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When we build a materialized view we read the entire base table from start to end to generate all required view udpates. If a view is created while another view is being built on the same base table, this is optimized - we start generating view udpates for the new view from the base table rows that we're currently reading, and we read the missed initial range again after the previous view finishes building. The view building progress is only updated after generating view updates for some read partitions. However, there are scenarios where we'll generate no view updates for the entire read range. If this was not handled we could end up in an infinite view building loop like we did in https://github.com/scylladb/scylladb/issues/17293 To handle this, we mark the view as built if the reader generated no partitions. However, this is not always the correct conclusion. Another scenario where the reader won't encounter any partitions is when view building is interrupted, and then we perform a reshard. In this scenario, we set the reader for all shards to the last unbuilt token for an existing partition before the reshard. However, this partition may not exist on a shard after reshard, and if there are also no partitions with higher tokens, the reader will generate no partitions even though it hasn't finished view building. Additionally, we already have a check that prevents infinite view building loops without taking the partitions generated by the reader into account. At the end of stream, before looping back to the start, we advance current_key to the end of the built range and check for built views in that range. This handles the case where the entire range is empty - the conditions for a built view are: 1. the "next_token" is no greater than "first_token" (the view building process looped back, so we've built all tokens above "first_token") 2. the "current_token" is no less than "first_token" (after looping back, we've built all tokens below "first_token") If the range is empty, we'll pass these conditions on an empty range after advancing "current_key" to the end because: 1. after looping back, "next_token" will be set to `dht::minimum_token` 2. "current_key" will be set to `dht::ring_position::max()` In this patch we remove the check for partitions generated by the reader. This fixes the issue with resharding and it does not resurrect the issue with infinite view building that the check was introduced for. Fixes https://github.com/scylladb/scylladb/issues/26523 Closes scylladb/scylladb#26635