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When performing a schema change through group 0, extend the schema mutations with a version that's persisted and then used by the nodes in the cluster in place of the old schema digest, which becomes horribly slow as we perform more and more schema changes (#7620). If the change is a table create or alter, also extend the mutations with a version for this table to be used for `schema::version()`s instead of having each node calculate a hash which is susceptible to bugs (#13957). When performing a schema change in Raft RECOVERY mode we also extend schema mutations which forces nodes to revert to the old way of calculating schema versions when necessary. We can only introduce these extensions if all of the cluster understands them, so protect this code by a new cluster/schema feature, `GROUP0_SCHEMA_VERSIONING`. Fixes: #7620 Fixes: #13957 --- This is a reincarnation of PR scylladb/scylladb#15331. The previous PR was reverted due to a bug it unmasked; the bug has now been fixed (scylladb/scylladb#16139). Some refactors from the previous PR were already merged separately, so this one is a bit smaller. I have checked with @Lorak-mmk's reproducer (https://github.com/Lorak-mmk/udt_schema_change_reproducer -- many thanks for it!) that the originally exposed bug is no longer reproducing on this PR, and that it can still be reproduced if I revert the aforementioned fix on top of this PR. Closes scylladb/scylladb#16242 * github.com:scylladb/scylladb: docs: describe group 0 schema versioning in raft docs test: add test for group 0 schema versioning feature_service: enable `GROUP0_SCHEMA_VERSIONING` in Raft mode schema_tables: don't delete `version` cell from `scylla_tables` mutations from group 0 migration_manager: add `committed_by_group0` flag to `system.scylla_tables` mutations schema_tables: use schema version from group 0 if present migration_manager: store `group0_schema_version` in `scylla_local` during schema changes system_keyspace: make `get/set_scylla_local_param` public feature_service: add `GROUP0_SCHEMA_VERSIONING` feature