Jonas Collberg joncol

This document is a short how-to. It doesn't contain a lot of details about each change you need to implement, but it contains lots of links to the corresponding documents. Please read these docs for refetence.

Upgrade process in general.

1. Setup eslint

ESLint is the main tool to find deprecations in the code so first of all we need to configure it properly.

Prerequisites

Using PostgreSQL Advisory Locks in Haskell

Recently two different administrative users of a Haskell app I maintain started a long-running background job at the same time. This resulted in some Bad Things happening which I would like to prevent in the future!

So I want a lock. This app runs on at least two servers at any given time, so it needs to be a distributed lock, and for Reasons (not relevant to this blogpost) I can't use our Redis cache. So the PostgreSQL database it is!

My Vim-related gists

Long-form

Commit Message Guidelines

Short (72 chars or less) summary

More detailed explanatory text. Wrap it to 72 characters. The blank
line separating the summary from the body is critical (unless you omit
the body entirely).

Write your commit message in the imperative: "Fix bug" and not "Fixed
bug" or "Fixes bug." This convention matches up with commit messages

Installation of NixOS with encrypted root

These are my notes on instaling NixOS 16.03 on a Lenovo ThinkPad X1 Carbon (4th generation) with an encrypted root file system using UEFI.

Most of this is scrambled from the following pages:

	#!/usr/bin/env bash
	set -Eeuxo pipefail

	# Set up git
	git init
	gitignore haskell
	echo '*.cabal' >> .gitignore

	# Set up niv
	niv init


	-- important: compile with -threaded

	import Control.Concurrent.STM
	import Control.Applicative

	-- \|Wait for STM action specified amount of time and return value of action or default value if action times out
	stmTimeout' :: Int -> a -> STM a -> IO a
	stmTimeout' microseconds defVal f
	= registerDelay microseconds

	(defn classes-of
	"Get the classes of an element as a Clojure keyword vector."
	[e]
	(let [words (-> e (.getAttribute "class") (string/split " "))]
	(mapv keyword words)))

	(defn classes->str
	"Change a Clojure keyword seq into an HTML class string."
	[classes]
	(->> classes (mapv name) (string/join " ")))

	; Postgres listen/notify in Clojure using http://impossibl.github.io/pgjdbc-ng/

	; in project.clj dependencies
	; [com.impossibl.pgjdbc-ng/pgjdbc-ng "0.5"]


	(ns pglisten.core
	(:import [com.impossibl.postgres.jdbc PGDataSource]
	[com.impossibl.postgres.api.jdbc PGNotificationListener]))

	use --property print.key=true

	Example : ./kafka-console-consumer.sh --bootstrap-server <BROKERS_ADDRESS> --topic <YOUR_TOPIC> --property print.key=true