Bug #11461: Remove backtracing cleaning on Delegator methods

• Status: Closed
• Assignee: zzak (zzak _)
• Target version: -
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN

[rafaelfranca (Rafael França)]

This improve the performance in 18 times when the delegated method raises some exception and in 15% for the success case.

Here a benchmark result with a simpler script: (The backtrace have less than 10 items)

require 'delegate'
require 'benchmark/ips'

class Foo
  def name
    'foo'
  end

  def bla
    raise
  end
end

class Bar < DelegateClass(Foo)
end

bar = Bar.new(Foo.new)

Benchmark.ips do |b|
  b.report('default') { bar.name }
  b.report('default raising') { bar.bla rescue nil }
end

Before this patch:

$ ruby delegator_test.rb
Calculating -------------------------------------
             default    42.999k i/100ms
     default raising     1.456k i/100ms
-------------------------------------------------
             default      1.232M (± 9.9%) i/s -      6.106M
     default raising     14.399k (±13.6%) i/s -     71.344k

With this patch:

$ ruby delegator_test.rb
Calculating -------------------------------------
             default    49.024k i/100ms
     default raising    19.308k i/100ms
-------------------------------------------------
             default      1.484M (± 8.0%) i/s -      7.403M
     default raising    263.340k (± 8.0%) i/s -      1.313M

We could expect more performance difference in a huge application since their backtracers are bigger.

This changes the output of the exception from:

delegator_test.rb:18:in `bla': unhandled exception
    from delegator_test.rb:43:in `<main>'

To:

delegator_test.rb:18:in `bla': unhandled exception
    from /opt/ruby/lib/delegate.rb:340:in `block in delegating_block'
    from delegator_test.rb:43:in `<main>'

This patch is important because Rails 4.2 use Delegator in some critical paths.

From our production application this backtrace cleaner was one of the top 3 most CPU consuming calls. Here is the output of stackprof.

block (2 levels) in Delegator.delegating_block (/usr/lib/shopify-ruby/2.1.6-shopify2/lib/ruby/2.1.0/delegate.rb:345)
  samples:  1228 self (5.2%)  /   1228 total (5.2%)
  callers:
    1228  (  100.0%)  block in Delegator.delegating_block
  code:
 1228    (5.2%) /  1228   (5.2%)  |   345  |       $@.delete_if {|t| /\A#{Regexp.quote(__FILE__)}:#{__LINE__-2}:/o =~ t} if $@
                                  |   346  |     end

Given the positive performance impact and that the difference of the backtrace output is not so big, I believe it is worth to consider removing the backtrace cleaner.

[matz (Yukihiro Matsumoto)]

• Assignee changed from matz (Yukihiro Matsumoto) to zzak (zzak _)

OK, I accept.

Matz.

[zzak (zzak _)]

• Status changed from Open to Closed

Applied in changeset r51806.

---

• lib/delegate.rb: Remove backtrace cleaning for delegated methods
  This patch was provided by Rafael França and greatly improves
  performance when an exception is raised. [Bug #11461]

  Before:
  Calculating -------------------------------------
  default 86.209k i/100ms
  default raising 2.209k i/100ms

         default      1.953M (±11.0%) i/s -      9.655M
  

  default raising 21.826k (±13.5%) i/s - 108.241k

  After:
  Calculating -------------------------------------
  default 72.211k i/100ms
  default raising 34.288k i/100ms

         default      2.013M (±18.7%) i/s -      9.460M
  

  default raising 623.950k (± 9.7%) i/s - 3.120M

  Benchmark:
  require 'delegate'
  require 'benchmark/ips'

  class Foo
  def name
  'foo'
  end

  def bla
    raise
  end
  

  end

  class Bar < DelegateClass(Foo)
  end

  bar = Bar.new(Foo.new)

  Benchmark.ips do |b|
  b.report('default') { bar.name }
  b.report('default raising') { bar.bla rescue nil }
  end