Jiho Lee DPS0340

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

tmux cheat sheet

(C-x means ctrl+x, M-x means alt+x)

Prefix key

The default prefix is C-b. If you (or your muscle memory) prefer C-a, you need to add this to ~/.tmux.conf:

remap prefix to Control + a

tmux shortcuts & cheatsheet

start new:

tmux

start new with session name:

tmux new -s myname

In August 2007 a hacker found a way to expose the PHP source code on facebook.com. He retrieved two files and then emailed them to me, and I wrote about the issue:

http://techcrunch.com/2007/08/11/facebook-source-code-leaked/

It became a big deal:

http://www.techmeme.com/070812/p1#a070812p1

The two files are index.php (the homepage) and search.php (the search page)

	I turned this gist into a "real" repository. It is here: http://github.com/pete/cats .


	Here, placed side-by-side for comparison, are GNU's implementation of
	cat, Plan 9's implementation, Busybox's implementation, and NetBSD's
	implementation, Seventh Edition Unix (1979), and 4.3BSD.

	For good measure (and because I suppose I am now committed to collecting
	cats) also included are Second Edition Unix (in assembly) and Inferno's
	implementation (in Limbo) for good measure.

	(define (zip-cons a b)
	(if (null? a)
	'()
	(cons (cons (car a) (car b))
	(zip-cons (cdr a) (cdr b)))))

	(define (p c r)
	(cond
	((null? c) (map (lambda (x) '()) r))
	((eq? (car c) (caar r))

	/*POSIX/Linux multithreaded socket test
	Copyright (c) 2006-2007 Richard Palethorpe

	Permission is hereby granted, free of charge, to any person obtaining a copy of this
	software and associated documentation files (the "Software"), to deal in the Software
	without restriction, including without limitation the rights to use, copy, modify,
	merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
	permit persons to whom the Software is furnished to do so, subject to the following
	conditions:

	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

	-- show running queries (pre 9.2)
	SELECT procpid, age(clock_timestamp(), query_start), usename, current_query
	FROM pg_stat_activity
	WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%'
	ORDER BY query_start desc;

	-- show running queries (9.2)
	SELECT pid, age(clock_timestamp(), query_start), usename, query
	FROM pg_stat_activity
	WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%'