4.2 perf: AR new with serialized attrs up to 10x slower

[mfazekas]

We're seeing about +30% time increase in execution time, when running our rspec. (this is similiar to what reported at the end of #17472)
Profiling showed much more YAML parse(psych) compared to 4.1.

Given:

class DummyItem < ActiveRecord::Base
  serialize :data1, Array
  serialize :data2, Array
  serialize :data3, Array
  serialize :data4, Array

  after_initialize :init

  def init
    self.num = 42
  end
end

puts Benchmark.measure { 3000.times { DummyItem.new } }

is about 0.2 s in rails 4.1 vs 2.2 s in rails 4.2.rc3.

I don't think it affects web app performance much, but since we use factories and not fixtures for testing, the test execution speed suffers.

full testcase: https://gist.github.com/mfazekas/897f857e4367c94b771b

[mfazekas]

I have a quick WIP optimization: mfazekas@1800232
this seems to reduce time to about 0.5 s which is "only" 2.5x slower than rails 4.1 an 4x improvement from 4.2.rc3 for this usecase. This improves our rspec suite by about 10%.

[nateberkopec]

Just confirming using IPS instead:

# Rails 4.1.8
Calculating -------------------------------------
                         1.162k i/100ms
-------------------------------------------------
                         13.180k (± 5.3%) i/s -     66.234k
# Rails 4.2.0rc3
Calculating -------------------------------------
                       106.000  i/100ms
-------------------------------------------------
                          1.122k (± 9.1%) i/s -      5.618k

[nateberkopec]

Worth noting that the patch above doesn't do much for you if the serialized attr isn't nil. Modified test script here.

[sgrif]

Thanks for the report. The fix will be included in 4.2.1

[nateberkopec]

Thanks @sgrif!

[sgrif]

Also, using the benchmark provided, I'm seeing a significant speed-up on 4.2 after this change. 😁

master (which should reflect 4-2-stable's performance):

Calculating -------------------------------------
                         2.410k i/100ms
-------------------------------------------------
                         28.280k (± 1.6%) i/s -    142.190k

4.1:

Calculating -------------------------------------
                         1.889k i/100ms
-------------------------------------------------
                         21.745k (± 4.2%) i/s -    109.562k

[printercu]

👍 Thank you!

[mfazekas]

Thanks! Our rspec suite with 4.2.1pre now about 20% faster than with rails 4.1 (vs 4.2.0 was being 30% slower)

[sgrif]

❤️ !!!