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Interrupts Considered Harmful

A True Story:
Setting: a development team which is responsible for a production application. This application processes millions of dollars per day in financial transactions, so it has to run.

As the company had just put our a major release, a developer had to work late shift, just in case something happened. The release had been in production for a few weeks, so the worst problems were over.

A few nights ago, it was Joe's turn for night duty. Joe (not his real name) is a good developer who can be counted on to move one, sometimes two tickets from waiting, through in progress, to done every day.

There were no production problems that night, so Joe could work on his development tasks. How many tickets did Joe finish that night?

Joe was between 2 1/2 and 5 times as productive working at night. Why? Because no one interrupted him.

At the Choose Forum on Human-centric Software Development, Prof. Andrew Ko reported his experience studying software developers at Microsoft: On the average a developer works 10 minutes before having to do a task switch. "Actually completing a task was seldom the reason for a task switch," he noted laconically. The most common reasons were interruptions, ranging from phone calls, IM messages, E-Mails, visits from co-workers, etc.

I think daily interruptions are a kind of micro-multitasking. Every task switch (especially when developing) causes you to lose context. When you come back to the task, you have to figure out where you were, and you've probably forgotten some vital information on the way, which you have to recreate.

Could there really be a factor of 3 potential to improve productivity be removing interruptions? What impact do interrupts have on your work? What do you do to keep interruptions under control?


Anonymous said…
You are so spot on with this.

In my company I've started to notice a new trend, which is really rather bizarre when you think of it:

Developers calling in sick, only to be able to finish their work without interruptions! I'm the lead developer of a small but motivated team of developers and people often come to me for some technical advise. A little over year ago a developer of my team called in sick and I was at first a little surprised when I got an IM of him asking for some help with some method. He initially told me he couldn't sleep and started to do some simple work to pass the time. The next week however he committed in batches quite some amounts of quality code that made it clear he did a 'little more' than some simple work.

A while later during a drink he confessed he wasn't sick at all, but *really* needed to get some work done without being interrupted via email, IM, at the desk, etc like every other 5 minutes.

He was only the first and I noticed an increasing amount of such incidents.

The sick records of my team are now slightly higher than average, but the amount of work being done by my team is a bit more than slightly higher than average.
Jason Stillwell said…
I work in the office 4-6 hours a day, which means I show up between 12-2pm. then I work another 4-6 hours at night, either in the empty office or at home (my choice).

Its the only way I can be productive.
Unknown said…
I'm from the UK and a member of a small development team based in Brussels and now have the relative luxury of working from home most of the time and I've seen a definite improvement in my work, both in quantity and quality.

Luckily my boss is happy for me to perform my work when it suits me (as long as stuff gets delivered on time), rather than the 'you must work 9-5' mentality that is still so prevalent and I feel this has made a real difference.
Peter said…
When I was at Microsoft (in the dark ages, long before working at home was really option), I preferred to come in around 10 or 11am for contact with co-workers, then go home around 4pm. Then I would come back around 7pm - things were much quieter, the Dec-20 (gonzo) was much faster, and in general I got much more work done.
Urs Enzler said…
Interrupts and other disturbances were quite often a topic in our retrospectives.

I think that the only real solution is a disciplined way of communication of the whole team and as far as possible all related peers (inside and outside company).

This includes:
- emails are answered twice a day (turn off notification)
- don't answer the phone if working concentrated on something, let them get to the voice mail
- introduce a "flag" that indicates whether you accept that someone can ask you a question at your desk
- before disturbing someone, ask yourself how concentrated he/she seams to work
- maybe define work hours where no cimmunication is allowed
- before disturbing someone, ask yourself if it is necessary (or can wait until next Stand-up Meeting or break)
- if the team takes a break together, this is a great opportunity to "disturbe"

However, it is important that the team communication works nonetheless. Otherwise, Scrum does not work anymore. Therefore, working home alone or late is really not a solution.

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