The TCM work (CEP-21) is in its review stage but being well past our cut-off date¹ for merging, and now jeopardising 5.0 GA efforts, I would like to propose the following.
We merge TCM and Accord only to trunk. Then branch cassandra-5.1 and cut an immediate 5.1-alpha1 release. I see this as a win-win scenario for us, considering our current situation. (Though it is unfortunate that Accord is included in this scenario because we agreed it to be based upon TCM.) This will mean… - We get to focus on getting 5.0 to beta and GA, which already has a ton of features users want. - We get an alpha release with TCM and Accord into users hands quickly for broader testing and feedback. - We isolate GA efforts on TCM and Accord – giving oss and downstream engineers time and patience reviewing and testing. TCM will be the biggest patch ever to land in C*. - Give users a choice for a more incremental upgrade approach, given just how many new features we're putting on them in one year. - 5.1 w/ TCM and Accord will maintain its upgrade compatibility with all 4.x versions, just as if it had landed in 5.0. The risks/costs this introduces are - If we cannot stabilise TCM and/or Accord on the cassandra-5.1 branch, and at some point decide to undo this work, while we can throw away the cassandra-5.1 branch we would need to do a bit of work reverting the changes in trunk. This is a _very_ edge case, as confidence levels on the design and implementation of both are already tested and high. - We will have to maintain an additional branch. I propose that we treat the 5.1 branch in the same maintenance window as 5.0 (like we have with 3.0 and 3.11). This also adds the merge path overhead. - Reviewing of TCM and Accord will continue to happen post-merge. This is not our normal practice, but this work will have already received its two +1s from committers, and such ongoing review effort is akin to GA stabilisation work on release branches. I see no other ok solution in front of us that gets us at least both the 5.0 beta and TCM+Accord alpha releases this year. Keeping in mind users demand to start experimenting with these features, and our Cassandra Summit in December. 1) https://lists.apache.org/thread/9c5cnn57c7oqw8wzo3zs0dkrm4f17lm3
