raft topology: cdc: make CDC_GENERATIONS_V3 table single-partition, timeuuid-sorted #15163
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This was referenced Sep 7, 2023
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…uid-sorted' from Patryk Jędrzejczak We make the `CDC_GENERATIONS_V3` table single-partition and change the clustering key from `range_end` to `(id, range_end)`. We also change the type of `id` to `timeuuid` and ensure that a new generation always has the highest `id`. These changes allow efficient clearing of obsolete CDC generation data, which we need to prevent Raft-topology snapshots from endlessly growing as we introduce new generations over time. All this code is protected by an experimental feature flag. It includes the definition of `CDC_GENERATIONS_V3`. The table is not created unless the feature flag is enabled. Fixes #15163 Closes #15319 * github.com:scylladb/scylladb: system_keyspace: rename cdc_generation_id_v2 system_keyspace: change id to timeuuid in CDC_GENERATIONS_V3 cdc: generation: remove topology_description_generator cdc: do not create uuid in make_new_generation_data system_kayspace: make CDC_GENERATIONS_V3 single-partition cdc: generation: introduce get_common_cdc_generation_mutations cdc: generation: rename get_cdc_generation_mutations
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experimental raft topology, not backport needed |
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As discussed in #13962 (comment), we'll need a mechanism to clear obsolete CDC generation data so that raft-topology snapshot size does not grow endlessly as we introduce new generations over time.
The first step to do that is to turn the
system.cdc_generations_v3table into a single-partition table, where different generations are described through different clustering keys (as opposed by different partition keys, as it is today). Then turn generation IDs into timeuuids (currently they are just regular UUIDs), giving them a time-based order.Thanks to these changes, it will be easy to efficiently clear old generations -- e.g. by inserting a range tombstone covering all timeuuids < current_gen_timeuuid.
We should do this when while we can still change CDC_GENERATIONS_V3 table schema in backward incompatible ways (i.e. before we GA topology-on-raft).
cc @margdoc @gleb-cloudius
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