Code Churn 101: Everything You Need to Know

In software development, it’s good to incorporate customer feedback in new iterations and continually improve the code base.

However, if you find your teams are constantly having high levels of code churn soon after code is merged into the main branch, it can indicate productivity problems or skill level mismatches.

But what exactly is code churn? How can you measure code churn? And how do you know if your code churn is good or bad?

Here’s what you need to know about code churn in software development.

What Is Code Churn?

Code churn is when you replace previously written code with new code. Old code is removed, and potentially replaced with new code to either enhance functionality or improve the code structure (refactoring).

Code churn is necessary to maintain software, solve bugs, release new iterations, make updates, and add new features. Plus, if code churn simplifies older, longer code, there is less room for bugs to occur — saving your team valuable time.

However, code churn — especially at certain times and in high volumes — can indicate a few problems.

Is Code Churn Bad?

You may be wondering: “Why is code churn bad? Aren’t updates a good thing?”

Code churn is not inherently good or bad. Especially in software development, it’s often necessary as you make updates and have new iterations.

However, too much code churn — or code churn that occurs soon after code has been released — can be a red flag. When you spend time rewriting code immediately, it means that there was something wrong the original implementation.

A few instances when code churn could signal a problem include:

• It happens soon after code is written and the person replacing the code is not the same person who initially wrote it.
• Large amounts of code are removed or restructured following a code review (but before code is merged into the main branch), potentially indicating poor planning or expectation setting.
• Churn happens soon after code is put into production (within a week), indicating bugs or other quality problems that weren’t caught during review
• There is almost never any code churn, which may indicate that nobody is using the code in production or improving code after it is released.

However, code churn can be good when:

• A developer self-edits before initial review
• It is associated with refactoring code to improve its quality
• When incorporating customer and management feedback to extend functionality or cut experimental functionality that didn’t pan out.

How to Measure and Reduce Code Churn

Here’s how to measure how much code churn you have, how to tell if it's good or bad, and how to reduce it.

1. Evaluate Who Is Making Changes

One of the best ways to measure code churn is to track who is making the changes.

From time to time, senior developers may catch a place where code written by a less experienced developer can be refactored to run in fewer lines or with less bugs.

However, you want to ensure this doesn’t happen frequently. You also want to ensure that when it does happen, the senior developer walks through the changes with the newer developer and shows them how to do it. Otherwise, this can create unhealthy power dynamics.

This can help your development team in a few ways:

• Helps show if certain developers are having code churn more frequently than others
• Ensures that senior developers help newer developers grow, facilitating learning
• Keeps team dynamics balanced and healthy, maximizing productivity

If you see certain developers’ code frequently churning with changes from a team member, consider if specific projects are too challenging and better assigned to more senior developers. Or, consider if senior developers can provide better guidance to help a newer developer fix their own code.

2. Consider When Code Churn Is Taking Place

A moderate level of code churn is good and indicates that your developers are:

• Incorporating customer feedback
• Finding places where bugs can be smoothed out in iterations
• Improving code quality

However, the timing of code churn is key.

If code churn happens too soon after it code is integrated into the main branch (within a week), this can indicate that developers are not self-editing or the code review process does not uphold quality.

If it never happens, it can mean that feedback isn’t being incorporated from customers.

Code Churn Happens Before an Initial Review

Code churn before an initial review helps teams maximize productivity. Overall, this is a positive (as long as deadlines are still being met).

This indicates that a developer is self-editing. They’re taking time to evaluate how they can replace code to be more effective and run more smoothly.

It also indicates they’re self-aware and being critical of their own work, which helps save your entire development team time and money.

Code Churn Happens After an Initial Review But Before Going Into Production

It’s not as preferable, but if code churn happens after an initial review and before it goes into production, it is better than code churn after deployment to production.

However, if you see frequent code churn after initial reviews, this can indicate problems with self-review, misalignments with a developer’s skillset, or signs that you need to evaluate your overall processes.

• Are certain developers frequently having more code churn than others?
• Are your developers relying on others to debug their code rather than testing it themselves, or is there a greater problem across the development team where quality expectations are not high enough?

Consider:

• If you can help certain developers refine their self-editing
• If certain projects should be reassigned to other team members
• If setting more clear expectations can help developers submit higher-quality code for review

Code Churn Happens Soon After It Goes Into Production

This is a huge red flag. A lot of code churn soon after merging into the main branch indicates insufficient quality control systems and processes that result in ineffective code review. This can happen if reviewers are not thorough enough in their code reviews, or if the quality of the code and testing systems is so poor that even thorough reviews are likely to miss bugs.

Seriously consider review processes across the team, as well as automated test coverage and manual test procedures to ensure that fewer problems are able to escape the code review process.

Code Churn Almost Never Happens

This is another red flag. Just as too much code churn can signal a problem, it can also cause issues if there’s not enough long-term.

You don’t want lots of code churn within the first week of an iteration. However, because churn and refactoring is an essential part of long-term maintenance, you don’t want to abandon old code completely.

• If developers never iterate on features after they go live, this can signal that they are not gathering and implementing feedback (or that no customers are using the software, so there is no feedback to gather). Updates and new features are important to customers, so they will grow frustrated if their wants and needs aren’t met.
• Management may not be giving the necessary guidance to indicate the need for code to be refactored. This can be because of poor management or management that does not understand technology. In the long run, this can lead to increasing development costs that compound over time. This will eventually cripple an organization’s ability to deliver new functionality.

Code churn more than a month after launching to production can be a good indicator that feature extension or refactoring (improving the quality of code without changing its functionality) are being incorporated.

Ensure that developers have proper guidance and feedback so they put effort into improving old code and are keeping systems up-to-date.

3. Take Advantage of Tools to Help You Evaluate Code Churn and Productivity

It can be difficult and time-consuming to rewrite code.

However, it can create even more problems if you’re not aware of how your team is functioning and how their productivity trends over time. One of the biggest aspects of how to reduce code churn is to know when and where it occurs.

But how do you measure code churn, and how do you keep track of how soon it occurs after production? Luckily, there are tools to help you evaluate this and make impactful changes for your team based on data.

minware, for example, tracks code longevity to assess how code ages over time. This helps your team know the code’s true quality.

It also tracks how much code churn occurs prior to merging. By knowing trends that show you the full lifecycle of code, you can track where code churn occurs.

Empowering you with valuable metrics and actionable insights, minware gives your team a clear path for continuous improvement.

When you learn exactly how your team's code functions over time, you can implement changes to ensure code churn (and other processes) occur when and where they should.

The Bottom Line

Code churn is not a bad thing — but it’s not always good, either. You want to keep an eye on whose code is churned and when.

Just as you want to replace code when necessary, you also want to be sure to reevaluate review processes and project assignments if they are causing productivity issues. After all, in software development, productivity is one of your best assets to helping your company and bottom line grow.