Re: CEP-15 Update

[C. Scott Andreas]

I’m also supportive of proceeding to merge. The CEP contributors have worked incredibly hard on the protocol and feature and I’m proud it’s reached this point. If the concern is trunk stability - we have been deploying trunk-derived builds for over six months and will continue to do so post-merge. Maintaining a stable trunk is incredibly important to me and will remain so. I’m not sure if others have taken the step of deploying trunk. But it’s helped us immensely in maintaining continuous and incremental confidence in what’s landing in top of tree, and enabled us to identify and resolve issues much more quickly. The CEP authors have a huge interest in maintaining a stable trunk. Most databases would have a build engineering team the size of the CEP team focused on rebases and integration. I can attest to the challenge of continuing to maintain separate source trees. I believe the work has reached a level of completeness that integration into trunk is the best next step for continued development, performance, and polish. I also believe there is more value generated for the project and its users by proceeding to merge than delaying to a potential future merge window which may be some time away. – Scott On Mar 6, 2025, at 9:54 PM, Benedict <bened...@apache.org> wrote:  There are essentially three possible timelines to choose from here:  1) We agree in the next few days to merge to trunk. We will then prioritise rebasing onto trunk and resolving any pre-merge items starting next week. 2) There’s some more debate and agreement to merge to trunk in a week or two. In the meantime we will shift to internal-first development but we’ll likely prioritise the above work as soon as we can, which may be in a few weeks, so we can shift to trunk first development. 3) We don’t agree to merge accord anytime soon, so we shift to internal-first development for the time being. I’m not sure when we will prioritise any of the above. Our resources are finite and we’ve exhausted them (literally), so it’s pretty much pick one of the above. I don’t really mind which you pick, but I won’t personally be prioritising merge after this third attempt. On 6 Mar 2025, at 22:01, Jon Haddad <j...@rustyrazorblade.com> wrote:  Hmm... I took a look at the cep-15-accord branch in GitHub, it looks like it's several hundred commits behind trunk.  Since you'll need to rebase again before merge *anyways*, would it make sense to do it once more, and I can publish easy-cass-lab with the latest branch?  If folks have concerns, it's easy to fire up a cluster (I do it constantly) and try it out. I think if we were to do this, out of consideration we should time box the amount of time for an evaluation and unless someone raises an objection, consider lazy consensus achieved. Jon On Thu, Mar 6, 2025 at 12:46 PM Benedict Elliott Smith <bened...@apache.org> wrote: Because we want to validate against the latest code in trunk, else we are validating stale behaviours. The cost of rebasing is high, so we do not do it frequently. That means we will likely stop developing OSS-first, as the focus will have to move to our internal branch that satisfies these criteria. Exactly what this might be for upstreaming I cannot say. Personally, I aim to work exclusively on the branch we are stabilising. If that is not trunk, the latency for my contributions being made public might be high, as I have a huge imbalance of over-investment to recoup, and anything unnecessary will be deferred. Since the feature is disabled, and the code is almost entirely isolated, I cannot imagine the cost to the community to removing this work would be very high. But, I do not intend to argue Accord’s case here. I will let you all decide. Please decide soon though, as it shapes our work planning. The positive reception so far had lead me to consider prioritising a move to trunk-first development within the next week or two, and the associated work that entails. However, if that was optimistic we will have to shift our plans. On 6 Mar 2025, at 20:16, Jordan West <jw...@apache.org> wrote: The work and effort in accord has been amazing. And I’m sure it sets a new standard for code quality and correctness testing which I’m also entirely behind. I also trust the folks working on it want to take it to the a fully production ready solution. But I’m worried about circumstances out of our control leaving us with a very complex feature that isn’t complete.  I do have some questions. Could folks help me better understand why testing real workloads necessitates a merge (my understanding from the original reason is this is the impetus for why we would merge now)? Also I think the performance and scheme change caveats are rather large ones. One of accords promise was better performance and I think making schema changes with nodes down not being supported is a big gap. Could we have some criteria like “supports all the operations PaxosV2 supports” or “performs as well or better than PaxosV2 on [workload(s)]”?  I understand waiting asks a lot of the authors in terms of baring the burden of a more complex merge. But I think we also need to consider what merging is asking the community to bear if the worst happens and we are unable to take the feature from its current state to something that can be widely used in production. Jordan  On Wed, Mar 5, 2025 at 15:52 Blake Eggleston <bl...@ultrablake.com> wrote: +1 to merging it On Wed, Mar 5, 2025, at 12:22 PM, Patrick McFadin wrote: You have my +1 On Wed, Mar 5, 2025 at 12:16 PM Benedict <bened...@apache.org> wrote: > > Correct, these caveats should only apply to tables that have opted-in to accord. > > On 5 Mar 2025, at 20:08, Jeremiah Jordan <jerem...@apache.org> wrote: > >  > So great to see all this hard work about to pay off! > > On the questions/concerns front, the only concern I would have towards merging this to trunk is if any of the caveats apply when someone is not using Accord.  Assuming they only apply when the feature flag is enabled, I see no reason not to get this merged into trunk once everyone involved is happy with the state of it. > > -Jeremiah > > On Mar 5, 2025 at 12:15:23 PM, Benedict Elliott Smith <bened...@apache.org> wrote: >> >> That depends on all of you lovely people :D >> >> I think we should have finished merging everything we want before QA by ~Monday; certainly not much later. >> >> I think we have some upgrade and python dtest failures to address as well. >> >> So it could be pretty soon if the community is supportive. >> >> On 5 Mar 2025, at 17:22, Patrick McFadin <pmcfa...@gmail.com> wrote: >> >> >> What is the timing for starting the merge process? I'm asking because >> >> I have (yet another) presentation and this would be a cool update. >> >> >> On Wed, Mar 5, 2025 at 1:22 AM Benedict Elliott Smith >> >> <bened...@apache.org> wrote: >> >> > >> >> > Thanks everyone. >> >> > >> >> > Jon - your help will be greatly appreciated. We’ll let you know when we’ve got the cycles to invest in performance work (hopefully fairly soon). I expect the first step will be improving visibility so we can better understand what the system is doing (particularly the caching layers), but we can dig in together when ready. >> >> > >> >> > On 4 Mar 2025, at 18:15, Jon Haddad <j...@rustyrazorblade.com> wrote: >> >> > >> >> > Very exciting! >> >> > >> >> > I have a client that's very interested in Accord, so I should have budget to dig into it, especially on the performance side of things. >> >> > >> >> > Jon >> >> > >> >> > On Tue, Mar 4, 2025 at 9:57 AM Dmitry Konstantinov <netud...@gmail.com> wrote: >> >> >> >> >> >> Thank you to all Accord and TCM contributors, it is really exciting to see a development of such huge and wonderful features moving forward and opening the door to the new Cassandra epoch! >> >> >> >> >> >> On Tue, 4 Mar 2025 at 20:45, Blake Eggleston <bl...@ultrablake.com> wrote: >> >> >>> >> >> >>> Thanks Benedict! >> >> >>> >> >> >>> I’m really excited to see accord reach this milestone, even with these caveats. You seem to have left yourself off the list of contributors though, even though you’ve been a central figure in its development :) So thanks to all accord & tcm contributors, including Benedict, for making this possible! >> >> >>> >> >> >>> On Tue, Mar 4, 2025, at 8:00 AM, Benedict Elliott Smith wrote: >> >> >>> >> >> >>> Hi everyone, >> >> >>> >> >> >>> It’s been exactly 3.5 years since the first commit to cassandra-accord. Yes, really, it’s been that long. >> >> >>> >> >> >>> We will be starting to validate the feature against real workloads in the near future, so we can’t sensibly push off merging much longer. The following is a brief run-down of the state of play. There are no known bugs, but there remain a number of caveats we will be incrementally addressing in the run-up to a full release: >> >> >>> >> >> >>> [1] Accord is likely to be SLOW until further optimisations are implemented >> >> >>> [2] Schema changes have a number of hard edges >> >> >>> [3] Validation is ongoing, so there are likely still a number of bugs to shake out >> >> >>> [4] Many operator visibility/tooling/documentation improvements are pending >> >> >>> >> >> >>> To expand a little: >> >> >>> >> >> >>> [1] As of the last experiment we conducted, accord’s throughput was poor - also leading to higher LAN latencies. We have done no WAN experiments to date, but the protocol guarantees should already achieve better round-trip performance, in particular under contention. Improving throughput will be the main focus of attention once we are satisfied the protocol is otherwise stable, but our focus remains validation for the moment. >> >> >>> [2] Schema changes have not yet been well integrated with TCM. Dropping a table for instance will currently cause problems if nodes are offline. >> >> >>> [3] We have a range of validations we are already performing against cassandra-accord directly, and against its integration with Cassandra in cep-15-accord. We have run hundreds of billions of simulated transactions, and are still discovering some minor fault every few billion simulated transactions or so. There remains a lot more simulated validation to explore, as well as with real clusters serving real workloads. >> >> >>> [4] There are already a range of virtual tables for exploring internal state in Accord, and reasonably good metric support. However, tracing is not yet supported, and our metric and virtual table integrations need some further development. >> >> >>> [5] There are also other edge cases to address such as ensuring we do not reuse HLCs after restart, supporting ByteOrderPartitioner, and live migration from/to Paxos is undergoing fine-tuning and validation; probably there are some other things I am forgetting. >> >> >>> >> >> >>> Altogether the feature is fairly mature, despite these caveats. This is the fruit of the labour of a long list of contributors, including Aleksey Yeschenko, Alex Petrov, Ariel Weisberg, Blake Eggleston, Caleb Rackliffe and David Capwell, and represents a huge undertaking. It also wouldn’t have been possible without the work of Alex Petrov, Marcus Eriksson and Sam Tunnicliffe on delivering transactional cluster metadata. I hope you will join me in thanking them all for their contributions. >> >> >>> >> >> >>> Alex has also kindly produced some initial overview documentation for developers, that can be found here: https://github.com/apache/cassandra/blob/cep-15-accord/doc/modules/cassandra/pages/developing/accord/index.adoc. This will be expanded as time permits. >> >> >>> >> >> >>> Does anyone have any questions or concerns? >> >> >>> >> >> >>> >> >> >> >> >> >> >> >> >> -- >> >> >> Dmitry Konstantinov >> >> > >> >> > >> >>