preload_perf

#!/usr/bin/env ruby

require_relative "../config/environment"

def rss_kb
  `ps -o rss= -p #{Process.pid}`.to_i
end

$measure_depth = 0

def measure(label)
  indent = "  " * $measure_depth
  GC.start
  rss_before = rss_kb
  objects_before = GC.stat(:total_allocated_objects)
  started_at = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  $measure_depth += 1
  yield
ensure
  $measure_depth -= 1
  time = Process.clock_gettime(Process::CLOCK_MONOTONIC) - started_at
  objects_after = GC.stat(:total_allocated_objects)
  rss_after = rss_kb

  puts format(
    "%-34s %8.2fms  rss %6dKB -> %6dKB (%+dKB)  objects +%d",
    indent + label, time * 1000, rss_before, rss_after, rss_after - rss_before,
    objects_after - objects_before
  )
end

t = Token.limit(5); t.load
t.preload(:meeting).load
t.preload(:meeting, :utterance).load

puts "=== Relation#preload (spawns a new relation, re-queries tokens each time) ==="
measure("total") do
  ActiveRecord::Base.cache do
    t = nil
    measure("Token.limit(5).load")           { t = Token.limit(5); t.load }
    measure("preload(:meeting)")             { t.preload(:meeting).load }
    measure("preload(:meeting, :utterance)") { t.preload(:meeting, :utterance).load }
    nil
  end
end

puts
puts "=== ActiveRecord::Associations::Preloader (preloads onto the same records) ==="
measure("total") do
  ActiveRecord::Base.cache do
    t = nil
    measure("Token.limit(5).load") { t = Token.limit(5).load }
    measure("Preloader(:meeting)") do
      ActiveRecord::Associations::Preloader.new(records: t, associations: :meeting).call
    end
    measure("Preloader(:meeting, :utterance)") do
      ActiveRecord::Associations::Preloader.new(records: t, associations: [ :meeting, :utterance ]).call
    end
    nil
  end
end