This config item controls how many CPU-bound reads are allowed to run in
parallel. The effective concurrency of a single CPU core is 1, so
allowing more than one CPU-bound reads to run concurrently will just
result in time-sharing and both reads having higher latency.
However, restricting concurrency to 1 means that a CPU bound read that
takes a lot of time to complete can block other quick reads while it is
running. Increase this default setting to 2 as a compromise between not
over-using time-sharing, while not allowing such slow reads to block the
queue behind them.
Fixes: #22450Closesscylladb/scylladb#22679
(cherry picked from commit 3d12451d1f)
Closesscylladb/scylladb#22722
ff7e93ddd5