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0198d8e470
"This introduces an API which allows forward navigation in a stream of mutation fragments. It allows one to consume only a subset of the stream by iteratively specifying sub-ranges from which fragments should be returned. API outline: When in forwarding mode, the stream does not return all fragments right away, but only those belonging to the current range. Initially current range only covers the static row. The stream can be forwarded, even before reaching end- of-stream for current range, to a later range with fast_forward_to(). Forwarding doesn't change initial restrictions of the stream, it can only be used to skip over data. Monotonicity of positions is preserved by forwarding. That is fragments emitted after forwarding will have greater positions than any fragments emitted before forwarding. For any range, all range tombstones relevant for that range which are present in the original stream will be emitted. Range tombstones emitted before forwarding which overlap with the new range are not necessarily re-emitted. When not in forwarding mode, the stream acts as if the current range was equal to the full range. This implies that fast_forward_to() cannot be used. Whether stream is in forwarding mode or not is specified when the stream is created, typically via mutation_source interface. What's left for later series: Optimization by providing specialized implementations. This series implements forwarding support in all mutation sources via generic wrapper which simply drops fragments." * tag 'tgrabiec/clustering-fast-forward-to-v2' of github.com:scylladb/seastar-dev: tests: mutation_source_tests: Verify monotonicty of positions tests: random_mutation_generator: Spread the keys more tests: mutation_source_test: Make blobs more easily distinguishable tests: streamed_mutation: Test that merged stream passes mutation source tests tests: mutation_source_test: Add tests for forwarding of streamed_mutation tests: streamed_mutation_assertions: Add methods for navigating the stream tests: Add range generators to random_mutation_generator partition_slice_builder: Add with_ranges() query: Introduce full_clustering_range streamed_mutation: Add non-owning variant of mutation_from_streamed_mutation() db: Enable creating forwardable readers via mutation_source mutation_source: Document liveness requirements mutation_source: Cleanup db: Replace virtual_reader_type with mutation_source_opt partition_version: Refactor make_partition_snapshot_reader() overloads database: Fix mutation_source created by as_mutation_source() to not ignore trace_state_ptr memtable: Accept all mutation_source parameters streamed_mutation: Implement fast_forward_to() in stream merger streamed_mutation: Add generic implementation of forwardable streamed_mutation streamed_mutation: Add fast_forward_to() API position_in_partition: Introduce position_range position_in_partition: Introduce position constructor for right after the static row streamed_mutation: Make cast to view non-explicit streamed_mutation: Make schema() getter non-copying