lakshmankashyap

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++;}

lakshmankashyap

// 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

lakshmankashyap

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?

lakshmankashyap

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:

• ECMAScript 6 Language specification
• ECMAScript 5 Language specification
• MDN
• The Modern JavaScript Tutorial

General Notes

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

lakshmankashyap

# 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

lakshmankashyap

MongoDB - Setting up a Replica Set

cd \mongodbdir\

mkdir db1
mkdir db2
mkdir db3

Primary

lakshmankashyap

fork_mode.js

var child_process = require('child_process');
var cpus = require('os').cpus();
var net = require('net');
var tcpSrv = net.createServer();

tcpSrv.listen(8000, function() {
    for (var i = 1; i <= cpus.length; i++) {

lakshmankashyap

// sending to sender-client only
socket.emit('message', "this is a test");

// sending to all clients, include sender
io.emit('message', "this is a test");

// sending to all clients except sender
socket.broadcast.emit('message', "this is a test");

// sending to all clients in 'game' room(channel) except sender

lakshmankashyap

REM
REM Setup a MongoDB Sharded Cluster
REM
REM Reference: http://cookbook.mongodb.org/operations/convert-replica-set-to-replicated-shard-cluster/
REM More Info: http://www.kchodorow.com/blog/2010/08/09/sharding-and-replica-sets-illustrated/
REM

REM Download and Unpack MongoDB Software
REM
SET URL="https://fastdl.mongodb.org/win32/mongodb-win32-x86_64-2008plus-2.6.11.zip"