cstorey

A little Clojure configuration reader

This is a handy bit of code I've written more than once. I thought I'd throw it in here so I can refer back to it later. Basically, it lets you read a config file to produce a Clojure map. The config files themselves can contain one or more forms, each of which can be either a map or a list. Maps are simply merged. Lists correspond to invocations of extension points, which in turn produces a map, which is merged along with everything else.

An Example

Consider the following files:

names.edn

We have some systems at work that use the database as a queue. I've been thinking about this a bit. So have other people.

RapGenius has an interesting post about Heroku's randomized load balancing, complaining about how random placement degrades performance compared to prior omniscient approaches. RapGenius ran some simulations, including an experiments with a "Choice of Two" method:

Choice of two routing is the naive method from before, with the twist that when you assign a request to a random dyno, if that dyno is already busy then you reassign the request to a second random dyno, with no regard for whether the second dyno is busy

This differs subtly but substantially from the standard "Power of Two Choices" randomized load balancing:

each [request] is placed in the least loaded of d >= 2 [Dynos] chosen independently and uniformly at random

Take a look at the difference in queue lengths below, for 200 Dynos, 100

	Hello scala, my old friend
	I've come to take you home again
	Because a feature slowly creeping
	left me plagued with doubts and weeping
	and the version that was tagged in the repo
	just has to go
	it lacks the signs of soundness

	On sleepless nights I hacked alone
	applying ant and other tools of stone

	#!/usr/bin/ruby

	require 'twitter'
	require 'marky_markov'

	def tweets
	block = Twitter.user_timeline("joedamato", count: 200)
	text = block.map(&:text)
	max = block.last.id
	until block.empty?

	// Boilerplate
	function objectUnion(definer) {
	var defined = 0, length = 0, isDefined = false, definitions, key;

	definitions = definer(function() {
	var names = arguments, fold;
	if(isDefined) {
	throw new TypeError('This objectUnion has already been defined');
	}
	function Ctor() {}

	(ns net.cgrand.decay
	"Exponentially decaying lists. See http://awelonblue.wordpress.com/2013/01/24/exponential-decay-of-history-improved/
	for background and http://clj-me.cgrand.net/2013/02/12/decaying-lists-log-scale-for-lists/ for documentation")

	;; PRNG, formulas straight from java.util.Random javadoc
	(defn- seed ^long [^long n]
	(bit-and (unchecked-multiply n 0x5DEECE66D)
	(unchecked-dec (bit-shift-left 1 48))))

	(defn- next-seed ^long [^long seed]

	# A demonstration of the CurveCP handshake protocol. This protocol has many
	# favorable security properties described at http://curvecp.org.
	#
	# In addition to its security advantages, it has the following favorable properties:
	# * Needs only 2 messages (1 from client, 1 from server) before application
	# messages can be exchanged (3 before the server can send application messages)
	# * Does not require the server to keep protocol state between handshake messages.
	#
	# An overview of the protocol:
	#

	#!/usr/bin/env ruby

	require 'rubygems'
	require 'bundler/setup'
	require 'celluloid'

	class Table
	include Celluloid
	CHOPSTICK_FREE = 0
	CHOPSTICK_USED = 1

	package ;

	// hots classes
	using hots.ImplicitInstances;
	using hots.ImplicitCasts;

	// Javascript API
	import js.JQuery;
	import js.Lib;
	import js.Browser.document;