Wednesday, June 11, 2008

Sustainable Pace: Supply vs Demand

In a traditional project, the demand for resources from the four major aspects of software development see-saws dramatically over the course of a project. These aspects are project management and planning, architecture and design, development, and QA. You need resources on hand to serve the peak demand level, but during periods of low demand those resources will either be idle or used for activities which have a lower ROI.

A common circumstance is that there are insufficient resources on hand for the peak demand level and so people end up working in “crunch mode.” During crunch time, people tend to make more mistakes. Agile levels demand out over time and removes this see-saw effect which simplifies resource planning and removes the need for crunch time.

In the figure above, the straight green lines represent the resource load in an Agile project and the zig-zagging purple lines represent the resource load in a traditional project.

With traditional development, delays during development compress most of the testing to the end of the process which then requires taking shortcuts due to schedule pressure. I used to think that one way of compensating for insufficient QA resources was to delay the release until QA finishes. On the surface it seems to make sense. But only if the folks writing code sit on their hands while QA does their work. Ok, so you have multiple projects and the developers work on another project. But then they finish that. Now QA starts on the second project and the developers move to the third. The problem is still there.

On the other hand, as a result of the need for increased QA resources during testing, you may have two other problems. If you have enough QA resources to handle the pressure of the endgame, you may have too many QA resources during the rest of your development cycle. Alternatively, you may bring on additional QA resources on a short-term basis to compensate. Both of these options are obviously undesirable.

There’s a natural balance between the amount of effort required for developing something and the amount of effort required to QA it. No matter what you do, if you have the wrong ratio of development resources to QA resources, it will cause problems. If development creates more than QA can absorb, you will create a backlog of QA work that will always grow.

There are six options for dealing with a QA backlog: do less QA than needed and thus shift the burden of finding problems that you could have found onto your customers, increase your QA capacity, decrease your development capacity, have development idle, have development help with QA or allow the backlog to grow. The larger your testing backlog, the longer it will take to ship it and the greater your opportunity cost.

The imbalance may be in either direction. After you transition to Agile development, you may find that you have more QA resources than are needed. In that case, you have the option of having QA take on some of the work currently done by developers. See The Role of QA in an Agile Project for more on that topic.

This natural balance holds between all four aspects of software development. Depending on your organization, there may be an imbalance between supply and demand at any stage in the pipeline. Wherever there is an imbalance you have the same six options as described above. For example, you may end up with project plans that are never used, developers idle because the design isn’t ready yet, etc. To the extent that some of the resources are actually the same people you can use that fact to manage this problem.

When using short iterations, resource imbalances are easier to detect and correct. Having balanced resources means that all development activities are done consistently and on a regular basis and there is no need to take the shortcuts that are typical of traditional development.

The Usability of Short Iterations

TOC: Zero to Hyper Agile in 90 Days or Less


Ilja Preuß said...

I see another option: reduce specialization. For example, let developers help the QA folks when the need arises.

Damon Poole said...

Hi Ilja,

Thanks for visiting, nice to "see" you again, looking forward to meeting you at Agile 2008.

I agree with you, I previously posted on that specifically in two other posts on The role of QA in Agile Development and skippped it entirely here.

I have now updated this post to include the option you mention and added a pointer to the QA posts.