Currently we return proceed::no after every mutation_fragment which is
to be consumed. This froces parser to save and reload its state
often. This can be avoided if we pushed the fragments directly from
mp_row_consumer, then we would return proceed::no only when the buffer
fills up.
tests/perf/perf_fast_forward shows 15% increase in throughput of a large partition scan,
from 1.34M frag/s to 1.55M frag/s.
Message-Id: <1490882700-22684-1-git-send-email-tgrabiec@scylladb.com>