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7d9ab44e81
When new nodes are added or existing nodes are deleted, the topology state machine needs to shunt reads from the old nodes to the new ones. This happens in the `write_both_read_new` state. The problem is that previously this state was not handled in any way in `token_metadata` and the read nodes were only changed when the topology state machine reached the final 'owned' state. To handle `write_both_read_new` an additional `interval_map` inside `token_metadata` is maintained similar to `pending_endpoints`. It maps the ranges affected by the ongoing topology change operation to replicas which should be used for reading. When topology state sm reaches the point when it needs to switch reads to a new topology, it passes `request_read_new=true` in a call to `update_pending_ranges`. This forces `update_pending_ranges` to compute the ranges based on new topology and store them to the `interval_map`. On the data plane, when a read on coordinator needs to decide which endpoints to use, it first consults this `interval_map` in `token_metadata`, and only if it doesn't contain a range for current token it uses normal endpoints from `effective_replication_map`. Closes #13376 * github.com:scylladb/scylladb: storage_proxy, storage_service: use new read endpoints storage_proxy: rename get_live_sorted_endpoints->get_endpoints_for_reading token_metadata: add unit test for endpoints_for_reading token_metadata: add endpoints for reading sequenced_set: add extract_set method token_metadata_impl: extract maybe_migration_endpoints helper function token_metadata_impl: introduce migration_info token_metadata_impl: refactor update_pending_ranges token_metadata: add unit tests token_metadata: fix indentation token_metadata_impl: return unique_ptr from clone functions