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d9b8278178
During an ALTER KEYSPACE statement execution where a table with a view is present, we need to perform tablet migrations for both tables. These migrations are not synchronized, so at some point the base may have a different number of non-pending replicas than the view. Because of that, we can't pair them correctly. If there is more non-pending base replicas than view replicas, we don't need to do anything because the view replica that didn't finish migrating is a pending replica and will get view updates from all base replicas. But if there is more non-pending view replicas than base replicas, we may currently lose view updates to the new view replica. This patch adds a workaround for this scenario. If after one migration we have too more non-pending view replicas than base replicas, we add it to the pending replica list so that it gets an update anyway. This patch will also take effect if the base and view replica counts differ due to some other bug. To track that, a new metric is added to count such occurrences. This patch also includes a test for this exact scenario, which is enforced by an injection. Fixes https://github.com/scylladb/scylladb/issues/21492