And use a temporary vector to use the precalculated distances.
A later patch will add some randomization to shuffle nodes
at the same distance from the reference node.
This improves the function performance by 50% for 3 replicas,
from 77.4 ns to 39.2 ns, larger replica sets show greater improvement
(over 4X for 15 nodes):
Before:
test iterations median mad min max allocs tasks inst cycles
sort_by_proximity_topology.perf_sort_by_proximity 12808773 77.368ns 0.062ns 77.300ns 77.873ns 0.000 0.000 1194.2 231.6
After:
sort_by_proximity_topology.perf_sort_by_proximity 25541973 39.225ns 0.114ns 38.966ns 39.339ns 0.000 0.000 588.5 116.6
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
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