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With this change, you can add or remove a DC(s) in a single ALTER KEYSPACE statement. It requires the keyspace to use rack list replication factor. In existing approach, during RF change all tablet replicas are rebuilt at once. This isn't the case now. In global_topology_request::keyspace_rf_change the request is added to a ongoing_rf_changes - a new column in system.topology table. In a new column in system_schema.keyspaces - next_replication - we keep the target RF. In make_rf_change_plan, load balancer schedules necessary migrations, considering the load of nodes and other pending tablet transitions. Requests from ongoing_rf_changes are processed concurrently, independently from one another. In each request racks are processed concurrently. No tablet replica will be removed until all required replicas are added. While adding replicas to each rack we always start with base tables and won't proceed with views until they are done (while removing - the other way around). The intermediary steps aren't reflected in schema. When the Rf change is finished: - in system_schema.keyspaces: - next_replication is cleared; - new keyspace properties are saved; - request is removed from ongoing_rf_changes; - the request is marked as done in system.topology_requests. Until the request is done, DESCRIBE KEYSPACE shows the replication_v2. If a request hasn't started to remove replicas, it can be aborted using task manager. system.topology_requests::error is set (but the request isn't marked as done) and next_replication = replication_v2. This will be interpreted by load balancer, that will start the rollback of the request. After the rollback is done, we set the relevant system.topology_requests entry as done (failed), clear the request id from system.topology::ongoing_rf_changes, and remove next_replication. Fixes: SCYLLADB-567. No backport needed; new feature. Closes scylladb/scylladb#24421 * github.com:scylladb/scylladb: service: fix indentation docs: update documentation test: test multi RF changes service: tasks: allow aborting ongoing RF changes cql3: allow changing RF by more than one when adding or removing a DC service: handle multi_rf_change service: implement make_rf_change_plan service: add keyspace_rf_change_plan to migration_plan service: extend tablet_migration_info to handle rebuilds service: split update_node_load_on_migration service: rearrange keyspace_rf_change handler db: add columns to system_schema.keyspaces db: service: add ongoing_rf_changes to system.topology gms: add keyspace_multi_rf_change feature
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.