Pair Development

If you’ve worked on large open source projects, one of the difficulties is dividing the workload. The goal, of course, is to spread it out so that every developer has a workload that will keep them busy, and everyone is working in sync towards a common goal. This isn’t easy in practice, as there is no top-down authority to hand out assignments and keep everyone on track, as there is in a corporate development environment. It requires a good deal of communication among the members of the team, as well as a good deal of trust.

This problem was brought to light recently in the Nova community. The issue was with the subteam working on the scheduler/placement engine, of which I’m a member. During the Newton development cycle, there was a significant bottleneck due to the fact that one person, Chris Dent, was responsible for a large chunk of work in designing and coding the Placement API and underlying engine, while the rest of us could only help by doing reviews after the code was written. And this isn’t a new thing: during Mitaka, it was Jay Pipes who was the bottleneck with the development of the Resource Providers concept, and in Liberty, it was Sylvain Bauza with the huge amount of work he did to integrate the Request Spec into Nova. Don’t get me wrong: I’m not criticizing any of these people, as they all did great work. Rather, I am expressing frustration that they bore the brunt of the load, when it didn’t have to be that way. I think that it is time to try a different approach in Ocata.

I propose that we use Pair Development. No, not Pair Programming – that’s an entirely different thing. Pair Development is when each “chunk” of work is not undertaken by a single developer, but rather to two. They discuss the path they want to take ahead of time, and instead of splitting the work, they both work on the same patches at the same time. Wait, you say – won’t this slow things down? I don’t believe that it will, for several reasons. First, when discussing a design, having multiple sets of eyes will reduce the number of dead ends, in the same way that bugs are reduced in pair programming by having both developers review the code as it is being written. Second, when a reviewer finds an issue with a patch, either developer can make the fix. This is an even greater benefit if the two developers are in different, but overlapping, time zones.

We also have as evidence the week before the most recent Feature Freeze: the placement stuff needed to get in before FF, and so a whole group of us pulled together to make that happen. Having a diverse set of eyes uncovered several edge cases and inconsistencies in the code, and those were resolved pretty quickly. We used IRC mostly, but had a Google Hangout at least once a day to discuss any outstanding, unresolved matters, so that we would all be on the same page. So yeah, the time pressure helped instill a bit of urgency in us all, but I think that it was having all of us own the code, not just Chris, that made things happen as well as they did. I know that I was familiar with the code, having reviewed much of it before, but now that I had to change it and test it myself, my understanding grew much deeper. It’s amazing how deeper you understand something when you touch it instead of just look at it.

Another benefit of pair development is that it provides much more continuity when one of the developers takes some time off. Instead of the progress getting put on hold, the other member of the development pair can continue along. It will also help to have more than one person know the new code intimately, so that when a behavior surfaces that is not expected, we aren’t depending on a single person to figure out what’s going on.

So for Ocata, let’s figure out the tasks, and make sure that each has two people assigned to it. I will wager that come the end of the cycle, it will help us accomplish much more than we have in previous releases.

1 thought on “Pair Development”

  1. We’ve done this very successfully when the pairs are in different time zones, but have a small window of overlap. For example with one person in the US, and one in the UK – having 1-3 hours of overlap time where both are online at the same time.

    Essentially both people need to agree on the common objective, need to ensure that there are daily discussions around contentions to remove road blocks and need to trust each other’s work.

    The work method is essentially to ensure that each person properly documents their work as they go (code comments and such), keeps a TODO list of things that may need to be done (in code or in the commit message), and does at least one upload review of work done around the time when their tag team partner comes online. The crossover time is then used to discuss all the changes made, the TODO items, etc.

    When it works, it works really well. 🙂

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