storage_proxy has an optimization where it tries to query multiple token
ranges concurrently to satisfy very large requests (an optimization which is
likely meaningless when paging is enabled, as it always should be). However,
the rows-per-range code severely underestimates the number of rows per range,
resulting in a large number of "read-ahead" internal queries being performed,
the results of most of which are discarded.
Fix by disabling this code. We should likely remove it completely, but let's
start with a band-aid that can be backported.
Fixes#1863.
Message-Id: <20161120165741.2488-1-avi@scylladb.com>
(cherry picked from commit 6bdb8ba31d)
d9700a2826