Class: Sidekiq::Metrics::Histogram

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/sidekiq/metrics/shared.rb

Overview

Implements space-efficient but statistically useful histogram storage. A precise time histogram stores every time. Instead we break times into a set of known buckets and increment counts of the associated time bucket. Even if we call the histogram a million times, we’ll still only store 26 buckets. NB: needs to be thread-safe or resiliant to races.

To store this data, we use Redis’ BITFIELD command to store unsigned 16-bit counters per bucket per klass per minute. It’s unlikely that most people will be executing more than 1000 job/sec for a full minute of a specific type.

Constant Summary collapse

BUCKET_INTERVALS =

This number represents the maximum milliseconds for this bucket. 20 means all job executions up to 20ms, e.g. if a job takes 280ms, it’ll increment bucket. Note we can track job executions up to about 5.5 minutes. After that, it’s assumed you’re probably not too concerned with its performance.

[
  20, 30, 45, 65, 100,
  150, 225, 335, 500, 750,
  1100, 1700, 2500, 3800, 5750,
  8500, 13000, 20000, 30000, 45000,
  65000, 100000, 150000, 225000, 335000,
  1e20 # the "maybe your job is too long" bucket
].freeze
LABELS = 
[
  "20ms", "30ms", "45ms", "65ms", "100ms",
  "150ms", "225ms", "335ms", "500ms", "750ms",
  "1.1s", "1.7s", "2.5s", "3.8s", "5.75s",
  "8.5s", "13s", "20s", "30s", "45s",
  "65s", "100s", "150s", "225s", "335s",
  "Slow"
].freeze
FETCH = 
"GET u16 #0 GET u16 #1 GET u16 #2 GET u16 #3 \
GET u16 #4 GET u16 #5 GET u16 #6 GET u16 #7 \
GET u16 #8 GET u16 #9 GET u16 #10 GET u16 #11 \
GET u16 #12 GET u16 #13 GET u16 #14 GET u16 #15 \
GET u16 #16 GET u16 #17 GET u16 #18 GET u16 #19 \
GET u16 #20 GET u16 #21 GET u16 #22 GET u16 #23 \
GET u16 #24 GET u16 #25".split
HISTOGRAM_TTL = 
8 * 60 * 60

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(klass) ⇒ Histogram

Returns a new instance of Histogram.



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# File 'lib/sidekiq/metrics/shared.rb', line 60

def initialize(klass)
  @klass = klass
  @buckets = Array.new(BUCKET_INTERVALS.size) { Counter.new }
end

Instance Attribute Details

#buckets ⇒ Object (readonly)

Returns the value of attribute buckets.



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# File 'lib/sidekiq/metrics/shared.rb', line 59

def buckets
  @buckets
end

Instance Method Details

#each ⇒ Object 



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# File 'lib/sidekiq/metrics/shared.rb', line 51

def each
  buckets.each { |counter| yield counter.value }
end

#fetch(conn, now = Time.now) ⇒ Object 



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# File 'lib/sidekiq/metrics/shared.rb', line 73

def fetch(conn, now = Time.now)
  window = now.utc.strftime("%d-%H:%-M")
  key = "#{@klass}-#{window}"
  conn.bitfield_ro(key, *FETCH)
end

#label(idx) ⇒ Object 



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# File 'lib/sidekiq/metrics/shared.rb', line 55

def label(idx)
  LABELS[idx]
end

#persist(conn, now = Time.now) ⇒ Object 



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# File 'lib/sidekiq/metrics/shared.rb', line 79

def persist(conn, now = Time.now)
  buckets, @buckets = @buckets, []
  window = now.utc.strftime("%d-%H:%-M")
  key = "#{@klass}-#{window}"
  cmd = [key, "OVERFLOW", "SAT"]
  buckets.each_with_index do |counter, idx|
    val = counter.value
    cmd << "INCRBY" << "u16" << "##{idx}" << val.to_s if val > 0
  end

  conn.bitfield(*cmd) if cmd.size > 3
  conn.expire(key, HISTOGRAM_TTL)
  key
end

#record_time(ms) ⇒ Object 



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# File 'lib/sidekiq/metrics/shared.rb', line 65

def record_time(ms)
  index_to_use = BUCKET_INTERVALS.each_index do |idx|
    break idx if ms < BUCKET_INTERVALS[idx]
  end

  @buckets[index_to_use].increment
end