PHP APC and Handling Dynamic Inheritance Opcodes

PHP APC and Handling Dynamic Inheritance Opcodes

Gopal Vijayaraghavan, one of the core APC developers, has a very good write-up (APC Autofilter: The Real Story) on the consequences of static and dynamic inheritance on opcodes generated by the compiler as well as how APC handles them. If you’re familiar with it, you might want to skip right to ‘Handling Dynamic Opcodes’ where we focus on some discrepancies we found as well as how to make things perform better. Continue reading

BarCampBoston is so good it’s spooky!

A group of engineers from Wayfair will pause trying to make Halloween pictures in Graphite and stop looking for a ghost in the machine with Skyline this weekend to head over to the 8th reincarnation of BarCampBoston.

BarCampBoston is a great example of an unconference. These conferences are filled with their own kind of tech conf magic, so if you haven’t registered yet, I’d put down your magic wand and signup quick!. 600+ attendees will be headed to the MIT Stata Center this weekend like a swarm of undead, showing how very much alive the Boston tech scene is.

Over the past 7 years the event has continued to grow in size and popularity without losing the unconference spirit and feel. It will be interesting to see how this year’s event handles keeping with the unconference model at such a scale. Some of the normal process at an unconference is geared more for smaller groups, so I wouldn’t be frightened if things need to be tweaked a little to work for such a large crowd.

We look forward to seeing all of the talks that are conjured up at BarCampBoston this weekend!

Improving German Solr/Lucene search results

On the search and recommendations team at Wayfair, we like to think of ourselves as sophisticated men and women of the world.  We have speakers of French, Chinese, Hebrew, German and Persian in the crew.  Some of us host couchsurfers at our swanky apartments, and then turn around and couchsurf all over Europe.  Others travel to Singapore, attend music festivals in Thailand, etc., etc.  But until recently, when it came to giving our German-speaking customers a decent search experience, we could fairly have been characterized as inhospitable xenophobes. Continue reading

Dynamic WAN Optimizer Routing

Wayfair recently deployed Steelhead WAN optimizers in our network.  We were unsatisfied with the 3 (2.5?) main suggested methods of deployment from Riverbed.  So we designed our own deployment.  But first, the vendor suggested methods: Continue reading

Stormin’ OMS


There’s storm in Wayfair! And yes, the “a” article before the word “storm” is purposely not there. When referring to “storm” at Wayfair, we do not mean a conglomerate of barometric circumstances that lead to downpours from the skies and other natural phenomena (a storm); we mean real-time computation, horizontal scalability, and system robustness. We mean bleeding edge technologies (a storm). Wayfair’s Order Management System (OMS) team introduced storm into our ever-growing technical infrastructure in February to implement event driven processes. Continue reading

/dev/null vs. MongoDB benchmark bake-off

We’ve used MongoDB at Wayfair for a subset of our customer data for a while.  But we’re always looking for opportunities to speed up our infrastructure and give our customers a more responsive user experience.  So when we heard about a new database platform called ‘/dev/null’, we became pretty excited.  We can’t post a link, because it’s in a very private beta testing phase, but we can assure you that the stealth-mode startup that’s working on it is supported by a pair of high-class Silicon Valley VCs.  The technology is supposed to be too cutting-edge for stodgy Boston, so we felt pretty lucky to be included.  /dev/null is web scale, we heard, and it supports sharding!  The slashes in the name certainly give it an edgy feel.  IMHO it’s a bold move to name it that, because of the potential for gfail (weird names doing badly in Google search) and unexpected placement in alphabetical lists.  But hey, as an NYC cabbie character said in Taxi Driver, they’re way ahead of us out there in California.

Everything comes with trade-offs, and the word on the street is that /dev/null is so heavily optimized for write performance that ‘read’ reliability can be less than ideal.  But who knows?  Maybe that’s the balance we want for our write-heaviest workloads.

So we got out our testing tools and went to work on a bake-off.  We wanted to simulate real-world conditions as much as possible, so we wrote some PHP scripts that connected to our sharded development Mongo cluster.  On the /dev/null side, configuration of a cluster was pretty easy, as long as you start from a standard posix-style system.

After function-testing the PHP, we wrote a quick Apache Bench script to bake off the two systems.  The results speak for themselves:

Past the upper 90%, MongoDB is a classic hockey stick.  /dev/null starts fast and stays flat, out to the far horizon.  Love it.  I don’t know that we’re ready to switch right away: I’ll be a little uncomfortable while it’s still in beta, and I’ll have to get to the bottom of those unreliable read operations.  But this is looking *very* promising.

For now, I’m going to follow our internal process for new technologies like this, which is to email around a Wayfair Technical Finding (‘WTF’) to all the senior software engineers and architects, so we can put our heads together, evaluate further, and eventually make a plan to roll this out across all our data centers.

Hat tip gar1t on xtranormal.

Proposal to Control Wheelchairs with Google Glass

When our company’s co-founder encouraged all of our Engineering department to participate in the Google Glass Explorer contest, I thought about project ideas that could help people by using the unique features of this new augmented-reality technology. I remembered a project that some fellow students did during a robotics class that I took in graduate school. It used eye-tracking technology to remotely control the motors on a vehicle. After confirming that Google planned to embed eye-tracking technology in their new product, I realized this idea could work for applications such as wheelchairs.

My plan is to provide feedback about the wearer’s surroundings, including obstacles and suggested paths, and enable him or her to control the wheelchair with eye movements. The original student project used patterns of a user’s eyes being opened or closed to change between types of motion. For my project, I want to use subtle yet deliberate movements of the eye to let the user interact seamlessly with the surrounding environment. I think this technology could be life-changing for persons with disabilities. I hope that being able to work on this project with the support of the Google Glass Explorer program will help make it a reality.

I wrote up my idea, posted it on Google Plus with the #ifihadglass hashtag, and some fellow Wayfairians tweeted about it. Walter Frick of BostInno saw a tweet, did an interview with me, and then wrote an article about it. You can read the full story at these links:

Popular Science write-up:

Tesla: Feel the Power

Data Warehousing at Wayfair

In 2009 Wayfair’s database infrastructure was based almost entirely on Microsoft SQL Server. Our Business Intelligence team was using a SQL Server data warehouse to prepare a large amount of data for import into Analysis Services (SSAS) each day. We populated our data warehouse using transaction log shipping from production servers, which required about 3 hours of downtime on the data warehouse at midnight each night to restore the previous day’s logs. Once that was done, a series of stored procedures were kicked off by jobs that would crunch through data from several different servers to produce a star schema that could be pulled into SSAS. Wayfair was scaling rapidly, and this approach started to become painfully slow, often taking 10-16 hours to crunch through the previous day’s data.

The BI team decided to look into other solutions for data warehousing, and ultimately purchased a Netezza appliance. Netezza is essentially a fork of PostgreSQL that takes a massively parallel cluster of nodes (24 in our case) and makes them look like one database server to the client. In our tests, Netezza could crunch through our data in roughly a quarter of the time, bringing 10-16 hours down to a much more reasonable 2-4 hours. The dream of updating our data warehouse multiple times each day was starting to look feasible. The feedback loop on business decisions would become dramatically shorter, enabling us to iterate more quickly and make well informed decisions at a much faster pace. There was just one glaring problem.

Great, But How Are We Going to Get Data Into It?

As soon as the DBA team heard that the Netezza purchase had been finalized, our first question was “great, but how are we going to get data into it?” The folks at Netezza didn’t have an answer for us, but they did send us an engineer to help devise a solution. As it turned out, the problem of how to incrementally replicate large amounts of data into a data warehouse was a common one, and there were surprisingly few open source solutions. Google it, and most people will tell you that they just reload all their data every day, or that they only have inserts so they can just load the new rows each day. “Great, but what if you want incremental replication throughout the day? What if you have updates or deletes? How do you deal with schema changes?” Crickets.

The First Solution

The solution we arrived upon was to use SQL Server Change Tracking to keep track of which rows had changes on each table, and we built a replication system around that. We created stored procedures for each table that contained the commands required to use the CHANGETABLE() function to generate change sets, dump those to flat files on a network share using bcp, pipe them through dos2unix to fix the line endings, and load them into netezza using the proprietary nzload command. Over the course of a few months we came up with an elaborate series of REPLACE() functions for text fields to escape delimiters, eliminate line breaks and clean up other data anomalies that had the potential to break the nzload. The whole process was driven by SSIS packages.

This solution worked, but it was a maintenance nightmare. We frequently had to edit stored procedures when adding new columns, and we had to edit the SSIS packages to add new tables. SSIS uses GUI based programming, and the editor for it (Business Intelligence Development Studio) is extremely slow and clunky, so even making simple changes was a painful process. Adding a new table into change tracking was a 14-step process that took over an hour of DBA time, and setting up a new database took roughly 28 steps and around two days of DBA time. We also had no solution for schema changes – we needed to manually apply them to the Netezza server, and if we forgot to do so the change tracking jobs would fail.

Release Early, Then Iterate Like Hell

Over the next few years, we iterated on this solution and added a number of useful features. We got rid of the stored procedures per table and switched to a single stored procedure that used dynamic SQL instead. We created a solution for automated schema changes based off of DDL triggers. We created a single stored procedure to handle adding new tables into change tracking, turning it into a one-step process. We added features to publish a subset of a table’s columns, because Netezza had a fixed row size limit that some of our tables exceeded. We added a feature to trim the length of text fields, because large blobs of text usually aren’t needed on the data warehouse and they slowed down the process. We added logging of performance and health metrics to statsD with alerts in Tattle. We added the ability to replicate changes from sharded master databases and consolidate them into one database on the slave. We added the ability to replicate to multiple SQL Server data warehouses in addition to Netezza. We had data on our masters that was moved into archive tables when certain criteria were met, so we added a feature to apply changes to a table and its archive in one transaction on the slave to eliminate the temporary appearance of duplicate data.

Not Good Enough

Ultimately, we were still unhappy with the solution. It was too heavily based on stored procedures, functions, configuration via database tables, xp_cmdshell, and worst of all – linked servers. It was still a nightmare to set up new databases, and when wanted to make changes we had to edit the same stored procedures in 20+ different places.  It was still single threaded. Worst of all, it was tightly coupled. If one slave server fell behind, the others suffered for it. It was also extremely specific to the use case of replicating data from SQL Server to either SQL Server or Netezza, and Wayfair was beginning to make much more use of open source databases like MySQL and MongoDB. In early 2012, we realized this solution wasn’t going to scale any further through iteration. We needed a redesign. We needed something fresh.

Enter Tesla

Redesigned from the ground up and inspired by the Tesla Replicator in The Prestige, Tesla was the solution to our data warehousing woes. We completely avoided stored procedures, functions, configuration tables, SSIS, dynamic SQL, xp_cmdshell and linked servers. Instead, we wrote Tesla in C# (primarily due to one incredibly useful .NET class for copying data between SQL servers) and moved all the logic into the application. Tesla is a single console application that takes care of everything we were doing with stored procedures and SSIS before. Its configuration is based on files rather than tables, which we can version control and deploy using our push tool. It’s multi-threaded and uses a configurable number of threads, allowing us to replicate the most important databases as quickly as possible. It’s completely decoupled, meaning that if one slave falls behind it doesn’t impact the others. It was also designed to be extensible to other data technologies, both as sources and destinations.

Tesla’s Design

Tesla is built into a few agents such as Master and Slave. These agents are run as scheduled tasks in the scheduler of your choice, and they each have their own configuration files. They are completely decoupled and can be run on separate servers and at separate times.

The design for Tesla was inspired by LinkedIn’s article about DataBus. Specifically, the idea of a master server publishing its change sets to a relay server and the slaves polling the relay for those changes was appealing to us. It meant less load on the masters, and it also meant we could store the change sets in such a way that if a slave fell behind it would be able to get consolidated deltas to more efficiently catch up. The biggest difference between Tesla and DataBus is that we focus on batch-based change sets, rather than streaming. Batches are captured on the master as one semi-consistent view of a database at a given point in a time, reducing the chance of orphaned or incomplete data on the data warehouse. It also makes the most sense for a technology like Netezza, which is terrible at small transactions and great at large batches.

Open Source

Tesla is fully open source and available on github. It currently supports SQL Server as a master, slave and relay server, and Netezza as a slave. It was designed with extensibility in mind, so we expect to add more technologies on both sides over time. We already have a slave adapter for Hive in the works. Feel free to hack away, add features, and submit pull requests!

Wayfair @ Beanpot Hackathon

Wayfair was invited to be a sponsor at this year’s Beanpot Hackathon (link:, held last week at the Microsoft NERD center in  Cambridge.  The concept of a hackathon is so closely related to our core values, that we jumped at the opportunity to participate.  Wylie Conlon, along with others from the nuACM (link:, did a great job organizing this event.

For those unfamiliar, a hackathon is a fantastic display of creativity, technical skills, team work, problem solving, and time management, all compressed into a single marathon event. The beanpot hackathon produced 17 demos, impressive considering the event only lasted about 24-hours.

As the event got underway, the dinner area was buzzing with excitement.  Groups of people informally huddled together, some with a white board to their side, drawing sketches and getting feedback, others researching stuff on their laptops, everyone engaged in the discussion bouncing ideas back and forth.  As different teams solidified, they moved to the main conference room to start building their project.  The one theme that was consistent across all groups was passion for technology, and enthusiasm to get something ready for demo.

Most groups worked through the night, taking short naps between bursts of coding.  We had some of our engineers available as mentors, although most groups seemed to be heads down and not looking for outside assistance.  Near the entrance to the conference room, Wayfair setup a duck pond, available for those needing a fun distraction from their project.  There was a fishing pole, and you could pull a duck from the pond to win a prize.  The rubber duck also serves as a good sounding board for ideas, or debugging code when you are stuck. (link:

By the time Saturday evening arrived, I was blown away by some of the projects that teams put together.  Not only were the demos some cool application, or something that solved a problem, but the presentations were well done.  In many cases, the presenters talked about their inspiration, thought process, and where they saw the idea going next.  Questions from the audience were often constructive and suggested improvements.

Looking back on the event, I think one of the reasons we aligned so well with this particular event is because of the similarities to our work environment — Smart people using technology to solve problems quickly and get things done.  I see that demonstrated every day in our engineering department, and it was refreshing to see so many talented students come together for an event like this.  On a related note, we are hiring for summer internships in our software development group.  If you were a participant at the beanpot hackathon, or this type of environment sounds good to you, please get in touch with us (link:

Brad S.

(contributors: Elias Y., Nishan S.)

Why not give Code Deploy Clients access to the repository?

We’ve received a few online, and in person questions like this, so i figured it was probably worth explaining in a little more detail.

On the Deployment server, we have a variety of applications that we deploy. From Windows .Net Services, Python, Classic ASP, CSS/JS and PHP to name a few.

We chose to standardize the interface to the Deployment server to make creating new code deployment clients simpler. Our Deployment server is essentially an on demand package creation and deployment system. Continue reading