libring-balance-issue.md

There's something out of whack with the consistent hash algorithm used by swarm (libring):

Add 4 nodes all weighted equally (should be 4 x 25%) libring

iex> ring = HashRing.new()
iex> ring = HashRing.add_node(ring, :a@nohost)
iex> ring = HashRing.add_node(ring, :b@nohost)
iex> ring = HashRing.add_node(ring, :c@nohost)
iex> ring = HashRing.add_node(ring, :d@nohost)
iex> HashRing.balance_check(ring, 1000000)
{:ok, {1000000, 280936000, 280.936},
 [{:a@nohost, 268608, 0.268608}, {:b@nohost, 295090, 0.29509},
  {:c@nohost, 221535, 0.221535}, {:d@nohost, 214767, 0.214767}]}

Node	Expected	Actual	Error
:a@nohost	25%	26.86%	+7.44%
:b@nohost	25%	29.51%	+18.04%
:c@nohost	25%	22.15%	-11.39%
:d@nohost	25%	21.48%	-14.09%

Add 4 nodes all weighted equally (should be 4 x 25%) ryng

iex> {:ok, _} = :ryng.new_ring([id: :test])
iex> :ryng.add_node(:test, :a@nohost)
iex> :ryng.add_node(:test, :b@nohost)
iex> :ryng.add_node(:test, :c@nohost)
iex> :ryng.add_node(:test, :d@nohost)
iex> :ryng.balance_check(:test, 1000000)
{:ok, {1000000, 1317824000, 1317.824},
 [{:a@nohost, 249886, 0.249886}, {:b@nohost, 250168, 0.250168},
  {:c@nohost, 250055, 0.250055}, {:d@nohost, 249891, 0.249891}]}

Node	Expected	Actual	Error
:a@nohost	25%	24.99%	-0.05%
:b@nohost	25%	25.02%	+0.07%
:c@nohost	25%	25.01%	-0.02%
:d@nohost	25%	24.99%	-0.04%