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Metrics

Feedback is at the heart of any software delivery process. The best way to improve feedback is to make the feedback cycles short and the results visible. You should measure continually and broadcast the results of the measurements in some hard-to-avoid manner, such as on a very visible poster on the wall, or on a computer display dedicated to showing bold, big results. Such devices are known as information radiators.

The important question, though, is: What should you measure? What you choose to measure will have an enormous influence on the behavior of your team (this is known as the Hawthorne effect). Measure the lines of code, and developers will write many short lines of code. Measure the number of defects fixed, and testers will log bugs that could be fixed by a quick discussion with a developer.

According to the lean philosophy, it is essential to optimize globally, not locally. If you spend a lot of time removing a bottleneck that is not actually the one constraining your delivery process, you will make no difference to the delivery process. So it is important to have a global metric that can be used to determine if the delivery process as a whole has a problem.

For the software delivery process, the most important global metric is cycle time. This is the time between deciding that a feature needs to be implemented and having that feature released to users. As Mary Poppendieck asks, "How long would it take your organization to deploy a change that involves just one single line of code? Do you do this on a repeatable, reliable basis?"4 This metric is hard to measure because it covers many parts of the software delivery process—from analysis, through development, to release. However, it tells you more about your process than any other metric.

Many projects, incorrectly, choose other measures as their primary metrics. Projects concerned with the quality of their software often choose to measure the number of defects. However, this is a secondary measure. If a team using this measure discovers a defect, but it takes six months to release a fix for it, knowing that the defect exists is not very useful. Focusing on the reduction of cycle time encourages the practices that increase quality, such as the use of a comprehensive automated suite of tests that is run as a result of every check-in.

A proper implementation of a deployment pipeline should make it simple to calculate the part of the cycle time corresponding to the part of the value stream from check-in to release. It should also let you see the lead time from the check-in to each stage of your process, so you can discover your bottlenecks.

Once you know the cycle time for your application, you can work out how best to reduce it. You can use the Theory of Constraints to do this by applying the following process.

  1. Identify the limiting constraint on your system. This is the part of your build, test, deploy, and release process that is the bottleneck. To pick an example at random, perhaps it's the manual testing process.
  2. Exploit the constraint. This means ensuring that you should maximize the throughput of that part of the process. In our example (manual testing), you would make sure that there is always a buffer of stories waiting to be manually tested, and ensure that the resources involved in manual testing don't get used for anything else.
  3. Subordinate all other processes to the constraint. This implies that other resources will not work at 100%—for example, if your developers work developing stories at full capacity, the backlog of stories waiting to be tested would keep on growing. Instead, have your developers work just hard enough to keep the backlog constant and spend the rest of their time writing automated tests to catch bugs so that less time needs to be spent testing manually.
  4. Elevate the constraint. If your cycle time is still too long (in other words, steps 2 and 3 haven't helped enough), you need to increase the resources available—hire more testers, or perhaps invest more effort in automated testing.
  5. Rinse and repeat. Find the next constraint on your system and go back to step 1.

While cycle time is the most important metric in software delivery, there are a number of other diagnostics that can warn you of problems. These include

  • Automated test coverage
  • Properties of the codebase such as the amount of duplication, cyclomatic complexity, efferent and afferent coupling, style problems, and so on
  • Number of defects
  • Velocity, the rate at which your team delivers working, tested, ready for use code
  • Number of commits to the version control system per day
  • Number of builds per day
  • Number of build failures per day
  • Duration of build, including automated tests

It is worth considering how these metrics are presented. The reports described above produce a huge amount of data, and interpreting this data is an art. Program managers, for example, might expect to see this data analyzed and aggregated into a single "health" metric that is represented in the form of a traffic light that shows red, amber, or green. A team's technical lead will want much more detail, but even they will not want to wade through pages and pages of reports. Our colleague, Julias Shaw, created a project called Panopticode that runs a series of these reports against Java code and produces rich, dense visualizations (such as Figure 5.8) that let you see at a glance whether there is a problem with your codebase and where it lies. The key is to create visualizations that aggregate the data and present them in such a form that the human brain can use its unparalleled pattern-matching skills most effectively to identify problems with your process or codebase.

Figure 5.8

Figure 5.8 A tree map generated by Panopticode showing cyclomatic complexity for a Java codebase

Each team's continuous integration server should generate these reports and visualizations on each check-in, and store the reports in your artifact repository. You should then collate the results in a database, and track them across every team. These results should be published on an internal website—have a page for each project. Finally, aggregate them together so that they can be monitored across all of the projects in your development program, or even your whole organization.

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