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dac93b2096
This change makes tablet load balancing more efficient by performing migrations independently for different tablets, and making new load balancing plans concurrently with active migrations. The migration track is interrupted by pending topology change operations. The coordinator executes the load balancer on edges of tablet state machine transitions. This allows new migrations to be started as soon as tablets finish streaming. The load balancer is also continuously invoked as long as it produces a non-empty plan. This is in order to saturate the cluster with streaming. A single make_plan() call is still not saturating, due to the way algorithm is implemented. Overload of shards is limited by the fact that load balancer algorithm tracks streaming concurrency on both source and target shards of active migrations and takes concurrency limit into account when producing new migrations. Closes #14851 * github.com:scylladb/scylladb: tablets: load_balancer: Remove double logging tests: tablets: Check that load balancing is interrupted by topology change tests: tablets: Add test for load balancing with active migrations tablets: Balance tablets concurrently with active migrations storage_service, tablets: Extract generate_migration_updates() storage_service, tablets: Move get_leaving_replica() to tablets.cc locator: tablets: Move std::hash definition earlier storage_service: Advance tablets independently topology_coordinator: Fix missed notification on abort tablets: Add formatter for tablet_migration_info