ameenkhan07

What to Expect and Tips

• 45-minute systems interview, focus on responding to real world problems with an unhealthy service, such as a web server or database. The interview will start off at a high level troubleshooting a likely scenario, dig deeper to find the cause and some possible solutions for it. The goal is to probe your knowledge of systems at scale and under load, so keep in mind the challenges of the Facebook environment.
• Focus on things such as tooling, memory management and unix process lifecycle.

Systems

More specifically, linux troubleshooting and debugging. Understanding things like memory, io, cpu, shell, memory etc. would be pretty helpful. Knowing how to actually write a unix shell would also be a good idea. What tools might you use to debug something? On another note, this interview will likely push your boundaries of what you know (and how to implement it).

Design/Architecture 

Interview is all about taking an ambiguous question of how you might build a system and letting

anushadasari

def a_method(a,b)
  a + yield(a,b)
end

a_method(1,2) {|x,y| (x + y) * 3}


def another_method
  return yield if block_given?
  'no_block'

giannisp

After automatically updating Postgres to 10.0 via Homebrew, the pg_ctl start command didn't work.
The error was "The data directory was initialized by PostgreSQL version 9.6, which is not compatible with this version 10.0."

Database files have to be updated before starting the server, here are the steps that had to be followed:

# need to have both 9.6.x and latest 10.0 installed, and keep 10.0 as default
brew unlink postgresql
brew install postgresql@9.6
brew unlink postgresql@9.6
brew link postgresql

vasanthk

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

1. Clarify and agree on the scope of the system

• User cases (description of sequences of events that, taken together, lead to a system doing something useful)
  • Who is going to use it?
  • How are they going to use it?

jniltinho

package main

/*
URL: https://github.com/mccoyst/myip/blob/master/myip.go
URL: http://changsijay.com/2013/07/28/golang-get-ip-address/
*/

import (
	"net"
	"os"

pithyless

class Integer
  N_BYTES = [42].pack('i').size
  N_BITS = N_BYTES * 16
  MAX = 2 ** (N_BITS - 2) - 1
  MIN = -MAX - 1
end

p Integer::MAX              #=> 4611686018427387903
p Integer::MAX.class        #=> Fixnum
p (Integer::MAX + 1).class  #=> Bignum

jkraemer

require 'rufus/scheduler'
class Scheduler

  # Starts the scheduler unless it is already running
  def self.start_unless_running(pid_file)
    with_lockfile(File.join(File.dirname(pid_file), 'scheduler.lock')) do
      if File.exists?(pid_file)
        pid = IO.read(pid_file).to_i
        if pid > 0 && process_running?(pid)
          puts "not starting scheduler because it already is running with pid #{pid}"

trey

Creating a Happy Git Environment on OS X

Step 1: Install Git

brew install git bash-completion

Configure things:

git config --global user.name "Your Name"

git config --global user.email "you@example.com"

rtekie

# Please refer to http://ctoinsights.wordpress.com/2011/10/17/running-distributed-cron-jobs-in-the-cloud/
class DatabaseSemaphore < ActiveRecord::Base
  validates_presence_of :name, :message => "can't be blank"

  def self.open?(name, lock_duration = 600)
  # only one requestor can get open semaphore at a time
  # sempahore can be locked in a closed position for lock_duration in seconds
    semaphore_open = false
    now = Time.now
    # insert record if it does not exist yet

danmackinlay

#! /bin/sh
### BEGIN INIT INFO
# Provides:          supervisord
# Required-Start:    $remote_fs
# Required-Stop:     $remote_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Example initscript
# Description:       This file should be used to construct scripts to be
#                    placed in /etc/init.d.