To the flow with Don Reinertsen: Waiting comes to an end – Queues in Management
And if they haven’t changed anything yet, they’re still waiting…
Who doesn’t know it, we make a quick trip to the supermarket to pick up one or two more ingredients for the dish we want to prepare for our loved ones tonight. The ingredients are quickly grabbed and then we discover the long line at the checkout. The task that could have been done so quickly starts to take time. The reason: the waiting time. At the checkout, we get nervous: “We have an appointment at 8 p.m., don’t we?” Our elaborate and so sacred schedule gets mixed up. Every step was planned and we were at “optimal” capacity, but now this delay interferes.
Unfortunately, we don’t only find queues and delays when we go shopping, our working world in particular is full of them. Here the consequences are not only that our customers or guests have to wait for their “meal”, we miss out on profits during this delay time and perhaps miss an important market window on top of that.
Back at the checkout, things are slow. The cashier is completely busy. We are now presented with two options: A) We postpone our dinner/release and miss valuable time with our friends or at the market. Or B) we hurry to cook, so postpone troubleshooting until the product is on the market, with the risk of scaring away our guests or customers with a lower quality product.
To summarize in plain language, delays cost companies money. They lead to
- increased risk due to changing market and customer situations
- delayed feedback and thus increased costs for unnecessary developments and reduced quality
- increased process costs
- and decreasing motivation among development teams.
So how do we prevent delays? Delays are caused by waiting times. What waiting times might we think now? We fill waiting times immediately with new activities. We have no time to waste. This is the crux of the matter: we look at the individual worker or the individual team and their workload. What we overlook is the work that gets passed from one team or service to another. Queues form in front of these utilized services, delaying the completion of the overall task. Our shopping illustrates this: if our cashier’s service can’t keep up with the checkout, a queue forms. If we had to wait in line first at the sausage counter, then at the bread counter, and then again at the checkout counter, we probably wouldn’t be able to give our dinner until next week.
So we need to manage our queues within the system, the main cause of delays. To do this, it is necessary to understand that queue lengths increase massively with utilization. The intuitive assumption that high utilization leads to faster processing is wrong. The opposite is true. What’s more, queues are formed faster than they are reduced. A traffic jam on the highway forms almost immediately. However, it takes time to dissolve it. Our goal is therefore to optimize the utilization of services and minimize the turnaround time of tasks. This happens in the supermarket when additional checkouts are opened or a fast checkout, for smaller purchases, is offered. If we put short orders in front of long orders, the queue is reduced because short orders block the service for less time.
Another way to reduce waiting times is to use small batch sizes. This refers to the number of related work units, e.g. the tasks in a sprint. These smaller work packages ensure that the work arrives at the service more evenly distributed and that there are no sudden workloads and thus delays. Batch sizes and queue lengths can be limited using Work In Progress (WIP) limits. The WIP is the number of work units that are not yet completed. This can be used to prevent excessive workload and thus the likelihood of queues by refusing to accept further jobs when the WIP limit is reached.
First and foremost, the company is already helped by becoming aware of all the hidden queues. Once these queues become visible, they become tangible and changeable. But as always: Nothing is good until it is done. So take action, because: If you haven’t changed anything yet, you’re probably still waiting.