"
cache_flat_mutation_reader gets a native v2 implementation. The
underlying mutation representation is not changed: range deletions are
still stored as v1 range_tombstones in mutation_partition. These are
converted to range tombstone changes during reading.
This allows for separating the change of a native v2 reader
implementation and a native v2 in-memory storage format, enabling the
two to be done at separate times and incrementally.
This means there is still conversion ingoing when reading from cache and
when populating, but when reading from underlying, the stream can now be
passed through as-is without conversions.
Also, any future v2 related changes to the in-memory storage will now be
limited to the cache reader implementation itself.
In the process, the non-forwarding reader, whose only user is the cache,
is also converted to v2.
"
Performance results reported by Botond:
"
build/release/test/perf/perf_simple_query -c1 -m2G --flush --
duration=20
BEFORE
median 130421.76 tps ( 71.1 allocs/op, 12.1 tasks/op, 47462
insns/op)
median absolute deviation: 319.64
maximum: 131028.33
minimum: 127502.55
AFTER
median 133297.41 tps ( 64.1 allocs/op, 12.2 tasks/op, 45406
insns/op)
median absolute deviation: 2964.24
maximum: 137581.56
minimum: 123739.4
Getting rid of those upgrade/downgrade was good for allocs and ops.
Curiously there is a 0.1 rise in number of tasks though.
"
* 'row-cache-readers-v2/v1' of https://github.com/denesb/scylla:
row_cache: update reader implementations to v2
range_tombstone_change_generator: flush(): add end_of_range
readers/nonforwardable: convert to v2
read_context: fix indentation
read_context: coroutinize move_to_next_partition()
row_cache: cache_entry::read(): return v2 reader
row_cache: return v2 readers from make_reader*()
readers/delegating_v2: s/make_delegating_reader_v2/make_delegating_reader/
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