"
After the recent conversion of the row-cache, two v1 mutation sources
remained: the memtable and the kl sstable reader.
This series converts both to a native v2 implementation. The conversion
is shallow: both continue to read and process the underlying (v1) data
in v1, the fragments are converted to v2 right before being pushed to
the reader's buffer. This conversion is simple, surgical and low-risk.
It is also better than the upgrade_to_v2() used previously.
Following this, the remaining v1 reader implementations are removed,
with the exception of the downgrade_to_v1(), which is the only one left
at this point. Removing this requires converting all mutation sinks to
accept a v2 stream.
upgrade_to_v2() is now not used in any production code. It is still
needed to properly test downgrade_to_v1() (which is till used), so we
can't remove it yet. Instead it hidden as a private method of
mutation_source. This still allows for the above mentioned testing to
continue, while preventing anyone from being tempted to introduce new
usage.
tests: https://jenkins.scylladb.com/job/releng/job/Scylla-CI/191
"
* 'convert-remaining-v1-mutation-sources/v2' of https://github.com/denesb/scylla:
readers: make upgrade_to_v2() private
test/lib/mutation_source_test: remove upgrade_to_v2 tests
readers: remove v1 forwardable reader
readers: remove v1 empty_reader
readers: remove v1 delegating_reader
sstables/kl: make reader impl v2 native
sstables/kl: return v2 reader from factory methods
sstables: move mp_row_consumer_reader_k_l to kl/reader.cc
partition_snapshot_reader: convert implementation to native v2
mutation_fragment_v2: range_tombstone_change: add minimal_memory_usage()
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