Click here to close now.


Apache Authors: Pat Romanski, Jim Scott, Jnan Dash, Craig Lowell, Liz McMillan

Related Topics: Apache

Apache: Blog Post

Apache Hadoop: Technical Debt Decreased by 14% Through Code Refactoring

Initial Technical Debt of the project reduced from 136 to 117 days of remediation

Technical Debt is worth nothing if no pragmatic action is taken into code, in order to control and tackle it. To illustrate Scertify's capability to automatically correct code defects that increase this unintended debt, we performed code refactoring on two subprojects of the Hadoop project : Hadoop Common and Hadoop Mapreduce. Thanks to Scertify, we were able to correct 25K defects in 2 minutes. In other words, 14% of the Technical Debt has been written-off without any human effort needed.

Initial analysis
According to Wikipedia, Apache Hadoop is "an open-source software framework that supports data-intensive distributed applications". This framework contains several projects, Common and Mapreduce are two important ones with respectively 120K and 162K lines of code (blank lines and comments excluded). The version we worked with is the last development version : 3.0.0-SNAPSHOT. We ran Scertify Refactoring Assessment, our open-source plugin for Sonar, on the projects, in order to get an overview of their technical debt. Technical debt is defined as the amount of time needed to correct all defects detected. As you can see on screen-shots below, Common has a technical debt of 70 days and Mapreduce of 66 days. Scertify Refactoring Assessment also computes the potential of automatic correction of the technical debt : the debt write-off. They both have a good potential for automatic refactoring, respectively 38 and 36 days. So, the next step is to use Scertify to perform this automatic refactoring. By the way, if you would like to try it with your own source code, a trial version of Scertify is available here.

Hadoop Common Original Techdebt

Hadoop Mapreduce Original Technical debt

We scrolled among the various errors and we chose 8 rules to perform the demonstration.

Refactoring rules for the demonstration

Here's a presentation of the refactoring rules we used in this demonstration. As you can see, some rules need parameters to be efficient. This is the case of rules regarding logging. The logging framework used in those project is Apache Common logging, so we configured the rules to use this framework.


This rule reports a violation when it finds a code that catch an expression and print its stack trace to the standard error output. A logging framework should be used instead, in order to improve application's maintainability. The refactoring replace a call to print stack trace by a call to a logging framework. The rule can also declare the logger in the class and make the required imports. Here's an example of the original code and the refactored code in the class GenericWritable.

Original code:

catch (Exception e) {
      throw new IOException("Cannot initialize the class: " + clazz);

Refactored code:

catch (final Exception e) {
      LOG.error(e.getMessage(), e);
      throw new IOException("Cannot initialize the class: " + clazz);

In this case, LOG was not declared so it was added to the class and import were made :

private static final Log LOG = LogFactory.getLog(GenericWritable.class);

Calling the constructor of a wrapper type, like Integer, to convert a primitive type is a bad practice. It is less efficient than calling the static method valueOf.


This rule checks that literals are in the first position in comparisons. The refactoring invert the literal and the variable. This ensures that the code cannot crash due to the variable being a null pointer.


Using the concatenation of an empty string to convert a primitive type to a String is a bad practice. First of all, it makes the code less readable. It is also less efficient in most cases (the only case where the string concatenation is slightly better is when the primitive is final). Here's an example taken from class MD5MD5CRC32FileChecksum.

Original code:

xml.attribute("bytesPerCRC", "" + that.bytesPerCRC);

Refactored code:

xml.attribute("bytesPerCRC", String.valueOf(that.bytesPerCRC));

When a concatenation of String is performed inside a debug log, one should check if debug is enabled before making the call. Otherwise, the String concatenation will always be done. The refactoring adds a guard before the call to debug. In this case, it is configured to use the method isDebugEnabled(), since we use Apache's log. Below is an example of refactored code taken from class ActiveStandByElector:

        LOG.debug("StatNode result: " + rc + " for path: " + path + " connectionState: " + zkConnectionState + " for " + this);


This rule finds if statements that don't use braces. The refactoring adds required braces.


This rule finds usage of Collection's size method to check if a collection is empty. Rather than using size(), it is better to use isEmpty() making the code easier to read. The refactoring replace comparisons between size and 0 with a call to isEmpty().


This method flags local variables that could be declared final and are not. The use of the final keyword is a useful information for future code readers. The refactoring adds the "final" keword. This is not a critical rule, but since it has a huge number of violations, it is useful to get rid of them quickly with automatic refactoring.

Scertify's refactoring results
So we ran Scertify on both projects to detect and refactor those rules. On each project it took around 1 minute to perform the full process. Scertify generates an html report with information on errors detected and corrected. Below is a summary of all errors corrected in the two projects. Many minor things were corrected, but also more important ones. Overall, it took 2 minutes to correct 25392 defects. Not so bad isn't it? Those defects include both minor violations and more critical violations in term of maintainability, performance or robustness.

Violations refactored

As you can see on screen-shots below, with those defects corrected the technical debt of each project has been reduced of 10 days. Overall, that's 20 day of technical debt that have been written-off.

Refactored Common technical debt

Refactored Mapreduce technical debt

Last but not least, Hadoop contains many unit tests and of course we made sure that they still succeed after the refactoring. To conclude, thanks to Scertify's refactoring features we were able to efficiently correct 25K defects in few minutes. We are glad to make the refactored code available to community, you can download it below. We will continue to do such refactoring on open-source applications, so if you have an idea for an open-source project that could leverage such refactoring, just let us know!

Download the source files

More Stories By Michael Muller

Michael Muller, a Marketing Manager at Tocea, has 10+ years of experience as a Marketing and Communication Manager. He specializes in technology and innovative companies. He is executive editor at, a French IT magazine and the creator of, a cool URL shortener. Dad of two kids.

@ThingsExpo Stories
Just over a week ago I received a long and loud sustained applause for a presentation I delivered at this year’s Cloud Expo in Santa Clara. I was extremely pleased with the turnout and had some very good conversations with many of the attendees. Over the next few days I had many more meaningful conversations and was not only happy with the results but also learned a few new things. Here is everything I learned in those three days distilled into three short points.
As organizations realize the scope of the Internet of Things, gaining key insights from Big Data, through the use of advanced analytics, becomes crucial. However, IoT also creates the need for petabyte scale storage of data from millions of devices. A new type of Storage is required which seamlessly integrates robust data analytics with massive scale. These storage systems will act as “smart systems” provide in-place analytics that speed discovery and enable businesses to quickly derive meaningful and actionable insights. In his session at @ThingsExpo, Paul Turner, Chief Marketing Officer at...
DevOps is about increasing efficiency, but nothing is more inefficient than building the same application twice. However, this is a routine occurrence with enterprise applications that need both a rich desktop web interface and strong mobile support. With recent technological advances from Isomorphic Software and others, rich desktop and tuned mobile experiences can now be created with a single codebase – without compromising functionality, performance or usability. In his session at DevOps Summit, Charles Kendrick, CTO and Chief Architect at Isomorphic Software, demonstrated examples of com...
In his General Session at 17th Cloud Expo, Bruce Swann, Senior Product Marketing Manager for Adobe Campaign, explored the key ingredients of cross-channel marketing in a digital world. Learn how the Adobe Marketing Cloud can help marketers embrace opportunities for personalized, relevant and real-time customer engagement across offline (direct mail, point of sale, call center) and digital (email, website, SMS, mobile apps, social networks, connected objects).
The Internet of Everything is re-shaping technology trends–moving away from “request/response” architecture to an “always-on” Streaming Web where data is in constant motion and secure, reliable communication is an absolute necessity. As more and more THINGS go online, the challenges that developers will need to address will only increase exponentially. In his session at @ThingsExpo, Todd Greene, Founder & CEO of PubNub, exploreed the current state of IoT connectivity and review key trends and technology requirements that will drive the Internet of Things from hype to reality.
Two weeks ago (November 3-5), I attended the Cloud Expo Silicon Valley as a speaker, where I presented on the security and privacy due diligence requirements for cloud solutions. Cloud security is a topical issue for every CIO, CISO, and technology buyer. Decision-makers are always looking for insights on how to mitigate the security risks of implementing and using cloud solutions. Based on the presentation topics covered at the conference, as well as the general discussions heard between sessions, I wanted to share some of my observations on emerging trends. As cyber security serves as a fou...
Continuous processes around the development and deployment of applications are both impacted by -- and a benefit to -- the Internet of Things trend. To help better understand the relationship between DevOps and a plethora of new end-devices and data please welcome Gary Gruver, consultant, author and a former IT executive who has led many large-scale IT transformation projects, and John Jeremiah, Technology Evangelist at Hewlett Packard Enterprise (HPE), on Twitter at @j_jeremiah. The discussion is moderated by me, Dana Gardner, Principal Analyst at Interarbor Solutions.
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
The Internet of Things is clearly many things: data collection and analytics, wearables, Smart Grids and Smart Cities, the Industrial Internet, and more. Cool platforms like Arduino, Raspberry Pi, Intel's Galileo and Edison, and a diverse world of sensors are making the IoT a great toy box for developers in all these areas. In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists discussed what things are the most important, which will have the most profound effect on the world, and what should we expect to see over the next couple of years.
With all the incredible momentum behind the Internet of Things (IoT) industry, it is easy to forget that not a single CEO wakes up and wonders if “my IoT is broken.” What they wonder is if they are making the right decisions to do all they can to increase revenue, decrease costs, and improve customer experience – effectively the same challenges they have always had in growing their business. The exciting thing about the IoT industry is now these decisions can be better, faster, and smarter. Now all corporate assets – people, objects, and spaces – can share information about themselves and thei...
PubNub has announced the release of BLOCKS, a set of customizable microservices that give developers a simple way to add code and deploy features for realtime apps.PubNub BLOCKS executes business logic directly on the data streaming through PubNub’s network without splitting it off to an intermediary server controlled by the customer. This revolutionary approach streamlines app development, reduces endpoint-to-endpoint latency, and allows apps to better leverage the enormous scalability of PubNub’s Data Stream Network.
I recently attended and was a speaker at the 4th International Internet of @ThingsExpo at the Santa Clara Convention Center. I also had the opportunity to attend this event last year and I wrote a blog from that show talking about how the “Enterprise Impact of IoT” was a key theme of last year’s show. I was curious to see if the same theme would still resonate 365 days later and what, if any, changes I would see in the content presented.
Apps and devices shouldn't stop working when there's limited or no network connectivity. Learn how to bring data stored in a cloud database to the edge of the network (and back again) whenever an Internet connection is available. In his session at 17th Cloud Expo, Ben Perlmutter, a Sales Engineer with IBM Cloudant, demonstrated techniques for replicating cloud databases with devices in order to build offline-first mobile or Internet of Things (IoT) apps that can provide a better, faster user experience, both offline and online. The focus of this talk was on IBM Cloudant, Apache CouchDB, and ...
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem" in this scenario: microservice A (releases daily) depends on a couple of additions to backend B (re...
Discussions of cloud computing have evolved in recent years from a focus on specific types of cloud, to a world of hybrid cloud, and to a world dominated by the APIs that make today's multi-cloud environments and hybrid clouds possible. In this Power Panel at 17th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists addressed the importance of customers being able to use the specific technologies they need, through environments and ecosystems that expose their APIs to make true change and transformation possible.
There are over 120 breakout sessions in all, with Keynotes, General Sessions, and Power Panels adding to three days of incredibly rich presentations and content. Join @ThingsExpo conference chair Roger Strukhoff (@IoT2040), June 7-9, 2016 in New York City, for three days of intense 'Internet of Things' discussion and focus, including Big Data's indespensable role in IoT, Smart Grids and Industrial Internet of Things, Wearables and Consumer IoT, as well as (new) IoT's use in Vertical Markets.
Container technology is shaping the future of DevOps and it’s also changing the way organizations think about application development. With the rise of mobile applications in the enterprise, businesses are abandoning year-long development cycles and embracing technologies that enable rapid development and continuous deployment of apps. In his session at DevOps Summit, Kurt Collins, Developer Evangelist at, examined how Docker has evolved into a highly effective tool for application delivery by allowing increasingly popular Mobile Backend-as-a-Service (mBaaS) platforms to quickly crea...
The Internet of Things (IoT) is growing rapidly by extending current technologies, products and networks. By 2020, Cisco estimates there will be 50 billion connected devices. Gartner has forecast revenues of over $300 billion, just to IoT suppliers. Now is the time to figure out how you’ll make money – not just create innovative products. With hundreds of new products and companies jumping into the IoT fray every month, there’s no shortage of innovation. Despite this, McKinsey/VisionMobile data shows "less than 10 percent of IoT developers are making enough to support a reasonably sized team....
The cloud. Like a comic book superhero, there seems to be no problem it can’t fix or cost it can’t slash. Yet making the transition is not always easy and production environments are still largely on premise. Taking some practical and sensible steps to reduce risk can also help provide a basis for a successful cloud transition. A plethora of surveys from the likes of IDG and Gartner show that more than 70 percent of enterprises have deployed at least one or more cloud application or workload. Yet a closer inspection at the data reveals less than half of these cloud projects involve production...
Internet of @ThingsExpo, taking place June 7-9, 2016 at Javits Center, New York City and Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 18th International @CloudExpo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo New York Call for Papers is now open.