Полное руководство по сбросам в кучу Ruby — часть 1

NOTE: Your output might differ; this library is young and will evolve over time (even as I’m writing this article).

This is a more useful information than the first command. We can see the most aggregate allocated memory occurred on line 9. This is also where we’ve allocated the largest number of objects:

a = "#{x}_foo"

It’s also useful to see what object retains the most other objects. In this case, an object is allocated on line 7 and contains references to 10,000 objects. It’s no surprise that this is our array:

ARRAY = []

The important thing to remember is that we record when the object was allocated, not when it was assigned. If I were looking at the script, I would ideally like a red flag on this line:

  ARRAY << a

However, there are no objects allocated on this line so it doesn’t show up in our heap dump. We have to infer that this is where the references are getting added by noting where objects are created and what lines reference large numbers of objects.

This means when we’re hunting for memory problems. Heap dumps are more of a tool for finding bread crumbs than smoking guns.

“Heap dumps are more of a tool for finding bread crumbs than smoking guns.” – via @schneems

Retained or Allocated or Both?

Ruby only includes the objects that have not been garbage collected in a heap dump. When you take a heap dump, you may get different results depending on if a garbage collection just ran or if it hasn’t run in a long time.

“Ruby only includes objects that have not been garbage collected in a heap dump.” – via @schneems

If you’re hunting for a memory leak, it won’t matter. You should be able to see allocated objects readily in your heap dumps since they haven’t been cleared.

However, if you’re looking for memory bloat, where lots of objects intermittently are created, you may get a heap dump right after they were cleared via a GC. To get a “clean” heap dump, you could manually force a GC by running GC.start before generating the heap dump. For example, if the script didn’t retain memory but simply created and discarded it:

require 'objspace'

ObjectSpace.trace_object_allocations_start

count = (ARGV.first || 5_000 ).to_i

def allocate_objects(count)
  array = []
  count.times do |x|
    a = "#{x}_foo"
    array << a
  end
  return nil
end

allocate_objects(count)

file_name = "/tmp/#{Time.now.to_f}-heap.dump"

file = File.open(file_name, 'w')

GC.start
ObjectSpace.dump_all(output: file)
file.close

puts "heapy read #{file_name}"

$ ruby scratch.rb 20_000
heapy read /tmp/1447433325.440035-heap.dump

Analyzing Heap
==============
Generation: nil object count: 7399
Generation:   5 object count: 1
Generation:   8 object count: 2
Generation:   9 object count: 2

$ ruby scratch.rb 20_000
heapy read /tmp/1447433430.98191-heap.dump

Analyzing Heap
==============
Generation: nil object count: 7399
Generation:   4 object count: 806
Generation:   5 object count: 10917
Generation:   6 object count: 5468
Generation:   7 object count: 1335
Generation:   8 object count: 1482

$ ruby /tmp/scratch 20_000

Analyzing Heap
==============
Generation: nil object count: 7395
Generation:   4 object count: 250
Generation:   5 object count: 11191
Generation:   6 object count: 5605
Generation:   7 object count: 1433
Generation:   8 object count: 1530