Theory of constraints, using a Kanban board to exploit bottlenecks

The theory of constraints comes from the idea that there is at least one constraint in the throughput. This is normally referred to as a bottleneck that slows the production.

Imagine a system that has a continuous throughput and no bottlenecks, this system would be instant e.g. the moment you click to purchase a house, you have moved into it instantly, or a new software feature that you like would to be in production instantly or installed on your desktop.

Constraints slow down the whole or a part of the system. Any improvements you do will help the flow to become better. If the constraint isn’t improving and focus is on another part of the system, one should ask himself, “are you really improving”?

A very general consensus is that if you have a constraint (bottleneck) you should have more people, more machines, more training, better tools and technologies and this could become quite expensive as a result, the question here is where is your focus? On the bottleneck specifically or on the whole system. To resolve a bottleneck is the helicopter view necessary?

According to the theory of constraint there is a simpler method, which can be exploited quite easily within a Kanban system, why don’t we just exploit the bottleneck. Firstly, use the bottleneck to its maximum capacity e.g. are the people working on the bottleneck? Are the people working around the bottleneck itself? Is there any other help available? Can we find any idle time in the bottleneck or any time where the people can do bottleneck work which can reduce the output of the system.

Using a Kanban board to discover bottlenecks

One of the many advantages I have discovered of using Kanban boards, is that bottlenecks quite often reveal themselves, by having work piling up in front of them and other steps being starved of work to do.

In the above example the developers are blocked from pulling work from the TO DO column, because they are at full capacity of 5 WIP. All 5 items are waiting to be moved over into the testing column. 

The testing column is also at its maximum WIP limit of three, and we have two tickets that are stuck with three items being deployed.

The above board is showing a clear indicating problem which is happening. There is nothing happening in the Done - In Progress column, and this may have been built up over a few days. The Kanban board gives a great opportunity to react and start doing something about the bottleneck before it becomes a real problem.

Exploiting a bottleneck

The above is a very simple example where the testing has become a bottleneck, but in reality a bottleneck can be anywhere on the Kanban board. Below are a few examples;

-       making sure the team have got work to do or they could help someone who is stuck

-       building quality to minimise the workload

-       measuring cycle times per stage

-       limit interruptions

-       remove any impediments that could hinder the work

-       Carefully priortise the bottlenecks

-       Try to divide work items into smaller chunks

-       Have different teams work closely with each other

Can a constraint be positive?

People often think that constraints are negative, but in fact, just like in risk management, a positive can come out of a negative. Using the above Kanban board example, imagine at this particular moment in time we get feedback from the stakeholders that they do not need a number of items which are stuck in testing, the question now is can these be moved across into a discarded queue? So now the Kanban board could look like this;

In the above example we can clearly see two tickets have now been discarded due to customer feedback and we can move two tickets from the Doing – Done column over to testing. This is a very simple example, but in reality things can be very different.

Quite often constraints do come from people themselves; for instance, a developer has more knowledge than anyone else in hiss team. All the remaining members quite often keep going to them and asking for help or advice. This in itself is a constraint and can lead to a further topic.

Do constraints work?

Constraints can have a positive effect and a negative effect, on one hand using visual boards (like above) you will be able to see bottlenecks, and this can help in simplifying future decisions. The negative impact of constraints is normally the way people look at them.

Constraints can help simplify thousands of future decisions; this can be;

Deadlines and disciplines.

Using Kanban we can use the cycle time calculation to measure the amount of time a ticket is taking place and the age of the ticket.

Discipline, this is where your top priorities are taken care of, and you can continuously replenish the backlog. With discipline you will have more free time.

Summary

The theory of constraint is a management of bottlenecks. A bottleneck is a process which slows your throughput. Using visualisation can help identify bottlenecks. Identify where the bottleneck is and exploit the constraint. Constraints do not necessarily need to be negative, A team leader, senior developer agile coach themselves can be a constraint.

Reference

1.     The Goal by Eliyahu M Goldratt

2.     The Phoenix Project: by Gene Kim, Kevin Behr, George Spafford

3.     The Disciplined Pursuit of Less, Greg McKeown