This is the blog of Vivek Haldar

When to do a rewrite

Spolsky’s famous screed against rewriting from scratch is now canonical. All the same, there are valid reasons to do a rewrite:

  • Your understanding of the domain, or the domain itself, has changed drastically in the process of building the first version.
  • The scale for which you built the initial system has grown by more than an order of magnitude. The right design for millions of users is very different than that for thousands.
  • Newer languages and runtimes make the product much better along some dimension: deliver better performance, be more maintainable etc.
  • You have accumulated so much technical debt that starting from scratch is easier than untangling the mess you have. This is often the most misleading reason, because engineers always prefer a system they wrote from scratch to inheriting one which works just fine. But even so, it does happen.

None of the above takes away from what Spolsky wrote. A rewrite is still a risky endeavor, even if one or more of the above conditions hold true, and should always be approached with caution and humility.

His argument was much stronger in the era of software that was shrink-wrapped to PCs, because the slow rate of change of the surrounding environment made many of the above reasons inapplicable.

But server-side software that powers online services is always in a constant state of flux. There is rarely any concept of “done”. The product might look more or less the same from the outside, while the backend code constantly churns to deal with growing scale, new stacks, and other services it depends on.

Learning your life

If you are a “regular” person living and working in modern civilization, it is likely that your life has a few recurring patterns:

  • on weekdays, you travel from home to work in the morning, and back in the evening; perhaps punctuated with a school or daycare drop-off and pick-up.
  • on weekends, you either mostly stay at home or frequent a small set of haunts (beaches, restaurants etc).
  • infrequently, you break out of this pattern by leaving the orbit of work-home to go on a vacation.

This is easy to figure out by observing someone for a short period of time. Of course, your phone already does this.

The above model of your life could be described in a few kilobytes. It is a zeroth-order machine learning problem. Is that depressing? Does that mean your whole life has a few kilobytes worth of complexity?

John Foreman, in his poignantly named piece “Data Privacy, Machine Learning and the Destruction of Mysterious Humanity”, takes a view of the field from the inside, and it sounds like that of a physicist working on the Manhattan Project worrying about the impact of what they’re building.

Our past data betrays our future actions, and rather than put us in a police state, corporations have realized that if they say just the right thing, we’ll put the chains on ourselves… Yet this loss of our internal selves to the control of another is the promise of AI in the hands of the private sector. In the hands of machine learning models, we become nothing more than a ball of probabilistic mechanisms to be manipulated with carefully designed inputs that lead to anticipated outputs… The promise of better machine learning is not to bring machines up to the level of humans but to bring humans down to the level of machines.

That is a dim, if plausible, view.

It is based on a pessimistic view of humans as always giving in to nudges to behave as our worst selves. I hope that we are better than that. We are already surrounded by advertising for junk food, and yet a substantial fraction of us manage to ignore that and eat healthy. I hope machine predictions that try to nudge us face a similar fate: predictions that look down on us will be indistinguishable from low-quality ones. The quality and tone of predictions will become an important part of the brand identity of the company emitting them. Do you really want to be the company known for peddling fatty, salty food, legal addictive substances, and predatory loans?

A tangential point: naming matters. Statistical inference, which is what machine learning really is, is a less scary name. “Statistical inference” conjures images of bean-counters with taped glasses; “machine learning” of an inevitable army of terminators.

Circling back to the question I posed above: is your life really describable in a few kilobytes in a predictive model? No. A model is a probabilistic abstraction. You, and your life, are not a sequence of probabilities, in much the same way that hiking a trail is a much richer, “realer” experience than tracing your way through a detailed trail map.

“The AP announced last month that it would use Automated Insights’ software, called Wordsmith, to produce up to 4,440 robot-written corporate-earnings reports per quarter, more than ten times the number its human reporters currently produce. When Alcoa’s earnings report hit the wire that day, the data was instantly compiled by a firm called Zacks Investment Research and passed through the AP’s proprietary algorithm, which pulled out key numbers and phrases and matched them against other contextual information. In milliseconds, the software produced a full story written in AP style, indistinguishable from one made with human hands. In short order, the story appeared on many AP member sites.”

Robot Journalism

“Here’s the tablet news app I’m hoping for in 2014: something that detects when I’m lying down in bed (it knows my device orientation and, using the ambient light sensor, can detect it’s dark) and serves me the sort of video content that I never have time to watch during the day.”

Katie Zhu

Garland Words

I define a garland word to be one which can be formed by chopping off the last few letters and “wrapping around” to the start.

For example: You can chop off the the trailing “on” from “onion” and still form the word by wrapping around to the starting “on”. In other words, you can write the letters “o”, “n”, “i” in a circle, in that order, and form the word “onion”.

I say that a garland word is of degree n if you can do the above with the last n letters of the word.

It turns out that garland words are fairly rare. In the English dictionary that came installed on my Ubuntu machine, there were 99171 words, only 199 words were garland words of degree 2 or above. The highest garland degree was 4.

The exact distribution was: there were only 3 words of degree 4, 32 of degree 3, and 164 of degree 2.

The degree 4 garland words were: “hotshots”, “beriberi” and “abracadabra”.

Lurking Smalltalk

Stephen Kell’s paper at PLOS 2013 meditates on one of CS’ oldest design questions: what should be in the operating system, and what in the programming language and runtime? The paper was a breath of fresh air; one of those opinionated design thinking papers that one rarely sees in academic CS venues. Do read the whole thing.

This question comes into stark relief if you look at what a modern language or VM runtime does: among other things, it multiplexes resources, and protect access to them. But that’s also exactly what the OS is supposed to do!

The paper riffs on an earlier idea from Dan Ingalls: “An operating system is a collection of things that don’t fit into a language. There shouldn’t be one.” The central problem tackled in the paper is that of having more generic object bindings in the OS, as opposed to the “static” filesystem bindings for most operations. Kell uses the following example:

Suppose we wish to search some object for text matching a pattern. If the object is a directory tree of text files, grep -r does exactly that. But suppose instead our directory tree contains a mixture of zipped and non-zipped files, or is actually some non-directory collection of text-searchable objects, such as a mailbox. In Smalltalk parlance, how can we make these diverse objects “understand” (via a collection of interposed objects) the messages of our grep -r (and vice versa)?

This would indeed be elegant. But I’m afraid the engineer in me isn’t terribly excited by that.

“All problems in computer science can be solved by another level of indirection” is a famous quote in computer science. The next sentence is much lesser known: “But that usually will create another problem.” What Kell is proposing adds flexibility in binding by introducing indirection.

Indirection is controlled by some sort of configuration the binds each side of it. And configuration implies a lot of added complexity. The UNIX model of “everything is a stream of bytes and can be treated like a file” might be simple and unstructured, but that is precisely what enabled a multitude of structure to be built on top of it.


It’s commencement—and commencement speech—season. The one that’s been on my mind the most this year has been Paul Ford’s speech to a graduating class of interaction designers. His unifying thread is our conception of time:

The only unit of time that matters is heartbeats. Even if the world were totally silent, even in a dark room covered in five layers of foam, you’d be able to count your own heartbeats.

When you get on a plane and travel you go 15 heartbeats per mile. That is, in the time it takes to travel a mile in flight your heart beats 15 times. On a train your heart might beat 250 times per mile…

… If we are going to ask people, in the form of our products, in the form of the things we make, to spend their heartbeats—if we are going to ask them to spend their heartbeats on us, on our ideas, how can we be sure, far more sure than we are now, that they spend those heartbeats wisely?

Turns out, heartbeats are a great unit of time for another reason: all animals have approximately the same number of heartbeats in a lifetime.

With each increase in animal size there is a slowing of the pace of life. A shrew’s heart beats 1,000 times a minute, a human’s 70 times, and an elephant heart beats only 28 times a minute. The lifespans are proportional; shrew life is intense but brief, elephant life long and contemplative. Each animal, independent of size, gets about a billion heartbeats per life.

I find that deeply poetic.

The biggest winners may be lawyers who can use machine intelligence to create an automated large-scale practice. The Walton family, it’s worth recalling, got rich by effectively automating large-scale retail. More generally, there may be jobs for a new category of engineer-lawyers—those who can program machines to create legal value.

But the large number of journeyman lawyers—such as those who do routine wills, vet house closings, write standard contracts, or review documents on a contractual basis—face a bleak future.

Machines v. Lawyers, by John O. McGinnis

“Autodesk’s automated design software works through three layers. Generators populate physical space with matter, creating thousands of design suggestions in a split-second. Analyzers test each design against constraints developed by the designer: does it fit in the desired shape? Does it satisfy strength, thermal, material, and mechanical requirements? Above those, an optimization system finds the best designs, returns them to the starting point, and refines them repeatedly.”

The Automation of Design

The Eames house was everything I wanted: modern, but lived in, made out of everyday, accessible materials. No pristine white, dustless Dwell magazine show rooms here. There are plants and books and lights and seats and dust and you get the feeling it is a beautiful, functional space. There are finger prints all over it. The more I click around the web, the less and less I sense those fingerprints on people’s websites the way I used to. I’m not sure if it’s because of templates, or because those things take time, or if people just don’t think it’s worth it. But I think those traces of people are worth the effort, so I wanted to really work towards having this site feel like it was made by a person, and not some smug guy in a very tight, black turtle neck. Has anyone ever smiled in Dwell?

I wanted something homey. Better yet: homely. Americans think of homely as something that’s unhandsome, maybe even ugly. But the Brits observe the root “home,” since they invented the damn language. Homely, for them, is like a house: familiar, comforting, easy. There’s a rightness to it. For me, the Eames house is homely, because they filled it to the gills with the things they loved. How great would it be to have that online, where you would not run out of shelves? It’s an old dream, and one that’s still alive, but we’ve outsourced it. I think that shelf belongs at home.

Frank Chimero, on the design of his new site

Why technologists want to secede

Tech’s secessionist streak has recently got a lot of attention. Balaji Srinivasan thinks we should build a new society based on technology, breaking free from the “legacy” institutions we’re currently hobbled with. Larry Page hopes for experimental societies where change and experimentation can proceed much faster. Elon Musk wants to go live on Mars.

Most reactions to this have been along the lines of “look at these rich powerful elites thinking they can up and leave and do without all the rest of us!” I want to focus not on the politics behind this, but the motivation.

These ideas are getting attention now because rich and powerful titans of tech are espousing them. But these are the secret fantasies of every geek, rich or not, powerful or not.

Geeks have deep isolationist tendencies. They prefer losing themselves in sci-fi worlds to hanging out with friends. They build an early affinity with machines and programs. They sense that programming is the ultimate in world-building, and what’s more, it’s executable! They build elaborate towers of abstraction. They are drunk on the clean rationality of the world that the machine and they have built and understand.

Eventually, they secretly wish for a more ordered world. A world that is not messy or unpredictable. A world where one might have to work hard to establish the priors, but once they are, everything follows.

It is telling that one of the central activities in programming is abstraction. Abstraction is nothing but taking a jumble of intricate detail, putting it in a tightly sealed box, and then poking very small, well-defined holes in the box to interact with that jumble. So clean! So much better!

But every abstraction is leaky. Ints carry the baggage of their bit-width. In a perfect world, every int would be a BigInt with unlimited range. But we live in a world where it matters whether ints fit in a hardware register or not. Networks carry the baggage of not being perfect links. In a perfect world, a link between two machines would be an immutable, always-available channel for sending messages between them. But we live in a world where wires break.

This is the central tension in the mind of every geek. The constant need to abstract, to order, to rationalize, pitted against the necessary realization the world and entropy will eventually thwart you.

Secession is simply the same need for order and abstraction carried into the geek’s mental model for society.

I wrote previously:

The world of humans is messy, unpredictable, and—this is the part that infuriates you the most, the part you simply don’t get, the part that will forever make you an outsider—unreasonable. Humans are unreasonable. Your whole life, you’ve trusted one thing to save you. And saved you it has, again and again, without fail. That one thing is reason. Computers are a tool of reason, to be handled by people who obey the code of reason. People who are involved with computers, they’re reasonable, just like you. You all share a deep, unspoken bond. You’re all worshipers in the church of reason.

Please don’t hold that against us.

What advice would you give to someone starting out?

"You have to be prepared to give creative work 150%. I hear a lot of young people talking about life/work balance, which I think is great when you’re in your 30s. If you’re in your 20s and already talking about that, I don’t think you will achieve your goals. If you really want to build a powerful career, and make an impact, then you have to be prepared to put in blood, sweat, and tears. I don’t think everybody is willing to do that, but if you have the opportunity to do so, you should. That’s why many people go to graduate school in their late 20s: it forces them to devote intense time and focus to their work. It’s an experience that will change you forever."

Ellen Lupton, interviewed by Tina Essmaker.

Bleeding buffers

A lot has been written about Heartbleed. Here are my two cents.

The problem is that all our modern computing infrastructure is written in a language, C, that was designed to be a thin layer over assembly and hence has no memory safety. A memory-safe language, which is to say, any modern post-C/C++ language, still allows writing buggy code that can be exploited—for example, look at the raft of SQL injection attacks in Java backends—but the bar for exploitation is much higher and the space of possible attacks much smaller when an attacker can’t turn array dereferences into a way to read and write arbitrary memory addresses.

Type and memory safe languages have existed for a while now. Language based security and static analysis is still a thriving research area, but it is also mature enough that a broad set of results and techniques have been found to be generally useful, many of which have even made it into mainstream languages and tools. Why then are we still in this state?

The two immediate answers that come to mind—improving the safety of C/C++, and writing infrastructure in safe languages—are, upon closer inspection,riddled with complexities.

Making C/C++ memory safe is possible, but it is not as simple as flipping a switch. There is a price to be paid in performance, of course, but even if one were willing to pay that, there might be scores of subtle behavior changes in code made safe this way. There is probably tons of code out there that depends on unsafe behavior.

Writing SSL in a safe(r) language is possible. But everything that would want to link it (browsers and web servers) is written in C. One could use cross-language calling facilities, but that is rarely clean due to impedance mismatches, and of course, that still leaves the calling code memory-unsafe. You’d have to rewrite all the net’s critical infrastructure in a safe language and runtime. That’s wishful thinking.

When physical infrastructure decays it is visible. A new road uses the latest knowledge and practices for building roads, not those from thirty years ago. Neither is the case for our computing and network infrastructure.

In a strange inversion of the commonly held belief that hardware is hard to change and software is easily changed, some burden for safety might eventually fall on the processor. One example was when CPUs started supporting the no-execute bit to prevent code injection attacks. I wouldn’t be surprised to see more hardware features along those lines.

Relevant links:

You can’t run with the machines

I recently read “The Second Machine Age” by Erik Brynjolfsson and Andrew McAfee. The major points the book makes—that information technology and digitization is exponential, that automation is rapidly expanding into even cognitive tasks that until recently were thought doable only by humans, that the digital worldwide economy rewards winners and leaves even close seconds in the dust—are all quite well-known by now, but the authors have tied them together with a narrative that makes the book a good single place to read about them.

I particularly looked forward to the chapter titled “Racing With The Machines: Recommendations for Individuals”, in which they suggest what kind of work will be left for humans to do, and what skills we should try and develop to stay ahead of automation. I really wanted to know if they had cracked the nut of how we would stay gainfully employed. I was disappointed.

The the authors looked at prior attempts by Levy and Murnane that tried to predict limits on what activities would still require humans. They said that computers are good at following rules and bad at pattern-recognition, giving the example of driving a car as being too cognitively and sensorially complex to be automated. As the authors say in the book: “so much for that distinction.” Then they go right ahead and make their own prediction of the next frontier that computers will be unable to cross:

Our recommendations about how people can remain valuable knowledge workers in the new machine age are straightforward: work to improve the skills of ideation, large-frame pattern recognition, and complex communication instead of just the three Rs. And whenever possible, take advantage of self-organizing learning environments, which have a track record of developing these skills in people.

The biggest problem with this advice is that it is skating to where the puck is, not where it is going to be.

The example they lean on the most is freestyle chess where teams of humans and chess programs compete against each other (hence the title of the chapter). It turns out that the combination of a chess program guided by a human is more powerful than either alone. Freestyle chess is also a central example in Tyler Cowen’s latest book. Unlike Brynjolfsson and McAfee, Cowen wonders if this is just a transitional phase, and if humans will ultimately not add any value in this pairing.

Their recommendation about “ideation” and “large-frame pattern recognition” is not concrete enough. What does that mean specifically for someone choosing a college major today? And more importantly, can we be sure that those activities will remain out of the reach of computers by the time they graduate?

The debate about whether human thought is computable is an open one, but the vast majority of human cognitive activity does not happen anywhere near that threshold. In an ironic similarity to the diagonal cut, perhaps the only people secure in their isolation from automation are mathematicians probing the bounds of what is computable, and how.

But each one of the rest of us has to wonder if, within our lifetimes, our jobs are automatable. I program for a living, and while a good fraction of what I do is intellectually challenging, there is also some that makes me feel like just an operator.

Many non-technical authors think of Kasparov losing to Big Blue as a major milestone in AI, but that was largely due arriving at a point in time that Moore’s Law delivered enough computing beef to “solve” an exponentially complex game like chess. A more meaningful threshold would be when insight can be computed. For example, could a computer propose an algorithm with the simple elegance of Quicksort?

“Running with the machines” is a temporary strategy at best. That is simply the halfway house between humans doing something and it being fully automated. A more accurate phrase would be “run by the machines”, because cheap human labor is crowdsourced for the kinds of problems that are just barely outside a computer’s (current) reach.

I see two strategies for staying ahead of automation:

The first is to be the one doing the automation. In other words, to be a programmer. (Massive disclaimer: of course I would say that, being a programmer.) More bluntly, be the hunter instead of the hunted. The problem is that not everybody is able or willing to do that.

The second strategy is to be a doctor of machines. Large computing systems show organic behavior, and tending to them often requires the same mindset and behaviors as a doctor diagnosing and tending to patients. I like to draw an analogy to cities. A (relatively) small number of people initially construct the infrastructure (pipes, wires, roads), but a much larger number of people maintain them continuously.

We will have interesting lives.

More on fat vs thin clients

Ex-Googler Amit Patel made an insightful comment on my post about fat and thin clients that I totally agree with, and so I’m just going to reproduce it here in full:

Some thoughts:

1 - Net connectivity does not necessarily mean “thin client”. I can use net connectivity for data and still do a lot of processing on the client.

2 - The server/client power ratio doesn’t matter unless I’m actually trying to solve those large problems.

3 - There are some problems that need large machines and there are also some problems that could fit on either side. We’re not trying to figure out whether web search is going to be running on the phone. The real question is where the small things run.

4 - I do use my phone and tablet when I don’t have net connectivity. They are not bricks (maybe this is different in Androidland). Most of the things I do aren’t big problems. Even some previously big problems that only fit on a big computer now fit on my phone (like maps).

5 - Bandwidth and storage keeps getting better. Latency and availability aren’t improving much. Bandwidth and storage makes the “sync all my data among all my devices” model work for a larger and larger subset of my data. My data is not growing as quickly as storage, so I can see all my data fitting on my phone within a decade.

For any given problem, do I ever want to give up low latency and high availability to have it run on the server instead of my client? Generally, not unless it’s a much better experience to compensate for the slowness and unavailability. For most everything I do (text editing, word processing, photo processing, web browsing, games, email, social networking), it’s hard to justify.

Unfortunately most of today’s client apps are based on the old model assuming no networking. You email files around if you want to share. I think we can do much better by using synchronization among multiple clients as a fundamental building block. Data and compute stay local but when you have connectivity you synchronize with other places the data is stored. Google Wave was a stab at this. OneNote too, I think. Git does this for programming. DropBox is built on this model but it handles only simple synchronization at the moment. They have the potential to build infrastructure for apps to synchronize in a more structured way (like Wave), but I don’t know if they’re planning to do this.

Copyright 2008-2013 Vivek Haldar