Daniel Lemire
Computer science professor who works on fast data processing; co-author of the simdjson parser and a weekly blogger about software performance since 2004.
Daniel Lemire did not write this page. ppll compiled it from their own words, each linked to the source. Is this you? · Report a mistake
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What they believe
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Academic publishing functions mainly to sort people for jobs rather than to produce useful knowledge.
The purpose of the academic output is to sort people out for jobs.
lemire.meSaid 20 Sept 2026This on korrents
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CPU performance keeps improving quickly rather than stagnating.
In effect, what I am demonstrating is that CPUs are not boring. They are improving fast.
lemire.meSaid 19 Sept 2026This on korrents
The bold line is korrents’ wording; the quote is theirs. These 2: what they wrote before what they said aloud, one per source, newest first.
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- x.com
- BlogWebSocket servers in JavaScript: Node.js, Bun and Deno in 2026
- GitHubNew repolemirecodechat
+ 1 more
- GitHubjswebsocket_bench
9 October
- GitHublemirecut — Daniel Lemire's video tools
- x.com
- x.com
8 October
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4 October
1 October
30 September
28 September
26 September
25 September
21 September
Nothing matches.
Beliefs
Korrents What they believe 13 beliefs — each backed by an exact quote.
Each is a — compiled by korrents.com, not by them: the one-line wordings are korrents', the quotes are theirs.
Recent
Academic publishing functions mainly to sort people for jobs rather than to produce useful knowledge.
The purpose of the academic output is to sort people out for jobs.
AI is breaking the academic sorting machine Said 20 Sept 2026
Most people who complete a PhD today will not land a tenure-track or tenured position, and the odds keep shrinking.
If you hold a PhD today, your chance of having a tenure-track or tenured position is about 10% and falling.
AI is breaking the academic sorting machine Said 20 Sept 2026
Scientific and academic evaluation will shift away from published papers as the measure of output, toward valuing real-world results.
I predict that, over time, the focus will move away from "papers as the final output."
AI is breaking the academic sorting machine Said 20 Sept 2026
Show 10 more
CPU performance keeps improving quickly rather than stagnating.
In effect, what I am demonstrating is that CPUs are not boring. They are improving fast.
How did Apple Silicon get 50% faster in three years? Said 19 Sept 2026
The SSE4.2 string-comparison instructions on x86 are slow compared to alternatives.
NEON has nothing like it; on x64, the closest thing is the SSE4.2 string-comparison instructions (pcmpistrm), which are slow.
Faster JSON parsing with SVE2 on ARM processors Said 18 Sept 2026
C++23's std::flat_map is a better choice than std::map for many practical use cases.
In many practical cases, the new std::flat_map is a better alternative to the std::map.
How fast is C++23’s std::flat_map? Said 16 Sept 2026
Subnormal floating-point numbers remain a real performance cost on Intel processors, but not on AMD or ARM processors.
Thus it appears that on the latest AMD and ARM processors subnormals might not be a concern. But they remain very much a performance issue under Intel processors.
Subnormal floating-point numbers are expensive… on Intel processors Said 15 Sept 2026
Professionals across many fields will adapt to working with AI, and that shift cannot be reversed.
Mathematicians, software developers, engineers, lawyers, physicians will all learn to work with AI. You cannot put the genie back in the bottle.
The four-colour theorem was only the start Said 11 Sept 2026
AI will increasingly produce mathematical proofs, just as it already writes most code.
Difficult proofs will now be built with AI, just as most code will be written with AI.
The four-colour theorem was only the start Said 11 Sept 2026
Mathematicians who continue working without AI should be seen as practicing an art form rather than research.
People who insist on pen and paper should view themselves as artists.
The four-colour theorem was only the start Said 11 Sept 2026
Less technology and less wealth increase the risk of human extinction, rather than reduce it.
In fact, the risk of human extinction is assuredly higher if we are poorer and have less technology.
Fear Is Not an Argument Said 10 Sept 2026
People who believe AI poses an existential risk tend to hold a totalitarian ideology that requires universal agreement to work.
These people tend to carry a totalitarian ideology. Their ideas will only work if everyone is made to agree.
Fear Is Not an Argument Said 10 Sept 2026
Publicly expressing fear of AI can function as virtue signaling rather than genuine concern.
Expressing fear of AI can become a form of virtue signaling.
Fear Is Not an Argument Said 10 Sept 2026
What is a korrent?
A korrent is a belief a person has stated in their own words: one sentence stating the claim, backed by a quote and a source, kept at korrents.com.
Under a name here, the quoted block is what they actually said. The korrent beneath it is the claim those words support, in korrents' wording — tap it to see the record, its source, and who else holds it.
Nobody here wrote their own korrents. They are compiled from public statements, and a person can change their mind, which is recorded too.
Recommends rcmnd
rcmnd What they recommend 15 things — each backed by an exact quote.
Compiled by rcmnd.app, not by them: the quotes are theirs, and each links to the post it was copied from.
Recent
Loved Theft of Fire
Theft of Fire offers a plausible and realistic universe. The characters, Marcus Warnoc and Miranda Foxgrove, are not mere archetypes; they are complex, flawed, and deeply human. Their struggle to trust one another and overcome their own demons is a powerful allegory for the modern human condition.
lemire.me 24 Feb 2024
sponsored
Recommends Template Metaprogramming with C++
I spent the last few weeks reading Template Metaprogramming with C++ by Marius Băncilă. It is currently 50$ on Amazon. Though, technically, the book is about advanced 'template' techniques, it is much more broad and practical. It is one of the 'good programming books'. If you are an experienced C++ programmer, you should give it a peek
lemire.me 26 Oct 2022
sponsored
Loved How Innovation Works
I read How Innovation Works by Matt Ridley in a few hours. It is a delicious book.
lemire.me 5 Jun 2020
Show 12 more
Liked FormulatePro
To sign forms electronically, I have been using something called FormulatePro. It gets the job done.
usesthis.com 5 Nov 2013
Loved iPad 4
I mostly use my iPad however: I was an early iPad adopter and I have since upgraded to the iPad 4. I am very pleased.
usesthis.com 5 Nov 2013
Uses Omnigraffle
When I need to draw diagrams, I use Omnigraffle.
usesthis.com 5 Nov 2013
Liked Prezi
When I give presentations, I like to use Prezi.
usesthis.com 5 Nov 2013
Uses Ubuntu
I use an Ubuntu distro for Linux, mostly because it is the most popular option.
usesthis.com 5 Nov 2013
Uses Vim
When I connect to a Linux box, I use vim as a text editor. For various reasons, I tend to write a lot of my software in vim.
usesthis.com 5 Nov 2013
Uses Texpad
For web browsing, I use Google Chrome. As a LaTeX editor, I use Texpad.
usesthis.com 5 Nov 2013
Uses Eclipse
However, most of my C++ and Java hacking is done using an older version of Eclipse.
usesthis.com 5 Nov 2013
Mixed on Smultron
On my Macs, I use Smultron as a text editor when I am not in a bash shell, despite the fact that it is buggy.
usesthis.com 5 Nov 2013
Uses Fresh Roast SR500
I do drink a massive amount of coffee however. I roast my own coffee with a Fresh Roast SR500.
usesthis.com 5 Nov 2013
Mixed on Statistical Analysis with R
The book is colorful and ludic which is a good idea for a "Beginner's Guide". The layout is attractive, there are many detailed examples. I like the pedagogy: the author wants you to learn by doing. However, the book is poor as a reference: the coverage is limited despite the 300 pages and the chapter summaries are strictly non-technical.
lemire.me 19 Jan 2011
sponsored
Liked Spin
The novel is very good. The author writes with good scientific rigour. The writing is supported by repeatedly introducing new mysteries in every chapter... to keep you coming for more. The characters are believable and well drawn.
lemire.me 17 Nov 2008
Where they publish
Site lemire.me Personal homepage.
Link verified 5 Sept 2026.
Blog Daniel Lemire’s blog Weekly posts on performance and computer science.
Recent
- Decoding base64 in Python at 10 gigabytes per second 17 Oct 2026 We sometimes need to convert binary data to text. For example, your emails must be stored as text files. Naïvely, you could just use a string of 0 and 1, but it would mean using one character per bit. We can do better b…
- Redis now has compressed bitmaps (Roaring) 15 Oct 2026 Redis is an in-memory database. Salvatore Sanfilippo started it in 2009, and it is now one of the most widely deployed pieces of server software. It is often used as a cache in front of a slower database. You talk to it…
- Parsing JSON at tens of gigabytes per second… in Python 12 Oct 2026 Python used to have limited parallelism, due to its global interpreter lock (GIL). Only one thread could run Python code at a time. Python 3.14 comes in a free-threaded version (python3.14t), without the global interpre…
Show 17 more
- WebSocket servers in JavaScript: Node.js, Bun and Deno in 2026 10 Oct 2026 WebSocket is a standard protocol to hook up a client and a server in a persistent manner. It is commonly used for live chat, notifications, multiplayer games, collaborative editing, and streaming dashboards. Many server…
- Faster Python startup with lazy imports 9 Oct 2026 When a Python program starts, it needs to load all its dependencies (import). With the upcoming version of Python, it is possible to use lazy imports instead. lazy import json lazy from decimal import Decimal In this in…
- Mastering SIMD with Java Vector API 7 Oct 2026 I write a lot about data parallelism. About how our processors have special instructions that can do several operations at once. They are often critical to get the best performance out of a CPU. Compilers are sometimes…
- Faster software linking with mold 6 Oct 2026 When you build a program, the compiler turns each source file into an object file. Then a linker stitches all the object files and libraries into one executable. On Linux, the default linker is usually GNU ld (also call…
- Ephemeral testing 5 Oct 2026 We have many ways to ensure software quality. Unit testing. Fuzz testing. Integration testing. And so forth. I’d like to propose a method that was unthinkable before: ephemeral testing. (Ephemeral is a fancy word for ‘t…
- Research paper overload: submissions capped at two a month 4 Oct 2026 Much of my research is on arXiv. I was one of the early adopters. It is simply a repository of research papers with PDF and metadata. It makes it convenient to find research without any paywall. Physicists started it in…
- Google’s first orbital data center is in orbit 4 Oct 2026 (October 1st). They say it is about the size of a fridge. It has one kilowatt of solar power. It is about the power of a household. It was launched on a Falcon 9 rocket (SpaceX). It should run for about a year. Google p…
- Parsing compressed JSON at 40 GB/s 1 Oct 2026 A common way to store JSON data is to write one document per line. We call it NDJSON or JSON Lines. Log files, database exports and machine-learning datasets often come in this format. The files can be large, so we may…
- Transcoding UTF-8 to UTF-16 with replacement at gigabytes per second 30 Sept 2026 Our software represents strings using the UTF-16 or the UTF-8 formats. Most text on the web is UTF-8, but Java, C# or JavaScript represents the strings as UTF-16 to the programmer. Sometimes we need to transcode (conver…
- How do you deal with people who strongly disagree with your views? 30 Sept 2026 1. Begin by genuinely listening to them. Make sure that you understand them. It is often useful to ask for confirmation: restate what you think they are saying and make sure that you understand. Physically, it helps to…
- simdjson 5.0 is out 28 Sept 2026 The simdjson library is a C++ library to parse and generate JSON. It is used in Node.js, ClickHouse, Meta Velox, StarRocks, Apache Doris, the Ladybird browser and many other systems. We released version 4.0 a year ago,…
- How fast can you fix a UTF-16 string in C#? 26 Sept 2026 C# strings are UTF-16. Most characters are one 16-bit code unit. Characters outside the basic multilingual plane, emoji included, take two: a high surrogate (U+D800 to U+DBFF) followed by a low surrogate (U+DC00 to U+DF…
- A thesis isn’t enough for a PhD 26 Sept 2026 To get a PhD, you typically have to enroll in a graduate program. Then you complete a few relatively easy courses. You might need to pass a comprehensive examination that checks whether you have a basic understanding of…
- How many strings can you create per second? 25 Sept 2026 We create new strings all the time. How quickly can you produce short strings in your programming languge? To create a meaningful string, we convert an integer to a string. In Python, that is str(i). The loop stores eac…
- If you don’t have the factories, you lose the expertise 24 Sept 2026 Mainstream economists have been advocating for the marvellous effects of global trade for decades. Who needs these factory jobs anyway? We’ll be designing the robots and the nuclear rockets. Except that, no. It does not…
- A summer of AI optimization 22 Sept 2026 I maintain and comaintain several open-source libraries. Some of them are widely used: ada parses URLs in Node.js, fast_float parses numbers in GCC’s standard library and in Chromium, simdjson parses JSON in Node.js, si…
- The data does not show mass unemployment 21 Sept 2026 If AI is causing mass unemployment among software developers, it is not showing up in the data yet. The USA had more software developers as a percentage of the population in 2025 than in 2021. On average salaries are sl…
Link verified 5 Sept 2026. Recent items update automatically from the channel.
x.com @lemire His X account.
Recent
- What do you do if someone offends you? Adult human beings tend to be pretty good at the right answer: do not react. At least at first. For a tribe or a civilization, this non-reaction is obviously useful. Fighting is expensive for the group and best be avoided. But it is also often the best strategy for the individual. For three main reasons: 1. We are frequently wrong about what happened. Sometimes people are just careless. Or there is a misunderstanding that can be resolved. It happens often enough. 2. Provocations often see to extract status. Someone who offends might want to establish the… 17 Oct 2026 youtube.com
- We often convert binary data to base64 (crypto, images). The Python standard library is ridiculously slow. Thankfully, you can just use the fastpybase64 module and get crazy speeds... See my article for details. 17 Oct 2026
- @esrtweet quotes Voltaire... let me refer to the full quote... « Formerly there were people who said: “You believe incomprehensible, contradictory, and impossible things because we have ordered you to; therefore do unjust things because we order you to.” Those people reasoned admirably. Certainly, whoever has the power to make you absurd has the power to make you unjust. » I want you to pause and think about your life thus far. Does it apply to any of it? Voltaire was not taking an atheistic stance. He was criticizing unmoored authority. Voltaire really hated the Catholic Church for how it ab… 17 Oct 2026
Show 17 more
- The next Redis release should have native support for Roaring bitmaps. I ran some benchmarks. In some instances, this could drastically improve your performance. This could similarly be added to Valkey soon if people want, there is an issue and code proposal. Check my article for more details. (Such as 'what are Roaring bitmaps?') 16 Oct 2026
- Competition ! Meta just came out with a competitive coding agent, Muse Wonder Full. You can subscribe for either 50$/month or 200$/month. For coding, 'Muse Wonder Full' seems to be a match for the best models from Anthropic and others. 14 Oct 2026
- Do you trust Claude Code or Grok to run on your machine? How do you know it won't email all your secrets to your girlfriend? Microsoft cam up with a solution: Microsoft Execution Containers (MXC) . The idea is simple. You write a policy, a JSON file that says which files the program may read, which files it may write, and whether it may use the network. It is not a bad idea. However, on my macBook, I find that MXC can add significant overhead. I measure over 10 ms in startup cost. It gets worse if you run a command like git which seeks to access a temporary directory that you did not allow. T… 13 Oct 2026
- Thanks to everyone who gave me ideas as what to talk about regarding AI and programming in my upcoming lecture. I will try to give credit. 12 Oct 2026
- With Python 3.14, you can use actual threads in a single Python process... which makes it possible to parse JSON (for example) at insane speeds. See article for details. 12 Oct 2026
- I am giving a talk on AI and programming in a couple of weeks. I have an abstract but the talk is not ready yet. What should I talk about? The audience will be made of young people. 11 Oct 2026
- Possibly due to the high cost of hardware, we are selling fewer PCs. 11 Oct 2026
- Back in 2023, I compared the three main JavaScript runtimes (Node, Bun, Deno) on a WebSocket benchmark. I have redone the benchmark with a better methodology (had my AI write a client in C). Surprisingly to me, I find that Node.js really does well. Deno : not so much. Details in the article. 10 Oct 2026
- OpenAI expects $70 billion in revenue in 2026. That would exceed IBM. 9 Oct 2026
- Time to be lazy! Python scripts can take a long time start. They need to load all their modules... In the upcoming Python release, you can make your scripts much faster with lazy module loading. 9 Oct 2026
- This is a representation of what an orbital data center might look like. It stays close to the surface of the Earth, and it can always face the Sun. 8 Oct 2026
- If you are an engineer who builds actual software and you'd like to review a research paper from time to time, please sent me a note in X chat. You *DO NOT* need to have a PhD. But, ideally, you should sometimes enjoy reading a research paper. Give me a description of your interests. I am an editor for Software: Practice and Experience. I filter papers that I send to review, but I often run out of people with actual experience. I have a few names, but they get exhausted after a time. Yes, I know I could just ask Claude to review the papers... and it does a fair job... But what I care about is… 8 Oct 2026
- There is much talk about 'AI cloning'. You take an existing piece of software, and you build your own version... using AI as a helper. It is amusing, but it is akin to using the newly invented radio to broadcast theatre plays. I am not sure that kids in the future will want to learn Photoshop. We shall need software forever... but do we need *this* particular kind of software? It seems almost certain to me that what will eat into Adobe's margins won't be a AI clone of their software. And to be clear, I think that such clones will, eventually, work quite well. Don't be too quick to judge them… 8 Oct 2026
- Find bugs in our fast URL parser and get rewarded! This URL parser is used everywhere in critical code. C++ 7 Oct 2026
- I write a lot about data parallelism. About how our processors have special instructions that can do several operations at once. They are often critical to get the best performance out of a CPU. Compilers are sometimes able to take advantage of these instructions. But it is hard to tell when it will work. For Java programmers, you can write directly for data parallelism since JDK 16. With enough skill, you might multiply the performance of a few key functions. The Vector API is in the incubator module jdk.incubator.vector. It still not officially supported, but you can enable it by passing --… 7 Oct 2026
- The version 5.0 of simdjson is on godbolt so you can check the assembly output of this C++26 code. Link: 6 Oct 2026
- When building software, like Node.js, you need to both compile and link your software. The faster, the better. Amazingly, you can replace the default linker under Linux with something much faster: mold by @rui314 Check my article for details. 6 Oct 2026
Link verified 5 Sept 2026. Recent items update automatically from the channel.
GitHub @lemire simdjson and other performance libraries.
Recent
- talks — Random material having to do with Daniel Lemire's talks 21 Oct 2026
- simdsearch 17 Oct 2026
- Code-used-on-Daniel-Lemire-s-blog — This is a repository for the code posted on my blog 17 Oct 2026
Show 9 more
- New repolemirecodechat 10 Oct 2026
- jswebsocket_bench 10 Oct 2026
- lemirecut — Daniel Lemire's video tools 9 Oct 2026
- docker_programming_station — Simple scripts for programmers who want to work within Docker 1 Oct 2026
- spyhunter — Spy Hunter 26 Sept 2026
- valigo 25 Sept 2026
- testingRNG — Testing common random-number generators (RNG) 21 Sept 2026
- fastconstmap — Fast, immutable, compact map from strings to 64-bit integers — for Python. 17 Sept 2026
- rsconstmap — A static map from strings to u64 values using binary fuse filter construction. It can be several times smaller and faster than the equivalent HashMap. 17 Sept 2026
Link verified 5 Sept 2026. Recent items update automatically from the channel.
About the English under a post
Some people here publish in a language other than English. Where they do, this site shows a machine translation beneath the post, in this typeface — the site's own, not theirs.
The post itself is never changed, moved or hidden: what is set in the serif above is exactly what the person published, and it is what to quote them on. A translation can be wrong in ways that matter, especially about tone.
Only the post's own words are translated. A quoted post, a linked article and a belief on korrents.com are left in their original language.