I think we have enough people using Cassandra in production now that it would be useful to be explicit about the kinds of changes we will make between major and minor releases. Here is one possibility:
Minor releases (e.g. 0.4.0 -> 0.4.1): minor releases will contain bug fixes only -- no new functionality, full disk and network-level compatibility. If bugs cannot be fixed without adding new functionality or breaking compatibility, then it should probably not be fixed in the stable branch unless it is very severe. This is similar to postgresql's minor release policy, and I really like it for two reasons: (1) it makes a clear line of what people can expect in minor releases (2) making changes breaks stuff. That's just how software is, so the less we change in a stable branch the more likely it is that we won't introduce regressions. With our community's most enthusiastic testers also the most interested in trunk rather than older releases, it behooves us to be careful. Major releases (e.g. 0.5 -> 0.6): the compatibility story is going to be more nuanced: (1) sstable compatibility: may change. If it does, we will notify you in NEWS.txt and provide some method of upgrading without dump-and-reload (and hopefully without downtime while a conversion tool grinds away from old to new format, but I don't think we can promise that with 100% certainty at this point). (2) commitlog compatibility: may change. If it does, we will notify you in NEWS.txt that you need to "nodeprobe flush" before upgrading, as was the case for 0.4 -> 0.5. (3) network compatibility (from one cluster node to another): may change. If it does, we will notify you in NEWS.txt that you need to upgrade the whole cluster at once, as was the case for 0.4 -> 0.5. (4) thrift api: We will make our best efforts to keep deprecated methods will be available for one major release before being removed. (e.g., get_key_range is deprecated in 0.5; it will be removed in the next). I do not anticipate having to make the kind of changes we made from 0.3 to 0.4 (where we redid basically all the thrift structures, and there was really no sane way to provide backwards compatibility), but if we do we will notify you in NEWS.txt. (5) StorageProxy "fat client" api: This is still considered "mostly an internal api," to be used if you are brave and need the extra performance badly enough. :) We probably won't render it unrecognizably different since it's a fairly one-to-one mapping to the thrift api, which has the above compatibility policy, but no promises. Thoughts? (Separate threads to follow re "the next major release after 0.5 specifically," and "1.0.") -Jonathan
