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=== Introduction === This feature extends the nodetool refresh to allow loading arbitrary sstables that do not belong to a node into the cluster. It loads the sstables from disk and calculates the owning nodes of the data and streams to the owners automatically. From example, say the old cluster has 6 nodes and the new cluster has 3 nodes. We can copy the sstables from the old cluster to any of the new nodes and trigger the load and stream process. This can make restores and migrations much easier. === Performance === I managed to get 40MB/s per shard on my build machine. CPU: AMD Ryzen 7 1800X Eight-Core Processor DISK: Samsung SSD 970 PRO 512GB Assume 1TB sstables per node, each shard can do 40MB/s, each node has 32 shards, we can finish the load and stream 1TB of data in 13 mins on each node. 1TB / 40 MB per shard * 32 shard / 60 s = 13 mins === Tests === backup_restore_tests.py:TestBackupRestore.load_and_stream_to_new_cluster_test which creates a cluster with 4 nodes and inserts data, then use load_and_stream to restore to a 2 nodes cluster. === Usage === curl -X POST "http://{ip}:10000/storage_service/sstables/{keyspace}?cf={table}&load_and_stream=true === Notes === Btw, with the old nodetool refresh, the node will not pick up the data that does not belong to this node but it will not delete it either. One has to run nodetool cleanup to remove those data manually which is a surprise to me and probably to users as well. With load and stream, the process will delete the sstables once it finishes stream, so no nodetool cleanup is needed. The name of this feature load and stream follows load and store in CPU world. Fixes #7831