I was thinking about implementing this. I already have a ruby script that does it plus filters out idle unicorn stacks (yay for over-provisioned self-hosted infrastructure at work):

#!/usr/bin/ruby

require 'zlib'
require 'stringio'
require 'oj'

puts ARGV.inspect
Dir.chdir(ARGV[0])

def idling_unicorn?(line)
  json = Oj.load(line)
  return true unless json

  json = json['trace']

  json.dig(0, 'name') == '<c function>' &&
    json.dig(1, 'name') == 'worker_loop' &&
    json.dig(2, 'name') == 'spawn_missing_workers'
end

def each_trace(filename, &block)
  Zlib::GzipReader.open(filename) do |gz|
    enum = gz.each_line
    enum.take(1)
    enum.each(&block)
  end
end

def batch_process(batchsize)
  inputs = Dir['*.gz']
  inputs.delete('merged.gz')

  inputs.each_slice(batchsize) do |filenames|
    puts "Processing #{filenames}"

    tids = filenames.map do |filename|
      Thread.new do
        yield filename
      end
    end

    tids.each(&:join)
  end
end

`rm merged.gz` if Dir.exist?('merged.gz')

Zlib::GzipWriter.open('merged.gz') do |writer|
  writer.write("rbspy01\n")

  semaphore = Mutex.new

  batch_process(8) do |filename|
    data = []

    begin
      each_trace(filename) do |line|
        data << line unless idling_unicorn?(line)
      end
    rescue Zlib::GzipFile::Error => e
      puts "\n======\nError processing #{filename}: #{e.message}\n#{e.backtrace}"
      data = []
    end

    data = data.join('')

    semaphore.synchronize { writer.write(data) } unless data == ''
  end

  writer.close
end

Merging recorded stack traces #241

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