Harris Novick lightyrs

Running statistics with Redis and Lua

This is an example for computing running statistics with Lua backed by a hash in Redis. We support counting, average (with and without exponential smoothing), stddev, variance, min, max, sum of observed values. An example for approximating a running median can be found here: https://gist.github.com/thomasdarimont/fff68191d45a001b2d84

Data structure

We use a hash for storing various statistic value under the key "stats_value" in redis. Note: If you need a specific alpha value for smoothing the average, then set the desired alpha -> e.g. alpha 0.7. If alpha is 0.0 then no smoothing is applied.

My largest Sidekiq application had a memory leak and I was able to find and fix it in just few hours spent on analyzing Ruby's heap. In this post I'll show my profiling setup.

As you might know Ruby 2.1 introduced a few great changes to ObjectSpace, so now it's much easier to find a line of code that is allocating too many objects. Here is great post explaining how it's working.

I was too lazy to set up some seeding and run it locally, so I checked that test suite passes when profiling is enabled and pushed debugging to production. Production environment also suited me better since my jobs data can't be fully random generated.

So, in order to profile your worker, add this to your Sidekiq configuration:

if ENV["PROFILE"]

One of the many reasons I love working with Ruby is it has a rich vocabulary that allows you to accomplish your goals with a minimal amount of code. If there isn't a method that does exactly what you want, it's usually possible to build an elegant solution yourself.

Let's take the example of simulating the rolling of a die.

We can represent a die as an array of its faces.

die = [*?⚀..?⚅]
# => ["⚀", "⚁", "⚂", "⚃", "⚄", "⚅"]

Setup

Replace IRB with Pry (in your Gemfile) and Byebug with pry-byebug.

gem 'pry-rails', group: [:development, :test]
gem 'pry-byebug', group: [:development, :test]

Using PRY

Combining ActiveRecord Scopes with `OR` [<v5]

This came about while trying to construct an ActiveRecord query.

via http://stackoverflow.com/a/9540911/111363

Note that merge combines WHERE clauses using AND. While ActiveRecord does not currently have the ability to combine relations using OR instead, it is coming in ActiveRecord 5 (https://github.com/rails/rails/commit/9e42cf019f2417473e7dcbfcb885709fa2709f89).

It'll look something like this:

via http://tombroomfield.com/the-upcoming-active-record-or-method-will-clean-up-your-queries/

	# lib/tasks/db.rake
	namespace :db do

	desc "Dumps the database to db/APP_NAME.dump"
	task :dump => :environment do
	cmd = nil
	with_config do \|app, host, db, user\|
	cmd = "pg_dump --host #{host} --username #{user} --verbose --clean --no-owner --no-acl --format=c #{db} > #{Rails.root}/db/#{app}.dump"
	end
	puts cmd

	# -- encoding : utf-8 --
	module PayStripeHelpers
	# must be used with driver: :selenium (or :sauce?)
	def pay_stripe
	sleep(0.7) # wait for the js to create the popup in response to pressing the button
	within_frame 'stripe_checkout_app' do # must be selenium
	# fill_in 'card_number', with: '4242424242424242' no longer works
	4.times {page.driver.browser.find_element(:id, 'card_number').send_keys('4242')}

	# fill_in 'cc-exp', with: '5/2018' no longer works

	=begin

	Include in your rspec config like so:

	RSpec.configure do \|spec\|
	spec.include RSpec::RedisHelper, redis: true
	end

	This helper will clean redis around each example.
	=end

	Agnes en_US # Isn't it nice to have a computer that will talk to you?
	Albert en_US # I have a frog in my throat. No, I mean a real frog!
	Alex en_US # Most people recognize me by my voice.
	Alice it_IT # Salve, mi chiamo Alice e sono una voce italiana.
	Alva sv_SE # Hej, jag heter Alva. Jag är en svensk röst.
	Amelie fr_CA # Bonjour, je m’appelle Amelie. Je suis une voix canadienne.
	Anna de_DE # Hallo, ich heiße Anna und ich bin eine deutsche Stimme.
	Bad News en_US # The light you see at the end of the tunnel is the headlamp of a fast approaching train.
	Bahh en_US # Do not pull the wool over my eyes.
	Bells en_US # Time flies when you are having fun.