From http://github.com/avikivity/scylla exponential-sharder/v3.
The sharder, which takes a range of tokens and splits it among shards, is
slow with large shard count and the default
murmur3_partitioner_ignore_msb_bits.
This patchset fixes excessive iteration in sstable sharding metadata writer and
nonsignular range scans.
Without this patchset, sealing a memtable takes > 60 ms on a 48-shard
system. With the patchset, it drops below the latency tracker threshold I
used (5 ms).
Fixes#2392.
(cherry picked from commit 84648f73ef)
e2c75d8532