Welcome!

Java IoT Authors: Xenia von Wedel, Elizabeth White, Yeshim Deniz, Carmen Gonzalez, Liz McMillan

Related Topics: Java IoT, Industrial IoT, Microservices Expo, IoT User Interface, Apache, @BigDataExpo

Java IoT: Article

Fix Memory Leaks in Java Production Applications

A memory diagnostics approach for production identifies and fixes the root cause of the problem

Adding more memory to your JVMs (Java Virtual Machines) might be a temporary solution to fixing memory leaks in Java applications, but it for sure won't fix the root cause of the issue. Instead of crashing once per day it may just crash every other day. "Preventive" restarts are also just another desperate measure to minimize downtime, but, let's be frank: this is not how production issues should be solved.

One of our customers - a large online retail store - ran into such an issue. They run one of their online gift card self-service interfaces on two JVMs. During peak holiday seasons when users are activating their gift cards or checking the balance, crashes due to OOM (Out Of Memory) were more frequent, which caused bad user experience. The first "measure" they took was to double the JVM Heap Size. This didn't solve the problem as JVMs were still crashing, so they followed the memory diagnostics approach for production as explained in Java Memory Leaks to identify and fix the root cause of the problem.

Before we walk through the individual steps, let's look at the memory graph that shows the problems they had in December during the peak of the holiday season. The problem persisted even after increasing the memory. They could fix the problem after identifying the real root cause and applying specific configuration changes to a third-party software component.

After identifying the actual root cause and applying necessary configuration changes did the memory leak issue go away? Increasing Memory was not even a temporary solution that worked.

Step 1: Identify a Java Memory Leak
The first step is to monitor the JVM/CLR Memory Metrics such as Heap Space. This will tell us whether there is a potential memory leak. In this case we see memory usage constantly growing, resulting in an eventual runtime crash when the memory limit is reached.

Java Heap Size of both JVMs showed significant growth starting Dec 2nd and Dec 4th resulting in a crash on Dec 6th for both JVMs when the 512MB Max Heap Size was exceeded.

Step 2: Identify problematic Java Objects
The out-of-memory exception automatically triggers a full memory dump that allows for an analysis of which objects consumed the heap and are most likely to be the root cause of the out-of-memory crash. Looking at the objects that consumed most of the heap below indicates that they are related to a third-party logging API used by the application.

Sorting by GC (Garbage Collection) Size and focusing on custom classes (instead of system classes) shows that 80% of the heap is consumed by classes of a third-party logging framework

A closer look at an instance of the VPReportEntry4 shows that it contains five strings - with one consuming 23KB (as compared to several bytes of other string objects).This also explains the high GC Size of the String class in the overall Heap Dump.

Individual very large String objects as part of the ReportEntry object

Following the referrer chain further up reveals the complete picture. The EventQueue keeps LogEvents in an Array, which keeps VPReportEntrys in an Array. All of these objects seem to be kept in memory as the objects are being added to these arrays but never removed and therefore not garbage collected:

Following the referrer tree reveals that global EventQueue objects hold on to the LogEvent and VPReportEntry objects in array lists which are never removed from these arrays

Step 3: Who allocates these objects?
Analyzing object allocation allows us to figure out which part of the code is creating these objects and adding them to the queue. Creating what is called a "Selective Memory Dump" when the application reached 75% Heap Utilization showed the customer that the ReportWriter.report method allocated these entries and that they have been "living" on the heap for quite a while.

It is the report method that allocates the VPReportEntry objects that stay on the heap for quite a while

Step 4: Why are these objects not removed from the Heap?
The premise of the third-party logging framework is that log entries will be created by the application and written in batches at certain times by sending these log entries to a remote logging service using JMS. The memory behavior indicates that even though these log entries might be sent to the service, these objects are not always removed from the EventQueue leading to the out-of-memory exception.

Further analysis revealed that the background batch writer thread calls a logBatch method, which loops through the event queue (calling EventQueue.next) to send current log events in the queue. The question is whether as many messages were taken out of the queue (using next) vs put into the queue (using add) and whether the batch job is really called frequently enough to keep up with the incoming event entries. The following chart shows the method executions of add, as well as the call to logBatch highlighting that logBatch is actually not called frequently enough and therefore not calling next to remove messages from the queue:

The highlighted area shows that messages are put into the queue but not taken out because the background batch job is not executed. Once this leads to an OOM and the system restarts it goes back to normal operation but older log messages will be lost.

Step 5: Fixing the Java Memory Leak problem
After providing this information to the third-party provider and discussing with them the number of log entries and their system environment the conclusion was that our customer used a special logging mode that was not supposed to be used in high-load production environments. It's like running with DEBUG log level in a high load or production environment. This overwhelmed the remote logging service and this is why the batch logging thread was stopped and log events remained in the EventQueue until the out of memory occurred.

After making the recommended changes the system could again run with the previous heap memory size without experiencing any out-of-memory exceptions.

The Memory Leak issue has been solved and the application now runs even with the initial 512MB Heap Space without any problem.

They still use the same dashboards they have built to troubleshoot this issue, and to monitor for any future excessive logging problems.

These dashboards allow them to verify that the logging framework can keep up with log messages after they applied the changes.

Conclusion
Adding additional memory to crashing JVMs is most often not a temporary fix. If you have a real Java memory leak it will just take longer until the Java runtime crashes. It will even incur more overhead due to garbage collection when using larger heaps. The real answer to this is to use the simple approach explained here. Look at the memory metrics to identify whether you have a leak or not. Then identify which objects are causing the issue and why they are not collected by the GC. Working with engineers or third-party providers (as in this case) will help you find a permanent solution that allows you to run the system without impacting end users and without additional resource requirements.

Next Steps
If you want to learn more about Java Memory Management or general Application Performance Best Practices check out our free online Java Enterprise Performance Book. Existing customers of our APM Solution may also want to check out additional best practices on our APM Community.

More Stories By Andreas Grabner

Andreas Grabner has been helping companies improve their application performance for 15+ years. He is a regular contributor within Web Performance and DevOps communities and a prolific speaker at user groups and conferences around the world. Reach him at @grabnerandi

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life sett...
An IoT product’s log files speak volumes about what’s happening with your products in the field, pinpointing current and potential issues, and enabling you to predict failures and save millions of dollars in inventory. But until recently, no one knew how to listen. In his session at @ThingsExpo, Dan Gettens, Chief Research Officer at OnProcess, discussed recent research by Massachusetts Institute of Technology and OnProcess Technology, where MIT created a new, breakthrough analytics model for ...
Successful digital transformation requires new organizational competencies and capabilities. Research tells us that the biggest impediment to successful transformation is human; consequently, the biggest enabler is a properly skilled and empowered workforce. In the digital age, new individual and collective competencies are required. In his session at 19th Cloud Expo, Bob Newhouse, CEO and founder of Agilitiv, drew together recent research and lessons learned from emerging and established compa...
20th Cloud Expo, taking place June 6-8, 2017, at the Javits Center in New York City, NY, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy.
Whether your IoT service is connecting cars, homes, appliances, wearable, cameras or other devices, one question hangs in the balance – how do you actually make money from this service? The ability to turn your IoT service into profit requires the ability to create a monetization strategy that is flexible, scalable and working for you in real-time. It must be a transparent, smoothly implemented strategy that all stakeholders – from customers to the board – will be able to understand and comprehe...
DevOps is being widely accepted (if not fully adopted) as essential in enterprise IT. But as Enterprise DevOps gains maturity, expands scope, and increases velocity, the need for data-driven decisions across teams becomes more acute. DevOps teams in any modern business must wrangle the ‘digital exhaust’ from the delivery toolchain, "pervasive" and "cognitive" computing, APIs and services, mobile devices and applications, the Internet of Things, and now even blockchain. In this power panel at @...
Extracting business value from Internet of Things (IoT) data doesn’t happen overnight. There are several requirements that must be satisfied, including IoT device enablement, data analysis, real-time detection of complex events and automated orchestration of actions. Unfortunately, too many companies fall short in achieving their business goals by implementing incomplete solutions or not focusing on tangible use cases. In his general session at @ThingsExpo, Dave McCarthy, Director of Products...
SYS-CON Events has announced today that Roger Strukhoff has been named conference chair of Cloud Expo and @ThingsExpo 2017 New York. The 20th Cloud Expo and 7th @ThingsExpo will take place on June 6-8, 2017, at the Javits Center in New York City, NY. "The Internet of Things brings trillions of dollars of opportunity to developers and enterprise IT, no matter how you measure it," stated Roger Strukhoff. "More importantly, it leverages the power of devices and the Internet to enable us all to im...
Businesses and business units of all sizes can benefit from cloud computing, but many don't want the cost, performance and security concerns of public cloud nor the complexity of building their own private clouds. Today, some cloud vendors are using artificial intelligence (AI) to simplify cloud deployment and management. In his session at 20th Cloud Expo, Ajay Gulati, Co-founder and CEO of ZeroStack, will discuss how AI can simplify cloud operations. He will cover the following topics: why clou...
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo 2016 in New York. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place June 6-8, 2017, at the Javits Center in New York City, New York, is co-located with 20th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry p...
Internet-of-Things discussions can end up either going down the consumer gadget rabbit hole or focused on the sort of data logging that industrial manufacturers have been doing forever. However, in fact, companies today are already using IoT data both to optimize their operational technology and to improve the experience of customer interactions in novel ways. In his session at @ThingsExpo, Gordon Haff, Red Hat Technology Evangelist, will share examples from a wide range of industries – includin...
"We build IoT infrastructure products - when you have to integrate different devices, different systems and cloud you have to build an application to do that but we eliminate the need to build an application. Our products can integrate any device, any system, any cloud regardless of protocol," explained Peter Jung, Chief Product Officer at Pulzze Systems, in this SYS-CON.tv interview at @ThingsExpo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
Internet of @ThingsExpo has announced today that Chris Matthieu has been named tech chair of Internet of @ThingsExpo 2017 New York The 7th Internet of @ThingsExpo will take place on June 6-8, 2017, at the Javits Center in New York City, New York. Chris Matthieu is the co-founder and CTO of Octoblu, a revolutionary real-time IoT platform recently acquired by Citrix. Octoblu connects things, systems, people and clouds to a global mesh network allowing users to automate and control design flo...
Unless your company can spend a lot of money on new technology, re-engineering your environment and hiring a comprehensive cybersecurity team, you will most likely move to the cloud or seek external service partnerships. In his session at 18th Cloud Expo, Darren Guccione, CEO of Keeper Security, revealed what you need to know when it comes to encryption in the cloud.
With 15% of enterprises adopting a hybrid IT strategy, you need to set a plan to integrate hybrid cloud throughout your infrastructure. In his session at 18th Cloud Expo, Steven Dreher, Director of Solutions Architecture at Green House Data, discussed how to plan for shifting resource requirements, overcome challenges, and implement hybrid IT alongside your existing data center assets. Highlights included anticipating workload, cost and resource calculations, integrating services on both sides...
"We're a cybersecurity firm that specializes in engineering security solutions both at the software and hardware level. Security cannot be an after-the-fact afterthought, which is what it's become," stated Richard Blech, Chief Executive Officer at Secure Channels, in this SYS-CON.tv interview at @ThingsExpo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
According to Forrester Research, every business will become either a digital predator or digital prey by 2020. To avoid demise, organizations must rapidly create new sources of value in their end-to-end customer experiences. True digital predators also must break down information and process silos and extend digital transformation initiatives to empower employees with the digital resources needed to win, serve, and retain customers.
The WebRTC Summit New York, to be held June 6-8, 2017, at the Javits Center in New York City, NY, announces that its Call for Papers is now open. Topics include all aspects of improving IT delivery by eliminating waste through automated business models leveraging cloud technologies. WebRTC Summit is co-located with 20th International Cloud Expo and @ThingsExpo. WebRTC is the future of browser-to-browser communications, and continues to make inroads into the traditional, difficult, plug-in web co...
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
The Internet of Things (IoT) promises to simplify and streamline our lives by automating routine tasks that distract us from our goals. This promise is based on the ubiquitous deployment of smart, connected devices that link everything from industrial control systems to automobiles to refrigerators. Unfortunately, comparatively few of the devices currently deployed have been developed with an eye toward security, and as the DDoS attacks of late October 2016 have demonstrated, this oversight can ...