Lakshman lakshmankashyap

Instead of writing a long article I wrote this summary to give a good overview about software systems scalability by listing the main terms and methodologies that widely used to build stable systems that are able to scale and handle the increasing amont of users and data.

Index

Scalability
Terms System Quality Attributes
Failover
Load Balancer
MapReduce
Caching

Javascript Deep Dive

This document is written to help JavaScript developers to understand JavaScript's weird parts deeply and to prepare for interviews, the following resources was really helpful to write this document:

General Notes

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?

Node.js interview questions

What is the architecture of node?

Application & Modules

This is where you write your application & installed modules live. Usually they are written in plain Javascript.

C/C++ bindings

Install Robo3t On Ubuntu 18.04

Download the package form Robo3t or using `wget`

wget https://download.robomongo.org/1.2.1/linux/robo3t-1.2.1-linux-x86_64-3e50a65.tar.gz

Extract here using

tar -xvzf robo3t-1.2.1-linux-x86_64-3e50a65.tar.gz

	# Setup local MongoDB Replica Set for development.

	DB_ROOT ?= /tmp
	DB1_PATH ?= ${DB_ROOT}/db1
	DB2_PATH ?= ${DB_ROOT}/db2
	DB3_PATH ?= ${DB_ROOT}/db3
	DB1_PORT ?= 30000
	DB2_PORT ?= 40000
	DB3_PORT ?= 50000

	// the main app file
	import express from "express";
	import loadDb from "./loadDb"; // dummy middleware to load db (sets request.db)
	import authenticate from "./authentication"; // middleware for doing authentication
	import permit from "./permission"; // middleware for checking if user's role is permitted to make request

	const app = express(),
	api = express.Router();

	// first middleware will setup db connection

	db.link_access.group(
	{
	keyf: function(doc) {
	var date = new Date(doc.date);
	var dateKey = (date.getMonth()+1)+"/"+date.getDate()+"/"+date.getFullYear()+'';
	return {'day': dateKey};
	},
	cond: {short_id: "N"},
	initial: {count:0},
	reduce: function(obj, prev) {prev.count++;}

	var mention_id = 620996;

	db.mentionStats.aggregate([
	{ $match: {'mention_id': mention_id}},
	{ $group: {'_id': {
	'year': { '$year': "$verification_date" },
	'month': { '$month': "$verification_date" },
	'day': { '$dayOfMonth': "$verification_date" }
	},
	'retweets': { $last: "$retweets" }}},

	var start = new Date(2013, 5, 4)
	var end = new Date(2013, 5, 6)
	db.mention_stat.find({"verification": {"$gte": start, "$lt": end}})