Class: ActiveRecord::Turntable::Algorithm::HashSlotAlgorithm

Inherits:
Base
  • Object
show all
Defined in:
lib/active_record/turntable/algorithm/hash_slot_algorithm.rb

Constant Summary collapse

DEFAULT_HASH_FUNC = 
->(key) { Zlib.crc32(key.to_s) }

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(config = {}) ⇒ HashSlotAlgorithm

Returns a new instance of HashSlotAlgorithm.



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# File 'lib/active_record/turntable/algorithm/hash_slot_algorithm.rb', line 9

def initialize(config = {})
  super
  @hash_func = @config[:hash_func] || DEFAULT_HASH_FUNC
end

Instance Attribute Details

#hash_func ⇒ Object (readonly)

Returns the value of attribute hash_func.



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# File 'lib/active_record/turntable/algorithm/hash_slot_algorithm.rb', line 7

def hash_func
  @hash_func
end

Instance Method Details

#choose(shard_maps, key) ⇒ Object

Raises:



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# File 'lib/active_record/turntable/algorithm/hash_slot_algorithm.rb', line 14

def choose(shard_maps, key)
  slot = slot_for_key(key, shard_maps.last.range.max)
  shard_map = shard_maps.bsearch { |shard| slot <= shard.range.max }
  raise ActiveRecord::Turntable::CannotSpecifyShardError, "cannot specify shard for key:#{key}" unless shard_map
  shard_map.shard
end

#choose_index(shard_maps, key) ⇒ Object 



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# File 'lib/active_record/turntable/algorithm/hash_slot_algorithm.rb', line 21

def choose_index(shard_maps, key)
  slot = slot_for_key(key, shard_maps.last.range.max)
  (0...shard_maps.size).bsearch { |idx| slot <= shard_maps[idx].range.max } or
    raise ActiveRecord::Turntable::CannotSpecifyShardError, "cannot specify shard for key:#{key}"
end

#shard_weights(shard_maps, current_sequence_value) ⇒ Object 



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# File 'lib/active_record/turntable/algorithm/hash_slot_algorithm.rb', line 31

def shard_weights(shard_maps, current_sequence_value)
  shard_maps.map { |shard_map| [shard_map.shard, shard_map.range.size] }.to_h
end

#slot_for_key(key, max) ⇒ Object 



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# File 'lib/active_record/turntable/algorithm/hash_slot_algorithm.rb', line 27

def slot_for_key(key, max)
  hash_func.call(key) % (max + 1)
end