e145e758eb
When we create a CDC generation and ring-delay is non-zero, the timestamp of the new generation is in the future. Hence, we can have multiple generations that can be written to. However, if we add a new node to the cluster with the Raft-based topology, it receives only the last committed generation. So, this node will be rejecting writes considered correct by the other nodes until the last committed generation starts operating. In scylladb/scylladb#17134, we have allowed sending writes to the previous CDC generations. So, the situation became even more complicated. We need to adjust the Raft-based topology to ensure all required generations are loaded into memory and their data isn't cleared too early. This patch is the first step of the adjustment. We replace `current_cdc_generation_{uuid, timestamp}` with the set containing IDs of all committed generations - `committed_cdc_generations`. This set is sorted by timestamps, just like `unpublished_cdc_generations`. This patch is mostly refactoring. The last generation in `committed_cdc_generations` is the equivalent of the previous `current_cdc_generation_{uuid, timestamp}`. The other generations are irrelevant for now. They will be used in the following patches. After introducing `committed_cdc_generations`, a newly committed generation is also unpublished (it was current and unpublished before the patch). We introduce `add_new_committed_cdc_generation`, which updates both sets of generations so that we don't have to call `add_committed_cdc_generation` and `add_unpublished_cdc_generation` together. It's easy to forget that both of them are necessary. Before this patch, there was no call to `add_unpublished_cdc_generation` in `topology_coordinator::build_coordinator_state`. It was a bug reported in scylladb/scylladb#17288. This patch fixes it. This patch also removes "the current generation" notion from the Raft-based topology. For the Raft-based topology, the current generation was the last committed generation. However, for the `cdc::metadata`, it was the generation operating now. These two generations could be different, which was confusing. For the `cdc::metadata`, the current generation is relevant as it is handled differently, but for the Raft-based topology, it isn't. Therefore, we change only the Raft-based topology. The generation called "current" is called "the last committed" from now.
Scylla developer documentation
This folder contains developer-oriented documentation concerning the ScyllaDB codebase. We also have a wiki, which contains additional developer-oriented documentation. There is currently no clear definition of what goes where, so when looking for something be sure to check both.
Seastar documentation can be found here.
User documentation can be found on docs.scylladb.com
For information on how to build Scylla and how to contribute visit HACKING.md and CONTRIBUTING.md.