Rahul Jyala RahulJyala7

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?

This will guide you through setting up a replica set in a docker environment using.

Docker Compose
MongoDB Replica Sets
Mongoose
Mongoose Transactions

Thanks to https://gist.github.com/asoorm for helping with their docker-compose file!

Depth in Event Loop

For those JavaScript programmers, event loop is an important concept, inevitably.

Literally, event loop is what JavaScritp uses to implement non-blocking execution. Understanding how the event loops works internally would benefit you a lot when programming in JavaScript.

There are two major environments JavaScript runs in: browser and Node.js.

Browser

Shallow

Real unit test (isolation, no children render)

Simple shallow

Calls:

constructor
render

Inspired by this article. Neat tricks for speeding up integer computations.

Note: cin.sync_with_stdio(false); disables synchronous IO and gives you a performance boost. If used, you should only use cin for reading input (don't use both cin and scanf when sync is disabled, for example) or you will get unexpected results.

Multiply by a power of 2

x = x << 1; // x = x * 2

	Latency Comparison Numbers (~2012)
	----------------------------------
	L1 cache reference 0.5 ns
	Branch mispredict 5 ns
	L2 cache reference 7 ns 14x L1 cache
	Mutex lock/unlock 25 ns
	Main memory reference 100 ns 20x L2 cache, 200x L1 cache
	Compress 1K bytes with Zippy 3,000 ns 3 us
	Send 1K bytes over 1 Gbps network 10,000 ns 10 us
	Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD

	Mutex: exclusive-member access to a resource

	Semaphore: n-member access to a resource

	That is, a mutex can be used to syncronize access to a counter, file, database, etc.

	A sempahore can do the same thing but supports a fixed number of simultaneous callers. For example, I can wrap my database calls in a semaphore(3) so that my multithreaded app will hit the database with at most 3 simultaneous connections. All attempts will block until one of the three slots opens up. They make things like doing naive throttling really, really easy.


	function Semaphore(max) {

	// MONGO COMMAND LINE
	// start mongod
	ulimit -n 2048 && mongod
	// ctrl-c ends in same window, but can also use
	killall mongod
	// start mongod with data directory in another location
	mongod -dbpath /path/to/data/dir
	// open command line interface (mongo shell)
	mongo
	// restore a DB dump from a binary (BSON) dump file

	version: "3"
	services:
	mongo1:
	hostname: mongo1
	container_name: localmongo1
	image: mongo:4.0-xenial
	expose:
	- 27017
	ports:
	- 27011:27017