Class: Datadog::Sampling::TokenBucket

Inherits:
RateLimiter show all
Defined in:
lib/ddtrace/sampling/rate_limiter.rb

Overview

Implementation of the Token Bucket metering algorithm for rate limiting.

See Also:

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(rate, max_tokens = rate) ⇒ TokenBucket

Returns a new instance of TokenBucket.

Parameters:

  • rate (Numeric) —

    Allowance rate, in units per second if rate is negative, always allow if rate is zero, never allow

  • max_tokens (Numeric) (defaults to: rate) —

    Limit of available tokens



34
35
36
37
38
39
40
41
42
 
# File 'lib/ddtrace/sampling/rate_limiter.rb', line 34

def initialize(rate, max_tokens = rate)
  @rate = rate
  @max_tokens = max_tokens

  @tokens = max_tokens
  @total_messages = 0
  @conforming_messages = 0
  @last_refill = Utils::Time.get_time
end

Instance Attribute Details

#max_tokens ⇒ Object (readonly)

Returns the value of attribute max_tokens.



28
29
30
 
# File 'lib/ddtrace/sampling/rate_limiter.rb', line 28

def max_tokens
  @max_tokens
end

#rate ⇒ Object (readonly)

Returns the value of attribute rate.



28
29
30
 
# File 'lib/ddtrace/sampling/rate_limiter.rb', line 28

def rate
  @rate
end

Instance Method Details

#allow?(size) ⇒ Boolean

Checks if a message of provided size conforms with the current bucket limit.

If it does, return true and remove size tokens from the bucket. If it does not, return false without affecting the tokens form the bucket.

Returns:

  • (Boolean) —

    true if message conforms with current bucket limit



53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
 
# File 'lib/ddtrace/sampling/rate_limiter.rb', line 53

def allow?(size)
  return false if @rate.zero?
  return true if @rate < 0

  refill_since_last_message

  increment_total_count

  return false if @tokens < size

  increment_conforming_count

  @tokens -= size

  true
end

#available_tokens ⇒ Numeric

Returns number of tokens currently available.

Returns:

  • (Numeric) —

    number of tokens currently available



84
85
86
 
# File 'lib/ddtrace/sampling/rate_limiter.rb', line 84

def available_tokens
  @tokens
end

#effective_rate ⇒ Float

Ratio of ‘conformance’ per ‘total messages’ checked on this bucket.

Returns 1.0 when no messages have been checked yet.

Returns:

  • (Float) —

    Conformance ratio, between [0,1]



76
77
78
79
80
81
 
# File 'lib/ddtrace/sampling/rate_limiter.rb', line 76

def effective_rate
  return 0.0 if @rate.zero?
  return 1.0 if @rate < 0 || @total_messages.zero?

  @conforming_messages.to_f / @total_messages
end