Alex NOX73

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

Zero downtime deploys with unicorn + nginx + runit + rvm + chef

Below are the actual files we use in one of our latest production applications at Agora Games to achieve zero downtime deploys with unicorn. You've probably already read the GitHub blog post on Unicorn and would like to try zero downtime deploys for your application. I hope these files and notes help. I am happy to update these files or these notes if there are comments/questions. YMMV (of course).

Other application notes:

Our application uses MongoDB, so we don't have database migrations to worry about as with MySQL or postgresql. That does not mean that we won't have to worry about issues with the database with indexes being built in MongoDB or what have you.
We use capistrano for deployment.

Salient points for each file:

Howto Reset etcd discovery

Every time my test cluster is going down, I was struggeling with etcd autodiscovery failing. This looks probably familiar to you:

The Problem

systemd[1]: Starting etcd...
systemd[1]: Started etcd.
etcd[3066]: [etcd] Apr  9 08:31:42.512 INFO      | Discovery via https://discovery.etcd.io using prefix /<TOKEN>.

	# usage:
	# it "should return a result of 5" do
	# eventually { long_running_thing.result.should eq(5) }
	# end
	module AsyncHelper
	def eventually(:options = {})
	timeout = options[:timeout] \|\| 2
	interval = options[:interval] \|\| 0.1
	time_limit = Time.now + timeout
	loop do

	after "deploy:symlink", "deploy:restart_workers"
	after "deploy:restart_workers", "deploy:restart_scheduler"

	##
	# Rake helper task.
	# http://pastie.org/255489
	# http://geminstallthat.wordpress.com/2008/01/27/rake-tasks-through-capistrano/
	# http://ananelson.com/said/on/2007/12/30/remote-rake-tasks-with-capistrano/
	def run_remote_rake(rake_cmd)
	rake_args = ENV['RAKE_ARGS'].to_s.split(',')

	-- show running queries (pre 9.2)
	SELECT procpid, age(clock_timestamp(), query_start), usename, current_query
	FROM pg_stat_activity
	WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%'
	ORDER BY query_start desc;

	-- show running queries (9.2)
	SELECT pid, age(clock_timestamp(), query_start), usename, query
	FROM pg_stat_activity
	WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%'

	set :branch do
	tag = ENV['TAG'] \|\| Capistrano::CLI.ui.ask("What tag do you want to deploy? ")

	if tag.empty?
	logger.important 'tag is emtpy, exiting'
	exit
	else
	tag
	end
	end

	#### Tmux configuration file ####
	# \; - used for separating commands on binding

	# Right colors for tmux
	set -g default-terminal 'screen-256color'

	# remapping command prefix to "Ctrl + a" and unbind "Ctrl+b"
	set -g prefix C-a
	unbind C-b

	#!/bin/bash

	function tmux_web {
	SESSION_NAME=$1
	#echo "Create.."
	tmux new -s $SESSION_NAME -n editor -d
	#echo "Creat first pane (editor).."
	tmux send-keys -t $SESSION_NAME 'vim' C-m
	#echo "Run vim in first pane.."
	tmux new-window -n console -t $SESSION_NAME