Sam Qiu samqiu

Sample service script for debianoids

Look at LSB init scripts for more information.

Usage

Copy to /etc/init.d:

# replace "$YOUR_SERVICE_NAME" with your service's name (whenever it's not enough obvious)

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

Scaling your API with rate limiters

The following are examples of the four types rate limiters discussed in the accompanying blog post. In the examples below I've used pseudocode-like Ruby, so if you're unfamiliar with Ruby you should be able to easily translate this approach to other languages. Complete examples in Ruby are also provided later in this gist.

In most cases you'll want all these examples to be classes, but I've used simple functions here to keep the code samples brief.

Request rate limiter

This uses a basic token bucket algorithm and relies on the fact that Redis scripts execute atomically. No other operations can run between fetching the count and writing the new count.

	# 在本地服务器建立 rubygems.org 的镜像缓存，以提高 gem 的安装速度
	# 此配置设置缓存过期为1天，也就是说，新上的 gem 无法马上安装
	# 做这个起什么作用？
	# rubygems 的很多资源文件是存放到 Amazon S3 上面的，由于 GFW 对某些 S3 服务器又连接重置或丢包，导致 gem 安装异常缓慢或有时候根本无法连接安装。
	# 而通过这种跳板的方式可以很好的解决这个问题，当然前提是 Nginx反向代理服务器需要在国外

	proxy_cache_path /var/cache/rubygems levels=1:2 keys_zone=RUBYGEMS:10m
	inactive=24h max_size=1g;
	server {
	listen 80;

	gifify() {
	if [[ -n "$1" ]]; then
	if [[ $2 == '--good' ]]; then
	ffmpeg -i $1 -r 10 -vcodec png out-static-%05d.png
	time convert -verbose +dither -layers Optimize -resize 600x600\> out-static*.png GIF:- \| gifsicle --colors 128 --delay=5 --loop --optimize=3 --multifile - > $1.gif
	rm out-static*.png
	else
	ffmpeg -i $1 -s 600x400 -pix_fmt rgb24 -r 10 -f gif - \| gifsicle --optimize=3 --delay=3 > $1.gif
	fi
	else

	# This is just a cheat sheet:

	# On production
	sudo -u postgres pg_dump database \| gzip -9 > database.sql.gz

	# On local
	scp -C production:~/database.sql.gz
	dropdb database && createdb database
	gunzip < database.sql.gz \| psql database

	/**
	* Check if a given ip is in a network
	* @param string $ip IP to check in IPV4 format eg. 127.0.0.1
	* @param string $range IP/CIDR netmask eg. 127.0.0.0/24, also 127.0.0.1 is accepted and /32 assumed
	* @return boolean true if the ip is in this range / false if not.
	*/
	function ip_in_range( $ip, $range ) {
	if ( strpos( $range, '/' ) == false ) {
	$range .= '/32';
	}

	%!TEX program = xelatex
	% Font Size:
	% 10pt, 11pt, 12pt
	% Paper Size:
	% a4paper, letterpaper, a5paper, leagalpaper, executivepaper, landscape
	% Font Family:
	% roman, sans
	\documentclass[12pt, a4paper, roman]{moderncv}

	% Style:

	# see https://www.topbug.net/blog/2013/04/14/install-and-use-gnu-command-line-tools-in-mac-os-x/

	# core
	brew install coreutils

	# key commands
	brew install binutils
	brew install diffutils
	brew install ed --default-names
	brew install findutils --with-default-names