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
e89b9799b8