Module: Polyrun::Partition::Hrw

Defined in:
lib/polyrun/partition/hrw.rb

Overview

Rendezvous / highest-hash shard assignment (spec_queue.md): stateless, stable when m changes.

Class Method Summary collapse

Class Method Details

.score(path, shard_index, salt) ⇒ Object 



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# File 'lib/polyrun/partition/hrw.rb', line 28

def score(path, shard_index, salt)
  Digest::SHA256.digest("#{salt}\n#{path}\n#{shard_index}").unpack1("H*").hex
end

.shard_for(path:, total_shards:, seed: "") ⇒ Integer

Returns shard index in 0…m.

Returns:

  • (Integer) —

    shard index in 0…m

Raises:



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# File 'lib/polyrun/partition/hrw.rb', line 10

def shard_for(path:, total_shards:, seed: "")
  m = Integer(total_shards)
  raise Polyrun::Error, "total_shards must be >= 1" if m < 1

  best_j = 0
  best = -1
  salt = seed.to_s
  p = path.to_s
  m.times do |j|
    h = score(p, j, salt)
    if h > best
      best = h
      best_j = j
    end
  end
  best_j
end