Welcome!

Apache Authors: Pat Romanski, Liz McMillan, Elizabeth White, Janakiram MSV, Gil Allouche

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
SYS-CON Events announced today the Enterprise IoT Bootcamp, being held November 1-2, 2016, in conjunction with 19th Cloud Expo | @ThingsExpo at the Santa Clara Convention Center in Santa Clara, CA. Combined with real-world scenarios and use cases, the Enterprise IoT Bootcamp is not just based on presentations but with hands-on demos and detailed walkthroughs. We will introduce you to a variety of real world use cases prototyped using Arduino, Raspberry Pi, BeagleBone, Spark, and Intel Edison. Y...
Complete Internet of Things (IoT) embedded device security is not just about the device but involves the entire product’s identity, data and control integrity, and services traversing the cloud. A device can no longer be looked at as an island; it is a part of a system. In fact, given the cross-domain interactions enabled by IoT it could be a part of many systems. Also, depending on where the device is deployed, for example, in the office building versus a factory floor or oil field, security ha...
Is your aging software platform suffering from technical debt while the market changes and demands new solutions at a faster clip? It’s a bold move, but you might consider walking away from your core platform and starting fresh. ReadyTalk did exactly that. In his General Session at 19th Cloud Expo, Michael Chambliss, Head of Engineering at ReadyTalk, will discuss why and how ReadyTalk diverted from healthy revenue and over a decade of audio conferencing product development to start an innovati...
Fifty billion connected devices and still no winning protocols standards. HTTP, WebSockets, MQTT, and CoAP seem to be leading in the IoT protocol race at the moment but many more protocols are getting introduced on a regular basis. Each protocol has its pros and cons depending on the nature of the communications. Does there really need to be only one protocol to rule them all? Of course not. In his session at @ThingsExpo, Chris Matthieu, co-founder and CTO of Octoblu, walk you through how Oct...
The Jevons Paradox suggests that when technological advances increase efficiency of a resource, it results in an overall increase in consumption. Writing on the increased use of coal as a result of technological improvements, 19th-century economist William Stanley Jevons found that these improvements led to the development of new ways to utilize coal. In his session at 19th Cloud Expo, Mark Thiele, Chief Strategy Officer for Apcera, will compare the Jevons Paradox to modern-day enterprise IT, e...
SYS-CON Events announced today that Bsquare has been named “Silver Sponsor” of SYS-CON's @ThingsExpo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. For more than two decades, Bsquare has helped its customers extract business value from a broad array of physical assets by making them intelligent, connecting them, and using the data they generate to optimize business processes.
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
There are several IoTs: the Industrial Internet, Consumer Wearables, Wearables and Healthcare, Supply Chains, and the movement toward Smart Grids, Cities, Regions, and Nations. There are competing communications standards every step of the way, a bewildering array of sensors and devices, and an entire world of competing data analytics platforms. To some this appears to be chaos. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, Bradley Holt, Developer Advocate a...
If you’re responsible for an application that depends on the data or functionality of various IoT endpoints – either sensors or devices – your brand reputation depends on the security, reliability, and compliance of its many integrated parts. If your application fails to deliver the expected business results, your customers and partners won't care if that failure stems from the code you developed or from a component that you integrated. What can you do to ensure that the endpoints work as expect...
So, you bought into the current machine learning craze and went on to collect millions/billions of records from this promising new data source. Now, what do you do with them? Too often, the abundance of data quickly turns into an abundance of problems. How do you extract that "magic essence" from your data without falling into the common pitfalls? In her session at @ThingsExpo, Natalia Ponomareva, Software Engineer at Google, provided tips on how to be successful in large scale machine learning...
In his general session at 18th Cloud Expo, Lee Atchison, Principal Cloud Architect and Advocate at New Relic, discussed cloud as a ‘better data center’ and how it adds new capacity (faster) and improves application availability (redundancy). The cloud is a ‘Dynamic Tool for Dynamic Apps’ and resource allocation is an integral part of your application architecture, so use only the resources you need and allocate /de-allocate resources on the fly.
If you had a chance to enter on the ground level of the largest e-commerce market in the world – would you? China is the world’s most populated country with the second largest economy and the world’s fastest growing market. It is estimated that by 2018 the Chinese market will be reaching over $30 billion in gaming revenue alone. Admittedly for a foreign company, doing business in China can be challenging. Often changing laws, administrative regulations and the often inscrutable Chinese Interne...
Enterprise IT has been in the era of Hybrid Cloud for some time now. But it seems most conversations about Hybrid are focused on integrating AWS, Microsoft Azure, or Google ECM into existing on-premises systems. Where is all the Private Cloud? What do technology providers need to do to make their offerings more compelling? How should enterprise IT executives and buyers define their focus, needs, and roadmap, and communicate that clearly to the providers?
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management solutions, helping companies worldwide activate their data to drive more value and business insight and to transform moder...
The many IoT deployments around the world are busy integrating smart devices and sensors into their enterprise IT infrastructures. Yet all of this technology – and there are an amazing number of choices – is of no use without the software to gather, communicate, and analyze the new data flows. Without software, there is no IT. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will look at the protocols that communicate data and the emerging data analy...
Digital innovation is the next big wave of business transformation based on digital technologies of which IoT and Big Data are key components, For example: Business boundary innovation is a challenge to excavate third-party business value using IoT and BigData, like Nest Business structure innovation may propose re-building business structure from scratch, as Uber does in the taxicab industry The social model innovation is also a big challenge to the new social architecture with the design fr...
Data is an unusual currency; it is not restricted by the same transactional limitations as money or people. In fact, the more that you leverage your data across multiple business use cases, the more valuable it becomes to the organization. And the same can be said about the organization’s analytics. In his session at 19th Cloud Expo, Bill Schmarzo, CTO for the Big Data Practice at EMC, will introduce a methodology for capturing, enriching and sharing data (and analytics) across the organizati...
There is little doubt that Big Data solutions will have an increasing role in the Enterprise IT mainstream over time. Big Data at Cloud Expo - to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA - has announced its Call for Papers is open. Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is...
IoT is fundamentally transforming the auto industry, turning the vehicle into a hub for connected services, including safety, infotainment and usage-based insurance. Auto manufacturers – and businesses across all verticals – have built an entire ecosystem around the Connected Car, creating new customer touch points and revenue streams. In his session at @ThingsExpo, Macario Namie, Head of IoT Strategy at Cisco Jasper, will share real-world examples of how IoT transforms the car from a static p...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 19th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo Silicon Valley Call for Papers is now open.