Category Archives: hosting

Errbit + HTTPS: Setting up Errbit reporter (Airbrake v5 gem) to work with self-signed HTTPS certificate

Note: If you’re using old Errbit version (0.2.0, 0.4.0) and an old Airbrake version (v4) please refer to this manual to make it work with self-signed certificates. Having an error catcher like Errbit behind SSL is generally a good idea. Especially when Errbit is hosted on a different server than you application (for example when […]

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Synology DMS 6 + Gitlab Docker + Gmail

When you’ll setup your Gitlab instance using Synology DMS 6.0 UI, despite the fact that you’ve provided all the Gmail credentials, you will notice that it does not send any emails. You probably end up with a message similar to this one when: EOFError: end of file reached It may sound a bit enigmatic, but […]

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Multiple UNIX sockets bindings for Puma cluster

If you want to bind Puma to a unix socket, you can do this either by providing a -b options: or using a puma.rb config file and setting the bind options. Unfortunately if you try to bind multiple Pumas to one socket, you might end up with issue similar to this one: So, what is […]

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Recovering QNAP NAS lost data when NAS not starting properly

QNAP is a company that designs great network attached storages (NAS). Unfortunately, even their NAS can crash. Mine did. Before you get to how to recover the lost data, here’s my NAS and RAID spec (so that you can understand what and why I did): QNAP TS-410U RAID5 4 HDD (/dev/sda, /dev/sdb, /dev/sdc, /dev/sdd) Approximately […]

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Ruby – Installation and compilation from sources on Debian

If you don’t want to use Ruby from your repositories and you don’t want (or can’t because of some reason) to use RVM, here’s a quick howto download and compile Ruby from sources (all the commands should be executed with sudo or as a super user): First a small update and some neccessery libs: Then […]

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MongoDB monitoring with Munin – Setting up Munin to work with MongoDB

To monitor MongoDB you can use many tools, some like MongoDB Management Service (MMS) are cloud based, some like Munin might be installed locally. Today we will focus on setting up Munin to monitor MongoDB. Getting started with Munin If you don’t know what Munin is, or how to install it on your platform, please […]

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Ruby & Rails: Making sure rake task won’t slow the site down

If you don’t have multiple cores and/or you have a small VPN, you may end up with a huge slow down of your web app, when rake tasks are executed. This can be a big issue especially when you use something like whenever to perform periodic tasks. Luckily there’s a nice program: nice is a […]

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Undefined and cache/xxx and invalid %-encoding weird requests

Recently I’ve been having a lot of weird looking requests that would end up reported in Errbit. Initially I thought that it is my fault but after double checking all the JS code, I would still get those errors. Fixing this is quite easy. Undefined/cache/xxx requests come from Complitly malware chrome plugin. Solution to this […]

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Nginx: Block access to certain parts of your app based on visitor country

It may be a good idea to enable some parts of your application based on a user country. You could do this on an application level: But why would you want to store non-business logic like this in your app? There’s a much better solution: you can use the Nginx GeoIP Module. To do […]

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Running GitLab 7.1 using Puma instead of a Unicorn

Warning Warning! Before you do this, please read why you should’nt: why did gitlab 6 switch back to unicorn? So now, when let’s get started… Gemfile updates Nothing special here. Just add: and then: Puma config Create a puma.rb file in your gitlab config dir and copy/paste this: and At this point, you should be […]

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One Danger of Freedom Patches

May 21, 2013

I posted a benchmark on twitter about comparing a DateTime with a string. This is a short blurrrggghhh post about the benchmark and why there is such a performance discrepancy.

Here is the benchmark:

require 'benchmark/ips'
require 'active_support/all' if ENV['AS']
require 'date'

now = DateTime.now

Benchmark.ips do |x|
  x.report("lhs") { now == "foo" }
  x.report("rhs") { "foo" == now }
end

First we’ll run the benchmark without Active Support, then we’ll run the benchmark with Active Support.

The Benchmarks

Without Active Support

[aaron@higgins rails (master)]$ bundle exec ruby argh.rb 
Calculating -------------------------------------
                 lhs     57389 i/100ms
                 rhs     76222 i/100ms
-------------------------------------------------
                 lhs  2020064.6 (±14.7%) i/s -    9870908 in   5.015172s
                 rhs  3066573.4 (±13.2%) i/s -   15091956 in   5.012879s
[aaron@higgins rails (master)]$

With Active Support

[aaron@higgins rails (master)]$ AS=1 bundle exec ruby argh.rb 
Calculating -------------------------------------
                 lhs      4786 i/100ms
                 rhs     26327 i/100ms
-------------------------------------------------
                 lhs    62858.4 (±23.6%) i/s -     296732 in   5.019005s
                 rhs  2866546.6 (±26.6%) i/s -   13031865 in   4.996482s
[aaron@higgins rails (master)]$

Numbers!

In the benchmarks without Active Support, the performance is fairly close. The standard deviation is pretty big, but the numbers are within the ballpark of each other.

In the benchmarks with Active Support, the difference is enormous. It’s not even close. Why is this?

What is the deal?

This speed difference is due to a Freedom Patch that Active Support applies to the DateTime class:

class DateTime
  # Layers additional behavior on DateTime#<=> so that Time and
  # ActiveSupport::TimeWithZone instances can be compared with a DateTime.
  def <=>(other)
    super other.to_datetime
  end
end

DateTime includes the Comparable module which will call the <=> method whenever you call the == method. This Freedom Patch calls to_datetime on whatever is on the right hand side of the comparison. Rails Monkey Patches the String class to add a to_datetime method, but “foo” is not a valid Date, so it raises an exception.

The Comparable module rescues any exception that happens inside <=> and returns false. This means that any time you call DateTime#== with something that doesn’t respond to to_datetime, an exception is raised and immediately thrown away.

The original implementation just does object equality comparisons, returns false, and it’s done. This is why the original implementation is so much faster than the implementation with the Freedom Patch.

My 2 Cents

These are the dangers of Freedom Patching. As a Rails Core member, I know this is a controversial opinion, but I am not a fan of Freedom Patching. It seems convienient until one day you wonder why is this code:

date == "foo"

so much slower than this code?

"foo" == date

Freedom Patching hides complexity behind a familiar syntax. It flips your world upside down; making code that seems reasonable do something unexpected. When it comes to code, I do not like the unexpected.

EDIT: I clarified the section about strings raising an exception. The actual exception occurrs in another monkeypatch in Rails.

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