. Configuration, data format, environment variable, changes etc can all be similarly incompatible. The issue we had in HADOOP-9151 was someone claimed it is not an incompatible change because it doesn't break API compatibility even though it breaks wire compatibility. So let's be clear about the types of incompatibility we are or are not permitting. For example, will it be OK to merge a change before 2.2.0-beta that requires an HDFS metadata upgrade? Or breaks client server wire compatibility? I've been assuming that changing an API annotated Public/Stable still requires multiple major releases (one to deprecate and one to remove), does the alpha label change that? To some people the "alpha", "beta" label implies instability in terms of quality/features, while to others it means unstable APIs (and to some both) so it would be good to spell that out. In short, agree that we really need to figure out what changes are permitted in what releases, and we should update the docs accordingly (there's a start here: http://wiki.apache.org/hadoop/Roadmap).
Note that the 2.0.0 alpha release vote thread was clear that we thought were all in agreement that we'd like to keep client/server compatible post 2.0 - and there was no push back. We pulled a number of jiras into the 2.0 release explicitly so that we could preserve client/server compatibility going forward. Here's the relevant part of the thread as a refresher: http://s.apache.org/gQ "2) HADOOP-8285 and HADOOP-8366 changed the wire format for the RPC envelope in branch-2, but didn't make it into this rc. So, that would mean that future alphas would not be protocol-compatible with this alpha. Per a discussion a few weeks ago, I think we all were in agreement that, if possible, we'd like all 2.x to be compatible for client-server communication, at least (even if we don't support cross-version for the intra-cluster protocols)" Thanks, Eli On Tue, Jan 29, 2013 at 12:56 PM, Arun C Murthy <a...@hortonworks.com> wrote: > Folks, > > There has been some discussions about incompatible changes in the > hadoop-2.x.x-alpha releases on HADOOP-9070, HADOOP-9151, HADOOP-9192 and few > other jiras. Frankly, I'm surprised about some of them since the 'alpha' > moniker was precisely to harden apis by changing them if necessary, borne out > by the fact that every single release in hadoop-2 chain has had incompatible > changes. This happened since we were releasing early, moving fast and > breaking things. Furthermore, we'll have more in future as move towards > stability of hadoop-2 similar to HDFS-4362, HDFS-4364 et al in HDFS and > YARN-142 (api changes) for YARN. > > So, rather than debate more, I had a brief chat with Suresh and Todd. Todd > suggested calling the next release as hadoop-2.1.0-alpha to indicate the > incompatibility a little better. This makes sense to me, as long as we are > clear that we won't make any further *feature* releases in hadoop-2.0.x > series (obviously we might be forced to do security/bug-fix release). > > Going forward, I'd like to start locking down apis/protocols for a 'beta' > release. This way we'll have one *final* opportunity post hadoop-2.1.0-alpha > to make incompatible changes if necessary and we can call it > hadoop-2.2.0-beta. > > Post hadoop-2.2.0-beta we *should* lock down and not allow incompatible > changes. This will allow us to go on to a hadoop-2.3.0 as a GA release. This > forces us to do a real effort on making sure we lock down for > hadoop-2.2.0-beta. > > In summary: > # I plan to now release hadoop-2.1.0-alpha (this week). > # We make a real effort to lock down apis/protocols and release > hadoop-2.2.0-beta, say in March. > # Post 'beta' release hadoop-2.3.0 as 'stable' sometime in May. > > I'll start a separate thread on 'locking protocols' w.r.t client-protocols > v/s internal protocols (to facilitate rolling upgrades etc.), let's discuss > this one separately. > > Makes sense? Thoughts? > > thanks, > Arun > > PS: Between hadoop-2.2.0-beta and hadoop-2.3.0 we *might* be forced to make > some incompatible changes due to *unforeseen circumstances*, but no more > gratuitous changes are allowed. >
