NewReplicaPlacementFromByte formatted the byte with fmt.Sprintf and parsed the
result back, allocating a string and a ReplicaPlacement every call. The master
calls it once per volume in every heartbeat, and keeps the pointer for the
lifetime of the volume, so a cluster with 1.6M volume replicas carries 1.6M of
these where a handful of distinct values exist.
The table is a flat pointer-free array, so it costs 6KB of static data and no
heap objects however few placements a cluster actually uses.
A byte only ever decodes to a valid placement, so the table is complete and the
error return stays nil.
BenchmarkSyncDataNodeRegistration/100000Volumes 500601 allocs/op -> 300589 allocs/op
Chris Lu