Make AM Serializar at least three times faster

[SamSaffron]

While profiling Discourse with DTRACE I have notices a very large amount of time is being spent inside AM::Serializer iterating through hashes etc.

My fork is at: https://github.com/SamSaffron/active_model_serializers

I forked and patched it up so its AT LEAST twice faster ... and a lot more for larger serializer, results running against Ruby 2.0 are here (benchmark is in the benchmark folder)

                                             user     system      total        real
init                                     0.060000   0.000000   0.060000 (  0.061526)
fast_hash                                0.070000   0.000000   0.070000 (  0.066898)
fast_attributes                          0.260000   0.000000   0.260000 (  0.264070)
fast_serializable_hash                   0.350000   0.000000   0.350000 (  0.356954)
attributes                               0.470000   0.000000   0.470000 (  0.473984)
serializable_hash                        0.580000   0.000000   0.580000 (  0.573823)
serializable_hash_with_instrumentation   0.980000   0.000000   0.980000 (  0.983716)

The "fast_attributes" method is a direct drop in:

    def fast_attributes
      _fast_attributes
      rescue NameError
        method = "def _fast_attributes\n"

        method << "h = {}\n"

        INCLUDE_METHODS.each do |k,v|
          method << "h[:#{k}] = read_attribute_for_serialization(:#{k}) if #{v}\n"
        end
        method << "h\nend"

        self.class.class_eval method
        fast_attributes
    end

The other fix which has MAJOR perf benefits is stripping out the excessive instrumentation.

My recommendation here would be not to be doing any instrumentation in

def serializable_hash
      return nil if @object.nil?
      instrument(:serialize, :serializer => self.class.name) do
        @node = attributes
        instrument :associations do
          include_associations! if _embed
        end
        @node
      end
    end

If people would like instrumentation let them opt in with.

ActiveModel::Serializer.enable_instrumentation!

---

With both fixes in place real time goes down from 983ms to 356ms ... a pretty significant change.

---

Let me know if you are ok with both and I will turn this into a PR.

[SamSaffron]

Note, there is still room for improvement, the "if" checks can be omitted in the serializer generated if code is restructures a bit, also I think a method call can be erased. eg go directly to the object instead of bridging for certain cases.

[steveklabnik]

Please do send a pull. ❤️

On Mar 13, 2013, at 6:43 PM, Sam notifications@github.com wrote:

Note, there is still room for improvement, the "if" checks can be omitted in the serializer generated if code is restructures a bit, also I think a method call can be erased. eg go directly to the object instead of bridging for certain cases.

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