Everythings on dlow's blog

SLO and burn rate

Thu, 22 Apr 2021 09:19:25 +0100

In this post, I want to share my understanding of burn monitor and the calculations behind it. I’ll cover the definitions, the link between SLO target, burn rate target and error rate target. We’ll go on a journey to understand how we will arrive at the number 14.4. Hopefully this gives a different perspective or serves as a guide when reading the [chapter in the SRE book: alerting on SLO]¹.

bubble sort and tetrahedral numbers

Wed, 14 Apr 2021 10:17:36 +0100

Today I had a very simple problem in one of my Golang side projects. I have a server that retrieves a JSON array of objects that have the same schema and I want to display them in a server side rendered HTML table on a web page¹. If I had unlimited time, I would probably have started a Create-React-App project and stick in a popular table library that takes care of rendering this JSON object. However, that workflow requires building the Single Page App and then I probably have to embed it in the server. That’s a bit too much effort for me as I wanted something more php-esque.

Liar's paradox and truthfulness of statements

Sun, 13 Sep 2020 10:18:25 +0100

An essay on truthfulness of statements and what we can learn from them

Reflections on note taking software

Fri, 29 May 2020 22:44:18 +0100

With so much information out there today, having a system to process and manage them is crucial to not be overwhelmed. For me this involves having a good digital information capture and retrieval workflow, a.k.a note taking. I classify notes into three categories: micro text notes (<500 characters), notes consisting primarily text (including code), and notes that have embedded media like images. Micro text covers consists of fleeting thoughts and requires almost immediate offloading from the mind otherwise it will be forgotten. The latter two requires deliberate effort to plan and give structure to the content. Some software are better suited for one category than others, but the best will depend on one’s workflow. Last weekend, I reviewed my workflow and here are my reflections on all the software I’ve tried and used over the last decade in chronological order. Each section includes a verdict aimed at the reader thinking of using the software. Hopefully it is useful to curious readers looking for note taking software options.

Futurama Theorem

Sun, 09 Jun 2019 12:36:04 +0100

Futurama is a witty sci-fi cartoon series. It has made me silently exclaimed “that’s pretty smart!” on several occasions.

Season 7 episode 10, titled “The Prisoner of Bender”, outdone itself where it made me pause the video and try to solve the puzzle presented in that episode as if it was an online lecture. In that episode, the professor invented a mind-swapping machine and after using it on Amy and himself, they decided that they want to swap back. However, the machine can only be used on the same pair only once. The naive attempt of introducing a third party (bender) didn’t solve the problem either. How can they revert to the original state?

Kant Universality test

Sun, 10 Mar 2019 15:06:29 +0000

It is probably safe to say that as human beings, we all have some sense of what is right or wrong. The system through which we determine right or wrong conduct is called morality and the study of morality is called ethics. Hence we all subscribe to some form of morality, which could be taught by our parents or through our religion, and can be different. It is interesting to think about whether there is a “logical morality”, a morality where two rational beings can systematically decide whether something is right or wrong. When reading up on Kant recently, I learned about his formulation of a universality test, which seems to satisfy this “logical morality”.

Life and production possibility curve

Tue, 03 Jul 2018 09:14:57 +0100

In economics, the production possibility curve (PPC) reflects scarcity, choice and opportunity cost. Suppose there are two goods produced, the curve shows the combination of the two goods that can be produced when the resources are fully employed. The curve isn’t static - technological improvements can shift the curve outwards. A point below or on the curve represents the current state of production. A point outside of the curve indicates an impossible production state.

Council Tax Comparison

Mon, 07 May 2018 21:44:55 +0100

Introduction

Over a recent lunch conversation, I learned that council taxes in city of westminster borough is half that of lambeth. Finding it hard to believe, I did my own research and I was surprised by what I found!

This exercise involves looking up the values given by the council website, and then giving is a visual representation using a map of the borough. To start, I used this website to get a list of boroughs to consider.

Guide for choosing camera

Fri, 13 Apr 2018 22:33:04 +0000

Disclaimer: The following reflects my personal views only. Any misinformation is unintentional. Please feel free to provide feedback.

Introduction

My photography journey started just over a year ago, when I decided to get a [Sony HX90V]. Before that, I was using a [OnePlus One] for taking pictures. My main use of photography back then was documenting events in life, and the occasional travel photography.

I decided to get that camera when I started to find the quality of my travel photos a bit lacking. So I took the first step in understanding the tools needed to take nice photos.

Continuum hypothesis, a brief introduction

Wed, 30 Aug 2017 22:56:51 +0000

I haven’t had the need to read up on mathematical text for a long time. When I do find time to do so, I am usually impressed by the inexplicable beauty in the ideas presented. The following is my summary on the topic of set cardinality. I only assume that the reader understands elementary mathematical notation and vocabulary and nothing more.

Cardinality as an equivalence class

Back in school, we are told that |A| is the number of elements in A. This is fine until we start to think about the cardinalities of infinite sets. For example, the set of even numbers has the same cardinality as the set of natural numbers. Imagine someone coming up to you with a set and says, if you skip every other element in that set, you have a set with the same “size”. So size doesn’t mean much for infinite sets.

XOR curiosity

Sun, 13 Aug 2017 19:19:29 +0100

There is a formula for adding numbers from 1 to n and there is a notation for expression the product of numbers from 1 to n. But what about bitwise operations?

Let’s consider taking the bitwise AND from 1 to n.

We know that 1&2 = 0, and 0&x = 0 for all x. If we take the bitwise AND of numbers from 1 to n, we get the constant 0. That is not very interesting. Starting from some other number will also cause the series to eventually reach 0 and stay at 0.

Banksy's art

Sun, 18 Jun 2017 23:59:16 +0100

My first encounter with Banksy, the English Bristol-born graffiti artist, was back in 2012 when I visited Bristol and saw the hanging man. Back then I took a picture of the graffiti because it was provoking but I had no idea who the artist was.

Fast forward to 2015, I came across some artwork that had the distinct style of Banksy and read up more on him and his work. Banksy’s pieces usually have a social and political overtone and is usually very accessible to the public, without too much nuances or subtleties.

The ligher side

Sun, 28 May 2017 00:00:00 +0100

On one Friday evening, I went into this free concert performed by the San Francisco chamber orchestra not knowing what to expect. When I learned that it was about music humour I was pleasantly surprised. I didn’t even know there was such a thing.

The concert was something to titter over. I found myself giggling at times, not purely aided by the audience laughter, and I was curious why did the music evoke such a reaction. So naturally, I did some research afterwards to figure out what exactly makes music funny.

Custom firmware on Android

Tue, 13 Sep 2016 22:54:32 +0100

This article consist of an introduction of how I got my phone, a walkthrough of what I did to make my phone great again, and a brief discourse on security implications.

If you are unfamiliar with the terms below at any point in time, check out any generic rooting guide, like this one. They should cover most of the terminology.

Part one: getting the phone

It started when my one plus one (OPO) got sluggish after using it for two years. Expecting it to die soon, I began my search for a replacement phone.

Introducing Explosm RSS

Sun, 15 May 2016 09:55:20 +0800

Explosm rss feed

I occasionally enjoy the comics from http://explosm.net and I was annoyed that the RSS feed they provide requires the reader to click on the link in order to see the comic. The reason for using the RSS feed in the first place is to be able to get the updated content fast. Having to click a link and wait for the page to load just breaks that flow.

So I decided to take things into my own hand and write a RSS generator code here for the comic feed. The idea is simple, I parse the original RSS feed, extracting the link I need to press as a reader, fetch the link, parse the page and grab the comic in that page, create another feed with only that comic and expose this new RSS feed.

People just want to talk

Mon, 28 Mar 2016 09:55:20 +0800

You haven’t seen london until you’ve taken the night bus.

Adventures on the last train

It was Easter Sunday and I went over to a friend’s in the west for dinner (I stayed at Poplar, Zone 2 in east London). We played some board game afterwards and I planned to leave early enough so I don’t miss the last train. Despite leaving enough time to catch the penultimate train coming from heathrow, it didn’t arrive and I ended up waiting for close to 20 minutes for the last train.

Birthday paradox and music shuffling

Sun, 28 Feb 2016 09:55:20 +0800

Most music players have a shuffle mode so that songs don’t get played in the listed order. There are two ways this can happen: either pick a music at random after one song ends or pick the next song in some predetermined order. How do we tell if shuffle mode is doing one or the other?

There is a known problem or paradox known as the birthday paradox. In its popular variant, it asks what is the value of n such that in a room of n randomly chosen people, the probability that some pair of persons share the same birthday is > 50%. The shock comes when the number is not 365/2 but a mere 23 people. As a general rule of thumb, the number is approximately 1.2 * sqrt(n) for the probability to be > 50%. So now we can apply this to our music library and consider this thought experiment. Suppose songs are randomly chosen after one ends, and your library has 1000 songs, it would only take on average 38 songs before there is a repetition.

Random thoughts on Set, the game

Sat, 13 Feb 2016 09:55:20 +0800

Set, as a recreational problem

During Chinese New Year visiting, my cousin introduced the game set to me.

The objective of the game is to identify a set of three cards from 12 cards laid out on the table. Each card has 4 features, each with three variants. The four features are Colour, Symbol, Number, Shading. A set consists of three cards in which each feature is either the same on each card or different on each card. Examples and rules here.