Friday, April 5, 2013

Downstream WIP Limits – Another cooking analogy

I made a rather extensive Sunday brunch a while ago for the family, with a couple of new recipes that I prepared the day before– sweet rolls and a spinach and almond pie (think soufflé in a crust). Both turned out great, but in my “retrospective” after spending the day cooking, I realized I had missed something.

Both recipes had many steps, and since the rolls required quite a bit of time in the bread machine, I made the assumption that I could work on them concurrently (start the rolls in the bread machine, start the pie crust, then the filling, etc.). I goofed.

While the time that I needed to prepare both items could be handled by me, I failed to take into account that both items needed to end up in the oven – at very different temperatures.  I handled my WIP (work in progress) limit just fine, but paid no attention to the oven’s WIP limit of ONE. Everything turned out fine, but it meant that I had to delay baking the pie (the rolls took priority, since they HAD to go in the oven once they had risen sufficiently). My afternoon of baking ran well into the evening. Not that I was busy the whole time. I just had to wait on the oven.  

This story illustrates the reasons why lean processes seek  to reduce the 3 M’s – muri (overburden), muda (waste), and mura (unevenness). I experienced mura, because I had to wait on the oven’s availability, then rush to finish the job. The oven was dealing with muri, as it needed to respond to multiple requests and couldn’t. And I experienced muda, as I wasted a beautiful evening waiting on the oven, when I could’ve gone for a bike ride!

This is similar to situations in development, where the 10 developers on a team may not be paying attention to the overload of tasks placed upon the 5 QA engineers; or where the 7 development teams aren’t aware of all the tasks the app support team must do for each team. Unless everyone involved in the process is aware of where the limits (sometimes called bottlenecks) exist, you may find yourself with excess inventory (code waiting to be delivered, or a pie waiting to be baked). The 3 M’s seem to go together - unevenness in the process is a symptom of overburden on one part of the process, and both result in waste, as sections need to wait, and inventory ages.

What can be done to alleviate bottlenecks, or limits? Sometimes, re-allocating staff can help, but only briefly – this isn’t a permanent solution. When you’ve got one thing (like an oven), that just has one task (bake things), the upstream process needs to take that limit into account. When my husband offered to help, there really was nothing he could do, but wait with me. Now, if he could buy me a second oven…

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