Cheewai cynici

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

Put a closure on it

Sometimes you'll have objects that manage state along with event handling. This happens frequently in MVC apps. Let's start with a messy example:

var Launcher = function(rocket) {
  this.rocket = rocket
}

Launcher.prototype.isReady = function() {

ANNOUNCEMENT

I have moved this over to the Tech Interview Cheat Sheet Repo and has been expanded and even has code challenges you can run and practice against!

\

Rich Hickey on becoming a better developer

Rich Hickey • 3 years ago

Sorry, I have to disagree with the entire premise here.

A wide variety of experiences might lead to well-roundedness, but not to greatness, nor even goodness. By constantly switching from one thing to another you are always reaching above your comfort zone, yes, but doing so by resetting your skill and knowledge level to zero.

Mastery comes from a combination of at least several of the following:

What is the appeal of dynamically-typed languages?

Kris Nuttycombe asks:

I genuinely wish I understood the appeal of unityped languages better. Can someone who really knows both well-typed and unityped explain?

I think the terms well-typed and unityped are a bit of question-begging here (you might as well say good-typed versus bad-typed), so instead I will say statically-typed and dynamically-typed.

I'm going to approach this article using Scala to stand-in for static typing and Python for dynamic typing. I feel like I am credibly proficient both languages: I don't currently write a lot of Python, but I still have affection for the language, and have probably written hundreds of thousands of lines of Python code over the years.

GPG / Mutt / Gmail

About

This is a collection of snippets, not a comprehensive guide. I suggest you start with Operational PGP.

Here is an incomplete list of things that are different from other approaches:

I don't use keyservers. Ever.
Yes, I use Gmail instead of some bespoke hipster freedom service

	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

	Use tcpdump to monitor mysql

	# Capture the packets
	sudo tcpdump -i eth0 port 3306 -s 65535 -x -n -q -tttt > tcpdump.out

	# analyze all the requests from a given host
	pt-query-digest --type=tcpdump --filter '($event->{host} \|\| $event->{ip} \|\| "") =~ m/192.168.248.64/' tcpdump.out

	# This is an example of the Stack Exchange Tier 1 HAProxy config
	# The only things that have been changed from what we are running are:
	# 1. User names have been removed
	# 2. All Passwords have been remove
	# 3. IPs have been changed to use the example/documentation ranges
	# 4. Rate limit numbers have been changed to randome numbers, don't read into them

	userlist stats-auth
	group admin users $admin_user
	user $admin_user insecure-password $some_password

	HAPROXYTIME (?!<[0-9])%{HOUR}:%{MINUTE}(?::%{SECOND})(?![0-9])
	HAPROXYDATE %{MONTHDAY}/%{MONTH}/%{YEAR}:%{HAPROXYTIME}.%{INT}

	HAPROXYHTTP <%{BASE10NUM}>%{SYSLOGTIMESTAMP} %{SYSLOGPROG}: %{IP:client}:%{INT:port} \[%{HAPROXYDATE:accept_date}\] %{NOTSPACE:frontend_name} %{NOTSPACE:backend_name}/%{NOTSPACE:server_name} %{INT:time_request}/%{INT:time_queue}/%{INT:time_backend_connect}/%{INT:time_backend_response}/%{NOTSPACE:time_duration} %{INT:http_status_code} %{NOTSPACE:bytes_read} %{DATA:captured_request_cookie} %{DATA:captured_response_cookie} %{NOTSPACE:termination_state} %{INT:actconn}/%{INT:feconn}/%{INT:beconn}/%{INT:srvconn}/%{NOTSPACE:retries} %{INT:srv_queue}/%{INT:backend_queue} \"(<BADREQ>\|(%{WORD:http_verb} (%{URIPROTO:http_proto}://)?(?:%{USER:http_user}(?::[^@]*)?@)?(?:%{URIHOST:http_host})?(?:%{URIPATHPARAM:http_request})?( HTTP/%{NUMBER:http_version})?))?\"