Time Programming for Lawyers and Jurors

I often like to have streams of trials playing in the background when I am working, and the recent trial of interest was the trial of Karen Read, who was accused of murder. One issue in this case was a conflict between two timestamps logged by different apps on a potential suspect’s phone. Apple health had logged the person climbing flights of stairs at a given time, and at the same timestamp, a log from the app Waze indicated that the person was driving.

Five Nine Problems

A guilty pleasure of mine is the pursuit of perfection. It is certainly a vice in most contexts, but there are some problems whose solutions demand a measure of perfection. These are problems that I will refer to as “5-9 problems”: problems whose solutions need five 9’s (or more) in some dimension. Usually, those nines are correctness of some kind, but they can also be availability or for some systems, speed.

The Computer Architecture of AI (in 2024)

Over the last year, as a person with a hardware background, I have heard a lot of complaints about Nvidia’s dominance of the machine learning market and whether I can build chips to make the situation better. While the amount of money I would expect it to take is less than $7 trillion, hardware accelerating this wave of AI will be a very tough problem–much tougher than the last wave focused on CNNs–and there is a good reason that Nvidia has become the leader in this field with few competitors.

The Knight Capital Disaster

This account comes from several publicly available sources as well as accounts from insiders who worked at Knight Capital Group at the time of the issue. I am telling it second- or third-hand. On August 1, 2012, Knight Capital fell on its sword. It experienced a software glitch that literally bankrupted the company. Between 9:30 am and 10:15 am EST, the employees of Knight capital watched in disbelief and scrambled to figure out what went wrong as the company acquired massive long and short positions, largely concentrated in 154 stocks, totaling 397 million shares and $7.

Abstraction is Expensive

As you build a computer system, little things start to show up: maybe that database query is awkward for the feature you are building, or you find your server getting bogged down transferring gigabytes of data in hexadecimal ASCII, or your app translates itself to Japanese on the fly for hundreds of thousands of separate users. These are places where your abstractions are misaligned - your app would be quantitatively better if it had a better DB schema, a way to transfer binary data, or native internationalization for your Japanese users.

Contemplating Randomness

I have recently been immersed in the theory and practice of random number generation while working on Arbitrand, a new high-quality true random number generation service hosted in AWS. Because of that, I am starting a sequence of blog posts on randomness and random number generators. This post is the first of the sequence, and focuses what random number generators are and how to test them. Formally, random number generators are systems that produce a stream of bits (or numbers) with two properties:

Introduction to Micro-Optimization

A modern CPU is an incredible machine. It can execute many instructions at the same time, it can re-order instructions to ensure that memory accesses and dependency chains don’t impact performance too much, it contains hundreds of registers, and it has huge areas of silicon devoted to predicting which branches your code will take. However, if you have a tight loop and you are interested in optimizing the hell out of it, the same mechanisms that make your code run fast can make your job very difficult.

Rest in Peace, Optane

Intel’s Optane memory modules launched with a lot of fanfare in 2015, and were recently discontinued, in 2022, with similar fanfare. It was a sad day for me, a lover of abstraction-breaking technologies, but it was forseeable and understandable. At the time of Optane’s launch, a lot of us were excited about the idea of having a new storage tier, sitting between DRAM and flash. It was announced as having DRAM endurance and speed with the persistence and size of flash.

Use One Big Server

A lot of ink is spent on the “monoliths vs. microservices” debate, but the real issue behind this debate is about whether distributed system architecture is worth the developer time and cost overheads. By thinking about the real operational considerations of our systems, we can get some insight into whether we actually need distributed systems for most things. We have all gotten so familiar with virtualization and abstractions between our software and the servers that run it.

The Most Useful Statistical Test You Didn't Learn in School

In performance work, you will often find many distributions that are weirdly shaped: fat-tailed distributions, distributions with a hard lower bound at a non-zero number, and distributions that are just plain odd. Particularly when you look at latency distributions, it is extremely common for the 99th percentile to be a lot further from the mean than the 1st percentile. These sorts of asymmetric fat-tailed distributions come with the business. Often times, when performance engineers need to be scientific about their work, they will take samples of these distributions, and put them into into a $t$-test to get a $p$-value for the significance of their improvements.