Graphite whisper file sizing calculator

graphite-calc.rb

#!/usr/bin/env ruby
# 
# eg: graphite-calc.rb  10s:10d,5m:400d,24h:20y 20
#     to calculate sizing for 20 hosts, 1000 metrics per host, 10s metric update interval
#

graphite_policy = ARGV.shift
num_hosts       = ARGV.shift || 1
num_metrics     = ARGV.shift || 1000
update_interval = ARGV.shift || 10

update_interval = Integer(update_interval)
num_metrics     = Integer(num_metrics)
num_hosts       = Integer(num_hosts)

policy_fragments = graphite_policy.split(/,/)

total_datapoints = 0
frag_datapoints = {}

def convert_to_seconds(time_spec)
  case time_spec
  when /^(\d+)$/
    return Integer($1)
  when /^(\d+)s$/
    return Integer($1)
  when /^(\d+)m$/
    return Integer($1) * 60
  when /^(\d+)h$/
    return Integer($1) * 60 * 60
  when /(\d+)d$/
    return Integer($1) * 60 * 60 * 24
  when /(\d+)y$/
    return Integer($1) * 60 * 60 * 24 * 365
  else
    raise "Bogus value '#{time_spec}'"
  end
end

policy_fragments.each do |frag|
  (precision, duration) = frag.split(/:/)

  precision_in_sec = convert_to_seconds(precision)
  duration_in_sec  = convert_to_seconds(duration)

  frag_datapoints[frag] = (duration_in_sec / precision_in_sec)
  total_datapoints += frag_datapoints[frag]

end

puts "Policy:             #{graphite_policy}"
puts "Send frequency (s): #{update_interval}"
puts "Number of metrics:  #{num_metrics}"
puts "Number of hosts:    #{num_hosts}"
puts
puts "Total Datapoints per metric: #{total_datapoints}"
puts "Per-fragment Datapoints:     #{frag_datapoints}"
puts "Size per metric:             #{total_datapoints * 12 / 1024}KiB"
puts
puts "Datapoints recd per second: #{ num_metrics * num_hosts / update_interval }"
puts "Total disk space needed:    #{ total_datapoints * 12 * num_hosts * num_metrics / ( 1024 * 1024 )}MiB"