Cassandra 2.1 was released in September, which means that if we were on track with our stated goal of six month releases, 3.0 would be done about now. Instead, we haven't even delivered a beta. The immediate cause this time is blocking for 8099 <https://issues.apache.org/jira/browse/CASSANDRA-8099>, but the reality is that nobody should really be surprised. Something always comes up -- we've averaged about nine months since 1.0, with 2.1 taking an entire year.
We could make theory align with reality by acknowledging, "if nine months is our 'natural' release schedule, then so be it." But I think we can do better. Broadly speaking, we have two constituencies with Cassandra releases: First, we have the users who are building or porting an application on Cassandra. These users want the newest features to make their job easier. If 2.1.0 has a few bugs, it's not the end of the world. They have time to wait for 2.1.x to stabilize while they write their code. They would like to see us deliver on our six month schedule or even faster. Second, we have the users who have an application in production. These users, or their bosses, want Cassandra to be as stable as possible. Assuming they deploy on a stable release like 2.0.12, they don't want to touch it. They would like to see us release *less* often. (Because that means they have to do less upgrades while remaining in our backwards compatibility window.) With our current "big release every X months" model, these users' needs are in tension. We discussed this six months ago, and ended up with this: What if we tried a [four month] release cycle, BUT we would guarantee that > you could do a rolling upgrade until we bump the supermajor version? So 2.0 > could upgrade to 3.0 without having to go through 2.1. (But to go to 3.1 > or 4.0 you would have to go through 3.0.) > Crucially, I added Whether this is reasonable depends on how fast we can stabilize releases. > 2.1.0 will be a good test of this. > Unfortunately, even after DataStax hired half a dozen full-time test engineers, 2.1.0 continued the proud tradition of being unready for production use, with "wait for .5 before upgrading" once again looking like a good guideline. I’m starting to think that the entire model of “write a bunch of new features all at once and then try to stabilize it for release” is broken. We’ve been trying that for years and empirically speaking the evidence is that it just doesn’t work, either from a stability standpoint or even just shipping on time. A big reason that it takes us so long to stabilize new releases now is that, because our major release cycle is so long, it’s super tempting to slip in “just one” new feature into bugfix releases, and I’m as guilty of that as anyone. For similar reasons, it’s difficult to do a meaningful freeze with big feature releases. A look at 3.0 shows why: we have 8099 coming, but we also have significant work done (but not finished) on 6230, 7970, 6696, and 6477, all of which are meaningful improvements that address demonstrated user pain. So if we keep doing what we’ve been doing, our choices are to either delay 3.0 further while we finish and stabilize these, or we wait nine months to a year for the next release. Either way, one of our constituencies gets disappointed. So, I’d like to try something different. I think we were on the right track with shorter releases with more compatibility. But I’d like to throw in a twist. Intel cuts down on risk with a “tick-tock” schedule for new architectures and process shrinks instead of trying to do both at once. We can do something similar here: One month releases. Period. If it’s not done, it can wait. *Every other release only accepts bug fixes.* By itself, one-month releases are going to dramatically reduce the complexity of testing and debugging new releases -- and bugs that do slip past us will only affect a smaller percentage of users, avoiding the “big release has a bunch of bugs no one has seen before and pretty much everyone is hit by something” scenario. But by adding in the second rule, I think we have a real chance to make a quantum leap here: stable, production-ready releases every two months. So here is my proposal for 3.0: We’re just about ready to start serious review of 8099. When that’s done, we branch 3.0 and cut a beta and then release candidates. Whatever isn’t done by then, has to wait; unlike prior betas, we will only accept bug fixes into 3.0 after branching. One month after 3.0, we will ship 3.1 (with new features). At the same time, we will branch 3.2. New features in trunk will go into 3.3. The 3.2 branch will only get bug fixes. We will maintain backwards compatibility for all of 3.x; eventually (no less than a year) we will pick a release to be 4.0, and drop deprecated features and old backwards compatibilities. Otherwise there will be nothing special about the 4.0 designation. (Note that with an “odd releases have new features, even releases only have bug fixes” policy, 4.0 will actually be *more* stable than 3.11.) Larger features can continue to be developed in separate branches, the way 8099 is being worked on today, and committed to trunk when ready. So this is not saying that we are limited only to features we can build in a single month. Some things will have to change with our dev process, for the better. In particular, with one month to commit new features, we don’t have room for committing sloppy work and stabilizing it later. Trunk has to be stable at all times. I asked Ariel Weisberg to put together his thoughts separately on what worked for his team at VoltDB, and how we can apply that to Cassandra -- see his email from Friday <http://bit.ly/1MHaOKX>. (TLDR: Redefine “done” to include automated tests. Infrastructure to run tests against github branches before merging to trunk. A new test harness for long-running regression tests.) I’m optimistic that as we improve our process this way, our even releases will become increasingly stable. If so, we can skip sub-minor releases (3.2.x) entirely, and focus on keeping the release train moving. In the meantime, we will continue delivering 2.1.x stability releases. This won’t be an entirely smooth transition. In particular, you will have noticed that 3.1 will get more than a month’s worth of new features while we stabilize 3.0 as the last of the old way of doing things, so some patience is in order as we try this out. By 3.4 and 3.6 later this year we should have a good idea if this is working, and we can make adjustments as warranted. -- Jonathan Ellis Project Chair, Apache Cassandra co-founder, http://www.datastax.com @spyced
