- Machine Learning Done Wrong — [M]ost practitioners pick the modeling algorithm they are most familiar with rather than pick the one which best suits the data. In this post, I would like to share some common mistakes (the don’t-s).
- Bandits for Recommendations — A common problem for internet-based companies is: which piece of content should we display? Google has this problem (which ad to show), Facebook has this problem (which friend’s post to show), and RichRelevance has this problem (which product recommendation to show). Many of the promising solutions come from the study of the multi-armed bandit problem.
- Droplets — the Droplet is almost spherical, can self-right after being poured out of a bucket, and has the hardware capabilities to organize into complex shapes with its neighbors due to accurate range and bearing. Droplets are available open-source and use cheap vibration motors and a 3D printed shell. (via Robohub)
- Apple’s App Store Approval Guidelines — some of the plainest English I’ve seen, especially the Introduction. I can only aspire to that clarity. If your App looks like it was cobbled together in a few days, or you’re trying to get your first practice App into the store to impress your friends, please brace yourself for rejection. We have lots of serious developers who don’t want their quality Apps to be surrounded by amateur hour.
ENTRIES TAGGED "nosql"
How NoSQL databases scale vertically and horizontally, and what you should consider when building a DB cluster.
Editor’s note: this post is a follow-up to a recent webcast, “Getting the Most Out of Your NoSQL DB,” by the post author, Alex Bordei.
As product manager for Bigstep’s Full Metal Cloud, I work with a lot of amazing technologies. Most of my work actually involves pushing applications to their limits. My mission is simple: make sure we get the highest performance possible out of each setup we test, then use that knowledge to constantly improve our services.
Here are some of the things I’ve learned along the way about how NoSQL databases scale vertically and horizontally, and what things you should consider when building a DB cluster. Some of these findings can be applied to RDBMS as well, so read on even if you’re still a devoted SQL fan. You might just get up to 60% more performance out of that database soon enough. Read more…
High-performing memory throws many traditional decisions overboard
Over the past decade, SSD drives (popularly known as Flash) have radically changed computing at both the consumer level — where USB sticks have effectively replaced CDs for transporting files — and the server level, where it offers a price/performance ratio radically different from both RAM and disk drives. But databases have just started to catch up during the past few years. Most still depend on internal data structures and storage management fine-tuned for spinning disks.
Citing price and performance, one author advised a wide range of database vendors to move to Flash. Certainly, a database administrator can speed up old databases just by swapping out disk drives and inserting Flash, but doing so captures just a sliver of the potential performance improvement promised by Flash. For this article, I asked several database experts — including representatives of Aerospike, Cassandra, FoundationDB, RethinkDB, and Tokutek — how Flash changes the design of storage engines for databases. The various ways these companies have responded to its promise in their database designs are instructive to readers designing applications and looking for the best storage solutions.
Insecure Hardware, Doc Database, Kids Programming, and Ad-Blocking AP
- Researchers Can Slip an Undetectable Trojan into Intel’s Ivy Bridge CPUs (Ars Technica) — The exploit works by severely reducing the amount of entropy the RNG normally uses, from 128 bits to 32 bits. The hack is similar to stacking a deck of cards during a game of Bridge. Keys generated with an altered chip would be so predictable an adversary could guess them with little time or effort required. The severely weakened RNG isn’t detected by any of the “Built-In Self-Tests” required for the P800-90 and FIPS 140-2 compliance certifications mandated by the National Institute of Standards and Technology.
- rethinkdb — open-source distributed JSON document database with a pleasant and powerful query language.
- Teach Kids Programming — a collection of resources. I start on Scratch much sooner, and 12+ definitely need the Arduino, but generally I agree with the things I recognise, and have a few to research …
- Raspberry Pi as Ad-Blocking Access Point (AdaFruit) — functionality sadly lacking from my off-the-shelf AP.
No Managers, Bezos Pearls, Visualising History, and Scalable Key-Value Store
- No Managers — If we could find a way to replace the function of the managers and focus everyone on actually producing for our Students (customers) then it would actually be possible to be a #NoManager company. In my future posts I’ll explain how we’re doing this at Treehouse.
- The 20 Smartest Things Jeff Bezos Has Ever Said (Motley Fool) — I feel like the 219th smartest thing Jeff Bezos has ever said is still smarter than the smartest thing most business commentators will ever say. (He says, self-referentially) “Invention requires a long-term willingness to be misunderstood.”
- Putting Time in Perspective — nifty representations of relative timescales and history. (via BoingBoing)
- Sophia — BSD-licensed small C library implementing an embeddable key-value database “for a high-load environment”.
Constant KV Store, Google Me, Learned Bias, and DRM-Stripping Lego Robot
- Sparkey — Spotify’s open-sourced simple constant key/value storage library, for read-heavy systems with infrequent large bulk inserts.
- The Truth of Fact, The Truth of Feeling (Ted Chiang) — story about what happens when lifelogs become searchable. Now with Remem, finding the exact moment has become easy, and lifelogs that previously lay all but ignored are now being scrutinized as if they were crime scenes, thickly strewn with evidence for use in domestic squabbles. (via BoingBoing)
- Algorithms Magnifying Misbehaviour (The Guardian) — when the training set embodies biases, the machine will exhibit biases too.
- Lego Robot That Strips DRM Off Ebooks (BoingBoing) — so. damn. cool. If it had been controlled by a C64, Cory would have hit every one of my geek erogenous zones with this find.
Retreading old topics can be a powerful source of epiphany, sometimes more so than simple extra-box thinking. I was a computer science student, of course I knew statistics. But my recent years as a NoSQL (or better stated: distributed systems) junkie have irreparably colored my worldview, filtering every metaphor with a tinge of information management.
Lounging on a half-world plane ride has its benefits, namely, the opportunity to read. Most of my Delta flight from Tel Aviv back home to Portland lacked both wifi and (in my case) a workable laptop power source. So instead, I devoured Nate Silver’s book, The Signal and the Noise. When Nate reintroduced me to the concept of statistical overfit, and relatedly underfit, I could not help but consider these cases in light of the modern problem of distributed data management, namely, operators (you may call these operators DBAs, but please, not to their faces).
When collecting information, be it for a psychological profile of chimp mating rituals, or plotting datapoints in search of the Higgs Boson, the ultimate goal is to find some sort of usable signal, some trend in the data. Not every point is useful, and in fact, any individual could be downright abnormal. This is why we need several points to spot a trend. The world rarely gives us anything clearer than a jumble of anecdotes. But plotted together, occasionally a pattern emerges. This pattern, if repeatable and useful for prediction, becomes a working theory. This is science, and is generally considered a good method for making decisions.
On the other hand, when lacking experience, we tend to over value the experience of others when we assume they have more. This works in straightforward cases, like learning to cook a burger (watch someone make one, copy their process). This isn’t so useful as similarities diverge. Watching someone make a cake won’t tell you much about the process of crafting a burger. Folks like to call this cargo cult behavior.
How Fit are You, Bro?
You need to extract useful information from experience (which I’ll use the math-y sounding word datapoints). Having a collection of datapoints to choose from is useful, but that’s only one part of the process of decision-making. I’m not speaking of a necessarily formal process here, but in the case of database operators, merely a collection of experience. Reality tends to be fairly biased toward facts (despite the desire of many people for this to not be the case). Given enough experience, especially if that experience is factual, we tend to make better and better decisions more inline with reality. That’s pretty much the essence of prediction. Our mushy human brains are more-or-less good at that, at least, better than other animals. It’s why we have computers and Everybody Loves Raymond, and my cat pees in a box.
Imagine you have a sufficient amount of relevant datapoints that you can plot on a chart. Assuming the axes have any relation to each other, and the data is sound, a trend may emerge, such as a line, or some other bounding shape. A signal is relevant data that corresponds to the rules we discover by best fit. Noise is everything else. It’s somewhat circular sounding logic, and it’s really hard to know what is really a signal. This is why science is hard, and so is choosing a proper database. We’re always checking our assumptions, and one solid counter signal can really be disastrous for a model. We may have been wrong all along, missing only enough data. As Einstein famously said in response to the book 100 Authors Against Einstein: “If I were wrong, then one would have been enough!”
Database operators (and programmers forced to play this role) must make predictions all the time, against a seemingly endless series of questions. How much data can I handle? What kind of latency can I expect? How many servers will I need, and how much work to manage them?
So, like all decision making processes, we refer to experience. The problem is, as our industry demands increasing scale, very few people actually have much experience managing giant scale systems. We tend to draw our assumptions from our limited, or biased smaller scale experience, and extrapolate outward. The theories we then tend to concoct are not the optimal fit that we desire, but instead tend to be overfit.
Overfit is when we have a limited amount of data, and overstate its general implications. If we imagine a plot of likely failure scenarios against a limited number of servers, we may be tempted to believe our biggest odds of failure are insufficient RAM, or disk failure. After all, my network has never given me problems, but I sure have lost a hard drive or two. We take these assumptions, which are only somewhat relevant to the realities of scalable systems and divine some rules for ourselves that entirely miss the point.
In a real distributed system, network issues tend to consume most of our interest. Single-server consistency is a solved problem, and most (worthwhile) distributed databases have some sense of built in redundancy (usually replication, the root of all distributed evil).
Collaborative filtering with Neo4j
By this time, chances are very likely that you’ve heard of NoSQL, and of graph databases like Neo4j.
NoSQL databases address important challenges that we face today, in terms of data size and data complexity. They offer a valuable solution by providing particular data models to address these dimensions.
On one side of the spectrum, these databases resolve issues for scaling out and high data values using compounded aggregate values, on the other side is a relationship based data model that allows us to model real world information containing high fidelity and complexity.
Neo4j, like many other graph databases, builds upon the property graph model; labeled nodes (for informational entities) are connected via directed, typed relationships. Both nodes and relationships hold arbitrary properties (key-value pairs). There is no rigid schema, but with node-labels and relationship-types we can have as much meta-information as we like. When importing data into a graph database, the relationships are treated with as much value as the database records themselves. This allows the engine to navigate your connections between nodes in constant time. That compares favorably to the exponential slowdown of many-JOIN SQL-queries in a relational database.
How can you use a graph database?
Graph databases are well suited to model rich domains. Both object models and ER-diagrams are already graphs and provide a hint at the whiteboard-friendliness of the data model and the low-friction mapping of objects into graphs.
Instead of de-normalizing for performance, you would normalize interesting attributes into their own nodes, making it much easier to move, filter and aggregate along these lines. Content and asset management, job-finding, recommendations based on weighted relationships to relevant attribute-nodes are some use cases that fit this model very well.
Many people use graph databases because of their high performance online query capabilities. They process large amounts or high volumes of raw data with Map/Reduce in Hadoop or Event-Processing (like Storm, Esper, etc.) and project the computation results into a graph. We’ve seen examples of this from many domains from financial (fraud detection in money flow graphs), biotech (protein analysis on genome sequencing data) to telco (mobile network optimizations on signal-strength-measurements).
Graph databases shine when you can express your queries as a local search using a few starting points (e.g., people, products, places, orders). From there, you can follow relevant relationships to accumulate interesting information, or project visited nodes and relationships into a suitable result.
OSCON 2013 Speaker Series
Our world is filled with unstructured data. By some estimates, it’s as high as 80% of all data.
Unstructured data is data that isn’t in a specific format. It isn’t separated by a delimiter that you could split on and get all of the individual pieces of data. Most often, this data comes directly from humans. Human generated data isn’t the best kind to place in a relational database and run queries on. You’d need to run some algorithms on unstructured data to gain any insight.
Advanced NFL Stats was kind enough to open up their play-by-play data for NFL games from 2002 to 2012. This dataset consisted of both structured and unstructured data. Here is a sample line showing a single play in the dataset:
20121119_CHI@SF,3,17,48,SF,CHI,3,2,76,20,0,(2:48) C.Kaepernick pass short right to M.Crabtree to SF 25 for 1 yard (C.Tillman). Caught at SF 25. 0-yds YAC,0,3,0,27,7 ,2012
This line is comma separated and has various queryable elements. For example, we could query on the teams playing and the scores. We couldn’t query on the unstructured portion, specifically:
(2:48) C.Kaepernick pass short right to M.Crabtree to SF 25 for 1 yard (C.Tillman). Caught at SF 25. 0-yds YAC
There are many more insights that can be gleaned from this portion. For example, we can see that San Francisco’s quarterback, Colin Kaepernick, passed the ball to the wide receiver, Michael Crabtree. He was tackled by Charles Tillman. Michael Crabtree caught the ball at the 25 yard line, gained 1 yard. After catching the ball, he didn’t make any forward progress or yards after catch (“
Writing a synopsis like that is easy for me as a human. I’ve spent my life working with language and trying to comprehend the meaning. It’s not as easy for a computer. We have to use various methods to extract the information from unstructured data like this. These can vary dramatically in complexity; some use simple string lookups or contains and others use natural language processing.
Parsing would be easy if all of the plays looked like the one above, but they don’t. Each play has a little bit different formatting and varies in the amount of data. The general format is different for each type of play: run, pass, punt, etc. Each type of play needs to be treated a little differently. Also, each person writing the play description will be a little different from the others.
As I showed in the synopsis of the play, one can get some interesting insight out of the structured and unstructured data. However, we’re still limited in what we can do and the kinds of queries we can write.
I had a conversation with a Canadian about American Football and the effects of the weather. I was talking about how the NFL now favors domed locations to take weather out as a variable for the Superbowl or NFL championship. With the play-by-play dataset, I couldn’t write a query to tell me the effects of weather one way or another. The data simply doesn’t exist in the dataset.
The physical location and date of the game is captured in the play-by-play. We can see that in the first portion “
20121119_CHI@SF“. Here, Chicago is playing at San Francisco on 2012-11-19. There are other datasets that could enable us to augment our play-by-play. These datasets would give us the physical location of the stadium where the game was played (the team’s name doesn’t mean that their stadium is in that city). The dataset for stadiums is a relatively small one. This dataset also shows if the stadium is domed and the ambient temperature is a non-issue.