discourse/script/memory-analysis

#!/usr/bin/env ruby
# frozen_string_literal: true

require 'fileutils'
require 'pathname'
require 'tmpdir'
require 'json'

def usage
  STDERR.puts "Usage: memory-analysis [PID|DUMPFILE]"
  exit 1
end

if ARGV.length != 1
  usage
end

dumpfile = ARGV[0]

if !File.exist?(dumpfile)
  pid = dumpfile.to_i
  usage if pid == 0

  time = Time.now.utc
  utc = time.strftime("%Y-%m-%d-%H-%M-%S")
  dumpfile = "#{Pathname.new(Dir.tmpdir).realpath}/#{pid}_#{utc}.dump"

  puts "Dumping heap for pid #{pid} to #{dumpfile}"
  puts

  `rbtrace -p #{pid} -e 'Thread.new{GC.start;require "objspace";io=File.open("#{dumpfile}", "w"); ObjectSpace.dump_all(output: io); io.close}'`

  old_size = 0

  found = false
  20.times do
    sleep 0.2
    found = File.exist?(dumpfile)
    break if found
  end

  if !found
    STDERR.puts "Unable to find dumpfile #{dumpfile}, is rbtrace running properly, did you pick the right pid?"
    usage
  end

  while true
    sleep 0.5
    size = File.size(dumpfile)
    if size == old_size && size > 0
      break
    end
    old_size = size
  end
end

puts "Processing heap dump"

class Stats

  def initialize
    @classes = {}
    @class_stats = {}
    @type_stats = {}
    @threads = Set.new
    @thread_owners = {}
  end

  def print
    puts "Stats by Type"
    puts "-" * 20
    puts

    @type_stats.sort_by { |_, (_, size)| -size }.each do |k, (count, size)|
      puts "#{k} Count: #{count} Size: #{size}"
    end
    puts

    puts "Stats by Class"
    puts "-" * 20
    @class_stats.sort_by { |_, (_, size)| -size }.each do |k, (count, size)|
      puts "#{@classes[k] || k} Count: #{count} Size: #{size}"
    end

    puts "Thread Stats"
    puts "-" * 20
    @thread_owners.sort_by { |_ , count| -count }.each do |name, count|
      puts "#{count} refs from #{name}"
    end
  end

  def thread_class
    @thread_class ||=
      begin
        @classes.find do |addr, n|
          n == "Thread"
        end.first
      end
  end

  def detect_threads(line)
    parsed = JSON.parse(line)

    if parsed["class"] == thread_class
      @threads << parsed["address"]
    end
  end

  def detect_thread_owners(line)
    parsed = JSON.parse(line)

    if refs = parsed["references"]
      i = 0
      while i < refs.length
        if @threads.include?(refs[i])
          klass = @classes[parsed["class"]] || "#{parsed["type"]} #{parsed["address"]}"
          @thread_owners[klass] ||= 0
          @thread_owners[klass] += 1
        end
        i += 1
      end
    end
  end

  def injest(line)
    parsed = JSON.parse(line)
    if parsed["type"] == "CLASS"
      @classes[parsed["address"]] = parsed["name"]
    end

    type_stat = @type_stats[parsed["type"]] ||= [0, 0]

    if klass = parsed["class"]
      class_stat = @class_stats[parsed["class"]] ||= [0, 0]
      class_stat[0] += 1
      class_stat[1] += parsed["memsize"] || 0
    end

    type_stat[0] += 1
    type_stat[1] += parsed["memsize"] || 0
  end
end

def process_dumpfile(dumpfile)
  stats = Stats.new

  File.open(dumpfile).each_line do |line|
    stats.injest(line)
  end

  puts "pass 1 done"

  File.open(dumpfile).each_line do |line|
    stats.detect_threads(line)
  end

  puts "pass 2 done"

  File.open(dumpfile).each_line do |line|
    stats.detect_thread_owners(line)
  end

  stats
end

stats = process_dumpfile(dumpfile)

stats.print