Class: FFWD::Processor::HistogramProcessor

Inherits:
Object
  • Object
show all
Includes:
Logging, FFWD::Processor, Reporter
Defined in:
lib/ffwd/processor/histogram.rb

Overview

Implements histogram statistics over a tumbling time window.

Histogram received metrics continiuosly and regularly flushes out the following statistics.

<key>.min - Min value collected. <key>.max - Max value collected. <key>.mean - Mean value collected. <key>.p50 - The 50th percentile value collected. <key>.p75 - The 75th percentile value collected. <key>.p95 - The 95th percentile value collected. <key>.p99 - The 99th percentile value collected. <key>.p999 - The 99.9th percentile value collected.

Constant Summary collapse

DEFAULT_MISSING = 
0
DEFAULT_PERCENTILES = 
{
  :p50 => {:percentage => 0.50, :info => "50th"},
  :p75 => {:percentage => 0.75, :info => "75th"},
  :p95 => {:percentage => 0.95, :info => "95th"},
  :p99 => {:percentage => 0.99, :info => "99th"},
  :p999 => {:percentage => 0.999, :info => "99.9th"},
}

Instance Method Summary collapse

Methods included from Reporter

included, #increment, map_meta, #report!, #reporter_data

Methods included from Logging

included, #log

Methods included from FFWD::Processor

category, included, load_discovered, load_processors, #name, registry

Methods included from Lifecycle

#depend_on, #start, #started?, #starting, #starting_hooks, #stop, #stopped?, #stopping, #stopping_hooks

Constructor Details

#initialize(emitter, opts = {}) ⇒ HistogramProcessor

Options:

:window - Define at what period the cache is flushed and generates metrics. :cache_limit - Limit the amount of cache entries (by key). :bucket_limit - Limit the amount of limits for each cache entry. :precision - Precision of emitted metrics. :percentiles - Configuration hash of percentile metrics. Structure:

{:p10 => {:info => "Some description", :percentage => 0.1}, ...}



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# File 'lib/ffwd/processor/histogram.rb', line 70

def initialize emitter, opts={}
  @emitter = emitter

  @window = opts[:window] || 10
  @cache_limit = opts[:cache_limit] || 1000
  @bucket_limit = opts[:bucket_limit] || 10000
  @precision = opts[:precision] || 3
  @missing = opts[:missing] || DEFAULT_MISSING
  @percentiles = opts[:percentiles] || DEFAULT_PERCENTILES

  # Dropped values that would have gone into a bucket.
  @cache = {}

  starting do
    log.info "Starting histogram processor on a window of #{@window}s"
  end

  stopping do
    log.info "Stopping histogram processor"
    @timer.cancel if @timer
    @timer = nil
    digest!
  end
end

Instance Method Details

#calculate(bucket) {|"max", "Max", max| ... } ⇒ Object

Yields:

  • ("max", "Max", max) 


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# File 'lib/ffwd/processor/histogram.rb', line 127

def calculate bucket
  total = bucket.size

  map = {}

  @percentiles.each do |k, v|
    index = (total * v[:percentage]).ceil - 1

    if (c = map[index]).nil?
      info = "#{v[:info]} percentile"
      c = map[index] = {:info => info, :values => []}
    end

    c[:values] << {:name => k, :value => nil}
  end

  max = nil
  min = nil
  sum = 0.0
  mean = nil

  bucket.sort.each_with_index do |t, index|
    max = t if max.nil? or t > max
    min = t if min.nil? or t < min
    sum += t

    unless (c = map[index]).nil?
      c[:values].each{|d| d[:value] = t}
    end
  end

  mean = sum / total

  unless @precision.nil?
    max = max.round(@precision)
    min = min.round(@precision)
    sum = sum.round(@precision)
    mean = mean.round(@precision)

    map.each do |index, c|
      c[:values].each{|d| d[:value] = d[:value].round(@precision)}
    end
  end

  yield "max", "Max", max
  yield "min", "Min", min
  yield "sum", "Sum", sum
  yield "mean", "Mean", mean

  map.each do |index, c|
    c[:values].each do |d|
      yield d[:name], c[:info], d[:value]
    end
  end
end

#check_timer ⇒ Object 



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# File 'lib/ffwd/processor/histogram.rb', line 95

def check_timer
  return if @timer

  log.debug "Starting timer"

  @timer = EM::Timer.new(@window) do
    @timer = nil
    digest!
  end
end

#digest! ⇒ Object

Digest the cache.



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# File 'lib/ffwd/processor/histogram.rb', line 107

def digest!
  if @cache.empty?
    return
  end

  ms = FFWD.timing do
    @cache.each do |key, bucket|
      calculate(bucket) do |p, info, value|
        @emitter.metric.emit(
          :key => "#{key}.#{p}", :source => key,
          :value => value, :description => "#{info} of #{key}")
      end
    end

    @cache = {}
  end

  log.debug "Digest took #{ms}ms"
end

#process(m) ⇒ Object 



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# File 'lib/ffwd/processor/histogram.rb', line 183

def process m
  key = m[:key]
  value = m[:value] || @missing

  if (bucket = @cache[key]).nil?
    return increment :dropped if @cache.size >= @cache_limit
    @cache[key] = bucket = []
  end

  return increment :bucket_dropped if bucket.size >= @bucket_limit
  return increment :dropped if stopped?
  increment :received

  bucket << value
  check_timer
end