Ruby 2.1: Profiling Ruby

102 pointstmm112 years ago15 comments

I wonder if this API allow will foster a big movement to track down all the performance-hungry calls in say, Rails, and help the framework move forward in terms of efficiency. This is really a welcome addition anyway.

akx 12y

I think TRWTF here is that checking for (query string?) parameter existence runs a regexp...

sams99 12y

Some of us like to pre-divine a world devoid of bugs and silliness, others like to provide us with tooling to track stuff down

wrl 12y

So, I'm a Ruby neophyte. Why did adding parenthesis speed that line up so much?

MaulingMonkey 12y

Rewritten in longer form, assuming I've made no mistakes, the two versions are equivalent to...

  if params[:user_id].present?
    if !@owner
      @owner = User.find_by_login(params[:user_id])
    end
  end

  if !@owner
    if params[:user_id].present?
      @owner = User.find_by_login(params[:user_id])
    end
  end

Checking the member variable truthiness is presumably faster than a dictionary lookup followed by a call to "present?". As @owner is probably frequently/always true after the first call (it will be unless find_by_login returns false/nil/? or another method resets @owner, given the same instance), this leads to fewer dictionary lookups and present? calls, resulting in a performance increase.

EDIT: Well that was an amusing spam of simultaneous answers.

Mithaldu 12y

I don't write Ruby, but it's close enough to Perl that i can tell you. Precedence is the reason.

The first line with more explicit precedence is this:

    if( params[:user_id].present?) {
        @owner ||= User.find_by_login(params[:user_id]) 
    }

The second line is this:

    @owner ||= (
        User.find_by_login(params[:user_id]) if params[:user_id].present?
    )

In other words, the first version always ran the present? method, while the second version only did so if @owner was false.

Moto7451 12y

I haven't done too much Ruby myself, but the line looks sufficiently Perl like I believe the subtle change converted the first line (rolled out) from:

(excusing my Perl-Ruby mashup)

  if (params[:user_id].present){
    if (!@owner){
      @owner = User.find_by_login(params[:user_id]);
    }
  }

to:

  if (!@owner){
    if (params[:user_id].present){
      @owner = User.find_by_login(params[:user_id]);
    }
  }

Now the call params[:user_id].present is only made if @owner lacks a value.

stock_toaster 12y

Assignment has higher precedence than if, so the line originally would have evaluated as:

  (@owner ||= User.find_by_login(params[:user_id])) if params[:user_id].present?

Thus always testing the if, and then conditionally setting @owner. The new line checks the existence of @owner before evaluating the if by using parens to set precedence.

jbverschoor 12y

@owner ||= User.find_by_login(params[:user_id]) if params[:user_id].present? means:

  if params[:user_id].present?
    if not @owner
      @owner = User.find_by_login(params[:user_id])
    end
  end

@owner ||= (User.find_by_login(params[:user_id]) if params[:user_id].present?) means:

  if not @owner
    if params[:user_id].present?
      @owner = User.find_by_login(params[:user_id])
    end
  end

So everytime someone called owner() to get the owner of a repo, the regex was checked

gazarsgo 12y

Why is line level profiling so non-existent for dynamic languages? Function level just doesn't cut it, esp. w/ the zillions of monkey patches in Ruby.

sams99 12y

Wait, what about stackprof rb-lineprof flamegraph rack-mini-profiler

Mithaldu 12y

My theory is that it takes both a certain amount of pressure to create those tools, a certain amount of expertise and a certain amount of tooling available from the language. Due to being old, Perl has all of these and in Devel::NYTProf has a more than excellent profiler that goes beyond line, into statement level. See for example these profiling runs created with it: https://dl.dropboxusercontent.com/u/10190786/ppi_bench.zip

copx 12y

Why is line level profiling so non-existent for dynamic languages?

It isn't. As usual the answer is LuaJIT (sorry, I am a fanboy, got to admit it): http://permalink.gmane.org/gmane.comp.lang.lua.luajit/3413

girvo 12y

I was just looking at phpdbg and xdebug yesterday, and they do it, iirc :) so, not impossible, but Ruby does do more stuff dynamically.

kbar13 12y

At first I didn't realize OP was a GitHub employee and thought he was munging his company's GHE appliance :o

Cool read!

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