Anagh Kumar Baranwal darthShadow

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

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?

Exporting your 2FA tokens from Authy to transfer them into another 2FA application

IMPORTANT - Update regarding deprecation of Authy desktop apps

Past August 2024, Authy stopped supported the desktop version of their apps:
See Authy is shutting down its desktop app | The 2FA app Authy will only be available on Android and iOS starting in August for details.

And indeed, after a while, Authy changed something in their backend which now prevents the old desktop app from logging in. If you are already logged in, then you are in luck, and you can follow the instructions below to export your tokens.

If you are not logged in anymore, but can find a backup of the necessary files, then restore those files, and re-install Authy 2.2.3 following the instructions below, and it should work as expected.

Installing Fish shell on MacOS (Intel and M1) using brew

Fish is a smart and user-friendly command line (like bash or zsh). This is how you can instal Fish on MacOS and make your default shell.

Note that you need the https://brew.sh/ package manager installed on your machine.

Install Fish

brew install fish

This was a huge hassle to figure out, so I wrote up a little guide in hopes that others would find it helpful:

How to convince macOS to do IPv6 DNS lookups when your only IPv6 address is via a VPN or tunnel of some sort

The Problem

macOS's domain name resolver will only return IPv6 addresses (from AAAA records) when it thinks that you have a valid routable IPv6 address. For physical interfaces like Ethernet or Wi-Fi it's enough to set or be assigned an IPv6 address, but for tunnels (such as those using utun interfaces) there are some extra annoying steps that need to be taken to convince the system that yes, you indeed have an IPv6 address, and yes, you'd like to get IPv6 addresses back for DNS lookups.

I use wg-quick to establish a WireGuard tunnel between my laptop and a Linode virtual server. WireGuard uses a utun user-space tunnel device to make the connection. Here's how that device gets configured:

Question

Forum topic: https://airvpn.org/topic/25140-the-issue-your-browser-is-avoiding-ipv6/ Ipv6 test: http://test-ipv6.com/

In the forum thread AirVPN writes:

Our assigned ULAs are in fde6:7a:7d20::/48 which is inside the range officially reserved to ULA so we don't understand why a browser should discriminate against them in favor of a local IPv4 address...

I hope to answer this question in this document.

	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

	#!/usr/bin/env python3

	'''
	calisuck: index, filter-out smartly and download ebooks from Calibre open directories

	Installation:

	You need python 3.5 installed

	Download the file as a zip and unzip-it and get into the dir

	<!-- Put in ./Library/Application Support/Plex Media Server/Profiles/Android-SHIELD Android TV.xml -->
	<!-- Author: Donald Webster fryfrog@gmail.com -->
	<?xml version="1.0" encoding="utf-8"?>
	<Client name="SHIELD Android TV">
	<Identification>
	<Header name="User-Agent" substring="SHIELD Android TV" />
	</Identification>
	<TranscodeTargets>
	<VideoProfile container="mkv" codec="h264" audioCodec="aac" context="streaming" />
	<MusicProfile container="flac" codec="flac" id="StereoMusicTranscodeProfile" />

	UID=1000
	TLD=mydomain.com

	# ACME
	ACME_EMAIL=admin@mydomain.com
	CLOUDFLARE_EMAIL=admin@mydomain.com
	CLOUDFLARE_API_KEY=xxxx

	# OAUTH
	OAUTH_CLIENT_ID=xxxx