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e89b9799b8
Until now reversed queries were implemented inside `querier::consume_page` (more precisely, inside the free function `consume_page` used by `querier::consume_page`) by wrapping the passed-in reader into `make_reversing_reader` and then consuming fragments from the resulting reversed reader. The first couple of commits change that by pushing the reversing down below the `make_combined_reader` call in `table::query`. This allows working on improving reversing for memtables independently from reversing for sstables. We then extend the `index_reader` with functions that allow reading the promoted index in reverse. We introduce `partition_reversing_data_source`, which wraps an sstable data file and returns data buffers with contents of a single chosen partition as if the rows were stored in reverse order. We use the reversing source and the extended index reader in `mx_sstable_mutation_reader` to implement efficient (at least in theory) reversed single-partition reads. The patchset disables cache for reversed reads. Fast-forwarding is not supported in the mx reader for reversed queries at this point. Details in commit messages. Read the commits in topological order for best review experience. Refs: #9134 (not saying "Fixes" because it's only for single-partition queries without forwarding) Closes #9281 * github.com:scylladb/scylla: table: add option to automatically bypass cache for reversed queries test: reverse sstable reader with random schema and random mutations sstables: mx: implement reversed single-partition reads sstables: mx: introduce partition_reversing_data_source sstables: index_reader: add support for iterating over clustering ranges in reverse clustering_key_filter: clustering_key_filter_ranges owning constructor flat_mutation_reader: mention reversed schema in make_reversing_reader docstring clustering_key_filter: document clustering_key_filter_ranges::get_ranges