Module: NoBrainer::Document::PrimaryKey::Generator

Defined in:
lib/no_brainer/document/primary_key/generator.rb

Defined Under Namespace

Classes: Retry

Constant Summary collapse

BASE_TABLE = 
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz".freeze
TIME_OFFSET = 
Time.utc(2014, 01, 01).to_i
TIMESTAMP_BITS =

30 bits timestamp with 1s resolution -> We overflow in year 2048. Good enough. Math.log(Time.parse(‘2048-01-01’).to_f - TIME_OFFSET)/Math.log(2) = 29.999

30
SEQUENCE_BITS =

14 bits of sequence number. max 16k values per 1s slices. We want something >10k because we want to be able to do high speed inserts on a single process for future benchmarks.

14
MACHINE_ID_BITS =

24 bits of machine id 0.1% of chance to have a collision with 183 servers: Math.sqrt(-2*(2**24)*Math.log(0.999)) = 183.2 1% of chance to have a collision with ~580 servers. When using more than 500 machines, it’s therefore a good idea to set the machine_id manually to avoid collisions. XXX This is referenced in nobrainer/config.rb#default_machine_id

24
PID_BITS =

15 bits for the current pid. We wouldn’t need it if the sequence number was on a piece of shared memory :)

15
ID_STR_LENGTH =

Total: 83 bits With 14 digits in [A-Za-z0-9], we can represent 83 bits: Math.log(62**14)/Math.log(2) = 83.35

14
TIMESTAMP_MASK = 
(1 <<  TIMESTAMP_BITS)-1
SEQUENCE_MASK = 
(1 <<   SEQUENCE_BITS)-1
MACHINE_ID_MASK = 
(1 << MACHINE_ID_BITS)-1
PID_MASK = 
(1 <<        PID_BITS)-1
PID_SHIFT = 
0
MACHINE_ID_SHIFT = 
PID_SHIFT + PID_BITS
SEQUENCE_SHIFT = 
MACHINE_ID_SHIFT + MACHINE_ID_BITS
TIMESTAMP_SHIFT = 
SEQUENCE_SHIFT + SEQUENCE_BITS

Class Method Summary collapse

Class Method Details

._generate ⇒ Object 



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# File 'lib/no_brainer/document/primary_key/generator.rb', line 45

def self._generate
  timestamp = (Time.now.to_i - TIME_OFFSET) & TIMESTAMP_MASK

  unless @last_timestamp == timestamp
    # more noise is better in the ID, but we prefer to avoid
    # wrapping the sequences so that Model.last on a single
    # machine returns the latest created document.
    @first_sequence = sequence = rand(SEQUENCE_MASK/2)
    @last_timestamp = timestamp
  else
    sequence = (@sequence + 1) & SEQUENCE_MASK
    raise Retry if @first_sequence == sequence
  end
  @sequence = sequence

  machine_id = NoBrainer::Config.machine_id & MACHINE_ID_MASK

  pid = Process.pid & PID_MASK

  (timestamp << TIMESTAMP_SHIFT) | (sequence << SEQUENCE_SHIFT) |
    (machine_id << MACHINE_ID_SHIFT) | (pid << PID_SHIFT)
rescue Retry
  sleep 0.1
  retry
end

.convert_to_alphanum(id) ⇒ Object 



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# File 'lib/no_brainer/document/primary_key/generator.rb', line 71

def self.convert_to_alphanum(id)
  result = []
  until id.zero?
    id, r = id.divmod(BASE_TABLE.size)
    result << BASE_TABLE[r]
  end
  result.reverse.join.rjust(ID_STR_LENGTH, BASE_TABLE[0])
end

.field_type ⇒ Object 



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# File 'lib/no_brainer/document/primary_key/generator.rb', line 85

def self.field_type
  String
end

.generate ⇒ Object 



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# File 'lib/no_brainer/document/primary_key/generator.rb', line 81

def self.generate
  convert_to_alphanum(@lock.synchronize { _generate })
end