Jian Yuan Lee jianyuan

System Design Cheatsheet

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

Basic Steps

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?

These are the Kickstarter Engineering and Data role definitions for both teams.

Technical	Data	People
Junior Software Engineer
Software Engineer	Data Analyst
Senior Software Engineer	Data Scientist	Engineering Manager
Staff Engineer	VP of Data	Engineering Director
Principal Engineer		CTO

Interface Versioning (InterVer)

Never break backcompat, keep the API nimble

An extension of SemVer with a stricter (yet more realistic) backcompat guarantee, that provides more flexibility to change the API, for libraries that are packaged and downloaded (not services accessed remotely over the Internet (see Note 4)).

This guide assumes that you recently run brew upgrade postgresql and discovered to your dismay that you accidentally bumped from one major version to another: say 9.3.x to 9.4.x. Yes, that is a major version bump in PG land.

First let's check something.

brew info postgresql

The top of what gets printed as a result is the most important:

Update, September 2016

OK, you can pretty much ignore what I wrote below this update, because it doesn't really apply anymore.

I wrote this over a year ago, and at the time I had spent a couple of weeks trying to get Kafka 0.8 working with .NET and then Node.js with much frustration and very little success. I was rather angry. It keeps getting linked, though, and just popped up on Hacker News, so here's sort of an update, although I haven't used Kafka at all this year so I don't really have any new information.

In the end, we managed to get things working with a Node.js client, although we continued to have problems, both with our code and with managing a Kafka/Zookeeper cluster generally. What made it worse was that I did not then, and do not now, believe that Kafka was the correct solution for that particular problem at that particular company. What they were trying to achieve could have been done more simply with any number of other messaging systems, with a subscriber reading messages off and writing

	type Spell =
	{ Name : string
	Cost : int
	Damage : int
	Heal : int
	Armor : int
	Mana : int
	Duration : int }

	let allSpells =

	#!/usr/bin/sudo sh

	## ruby_revealer.sh -- decrypt obfuscated GHE .rb files. 2.0.0 to 2.3.1+.

	## From `strings ruby_concealer.so`:
	##
	## > This obfuscation is intended to discourage GitHub Enterprise customers
	## > from making modifications to the VM.
	##
	## Well, good, as long as its not intended to discourage me from doing this!

	# tested with celery[redis]==3.1.17

	# to run with default configuration -- tasks will take 14 seconds to complete the 20 tasks in start_all() below

	celery worker -A cluster_project.celery_app -Q tester -lINFO --concurrency=4

	# to run with -Ofair -- tasks will take 10 seconds to complete

	celery worker -A cluster_project.celery_app -Q tester -lINFO --concurrency=4 -Ofair

	#!/usr/bin/env bash

	ENV_PATH="$(dirname "$(dirname "$(which pip)")")"
	SYSTEM_VIRTUALENV="$(which -a virtualenv\|tail -1)"

	BAD_ENV_PATHS="/usr/local"

	echo "Ensure the root of the broken virtualenv:"
	echo " $ENV_PATH"

	users = User.arel_table
	query = users.project(users[Arel.star])