Ruby 2.1: Profiling Ruby

102 points by tmm1 12 years ago · 16 comments

Reader

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 12 years ago

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

sams99 12 years ago

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 12 years ago

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

MaulingMonkey 12 years ago
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
```
vs
```
  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 12 years ago
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 12 years ago
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 12 years ago
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 12 years ago
@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 12 years ago

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 12 years ago

Wait, what about stackprof rb-lineprof flamegraph rack-mini-profiler
Mithaldu 12 years ago

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 12 years ago

>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 12 years ago

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 12 years ago

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

Cool read!

Settings

Ruby 2.1: Profiling Ruby

Keyboard Shortcuts