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10bf8c7901
We plan to move pending_endpoints and read_endpoints, along with their computation logic, from token_metadata to vnode_effective_replication_map. The vnode_effective_replication_map seems more appropriate for them since it contains functionally similar _replication_map and we will be able to reuse pending_endpoints/read_endpoints across keyspaces sharing the same factory_key. At present, pending_endpoints and read_endpoints are updated in the update_pending_ranges function. The update logic comprises two parts - preparing data common to all keyspaces/replication_strategies, and calculating the migration_info for specific keyspaces. In this commit, we introduce a new topology_change_info structure to hold the first part's data add create an update_topology_change_info function to update it. This structure will later be used in vnode_effective_replication_map to compute pending_endpoints and read_endpoints. This enables the reuse of topology_change_info across all keyspaces, unlike the current update_pending_ranges implementation, which is another benefit of this refactoring. The update_topology_change_info implementation is mostly derived from update_pending_ranges, there are a few differences though: * replacing async and thread with plain co_awaits; * adding a utils::clear_gently call for the previous value to mitigate reactor stalls if target_token_metadata grows large; * substituting immediately invoked lambdas with simple variables and blocks to reduce noise, as lambdas would need to be converted into coroutines. The original update_pending_ranges remains unchanged, and will be removed entirely upon transitioning to the new implementation. Meanwhile, we add an update_topology_change_info call to storage_service::update_pending_ranges so that we can iteratively switch the system to the new implementation.