中野三玖 dagrons

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

PSQL

Magic words:

psql -U postgres

Some interesting flags (to see all, use -h or --help depending on your psql version):

-E: will describe the underlaying queries of the \ commands (cool for learning!)
-l: psql will list all databases and then exit (useful if the user you connect with doesn't has a default database, like at AWS RDS)

Tabs and Windows

Function	Shortcut
New Tab	`⌘` + `T`
Close Tab or Window	`⌘` + `W` (same as many mac apps)
Go to Tab	`⌘` + `Number Key` (ie: `⌘2` is 2nd tab)
Go to Split Pane by Direction	`⌘` + `Option` + `Arrow Key`
Cycle iTerm Windows	`⌘` + `backtick` (true of all mac apps and works with desktops/mission control)

	<keymap version="1" name="Emacs copy" parent="Emacs">
	<action id="AceAction">
	<keyboard-shortcut first-keystroke="alt enter" />
	</action>
	<action id="ActivateTerminalToolWindow">
	<keyboard-shortcut first-keystroke="alt f12" />
	<keyboard-shortcut first-keystroke="alt j" />
	</action>
	<action id="Adtui.ZoomInAction">
	<keyboard-shortcut first-keystroke="ctrl add" />

	/*
	* This document is provided to the public domain under the
	* terms of the Creative Commons CC0 public domain license
	*/

	How to boot Arch Linux ARM in QEMU (patched for M1)

	Prerequisites:

	QEMU - patched for M1 processors - patches: https://github.com/utmapp/qemu

	channels:
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/main/
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/pkgs/free/
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/conda-forge/
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/Paddle/
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/fastai/
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/pytorch/
	- http://mirrors.tuna.tsinghua.edu.cn/anaconda/cloud/bioconda/
	show_channel_urls: true
	ssl_verify: false

	#!/bin/bash

	set -e

	# run as root
	if [[ "$(whoami)" != "root" ]]; then
	exit -1
	fi

	addgroup clash

	# Generated by iptables-save v1.8.7 on Sat May 28 03:15:57 2022
	*raw
	:PREROUTING ACCEPT [10334:1353326]
	:OUTPUT ACCEPT [9660:1339648]
	COMMIT
	# Completed on Sat May 28 03:15:57 2022
	# Generated by iptables-save v1.8.7 on Sat May 28 03:15:57 2022
	*nat
	:PREROUTING ACCEPT [3:180]
	:INPUT ACCEPT [0:0]

	# Check disk space before
	df -h

	# Delete local-lvm storage in gui

	lvremove /dev/pve/data

	lvresize -l +100%FREE /dev/pve/root

	resize2fs /dev/mapper/pve-root

	#!/bin/bash

	# tested on ubuntu18.04-desktop

	set -e
	set -x

	# confs
	VBOX_USER=$(cat /etc/passwd\|grep 1000\|cut -d ':' -f 1)
	VBOX_PASS="1205"