Solving Java Out of Memory Issues in Kafka-Powered Microservices

by | Jan 19, 2025 | Big Data, DevOps, Java

Solving Java Out of Memory Issues in Kafka-Powered Microservices What happens when a Kafka-driven Java microservice crashes repeatedly after hours of operation, failing to complete its tasks? In our project, we faced exactly this scenario: recurring Out of Memory errors. Although the problem initially seemed straightforward, our investigation revealed a complex interaction between Java Heap, Non-Heap memory, thread management, and Kubernetes memory limits. Here’s how we solved the issue and the key lessons we learned along the way.

The Problem: Why Our Kafka-Powered Microservice Kept Crashing

We designed the microservice to process data streams from a Kafka topic and store the data in a local disk cache optimized for reading. Despite its robust design, the service terminated abruptly with Out of Memory errors after several hours of runtime. These crashes disrupted data processing and introduced the risk of potential data loss. The process exited silently to complicate matters, leaving no meaningful logs or error messages. We had to uncover the root cause quickly to restore stability.

The First Hypothesis: A Memory Leak in the Heap

With 13 GB of allocated Java Heap memory, we initially suspected a heap memory leak. We focused our debugging efforts on identifying objects retained in memory longer than necessary. However, the findings surprised us:
  • The codebase showed no signs of memory leaks.
  • Memory dumps from local environments and Kubernetes containers confirmed that no objects lingered unnecessarily.
  • Third-party libraries didn’t exhibit suspicious behavior.
The Heap seemed fine, yet the process kept crashing. This forced us to question our assumptions and look beyond the Heap.

Kubernetes Memory Limits: The Key to Understanding Out of Memory Errors

A Kubernetes operator provided a critical clue: the Out of Memory error didn’t originate from the Java Heap but ratherfrom the operating system. Kubernetes had capped the container’s memory at 16 GB, and here’s how the memory was allocated:
  • 13 GB went to the Java Heap (set by -Xmx and -Xms).
  • Only 3 GB remained for Non-Heap memory and other system resources.
This insight shifted our focus. Java requires more than just Heap memory to operate. The JVM also relies on Non-Heap memory for:
  • Metaspace, which stores class definitions.
  • Thread stacks, allocated for each thread.
  • Temporary memory spikes during Garbage Collection (GC).
We realized that GC spikes temporarily increased Non-Heap memory usage, pushing the total memory consumption beyond the 16 GB limit. As a result, the operating system terminated the process. This discovery explained the silent crashes with no Java logs.

Thread Management in Java: The Hidden Culprit

Reducing the Java Heap size allowed the service to run longer but didn’t fully resolve the crashes. Occasionally, we also encountered Out of Heap Space errors. These overlapping issues pointed to a deeper problem. By examining metrics in JConsole and Grafana, we identified a critical pattern. The number of threads grew steadily during runtime, eventually exceeding several hundred. Each thread consumed:
  • Stack memory in the Non-Heap area.
  • CPU resources, which created a bottleneck as the thread count increased.
When we reviewed the code, we discovered the issue. A Kafka listener created a new thread for every data stream it processed. These threads:
  • Repeatedly processed the same Kafka topic data.
  • Deserialized large numbers of objects, creating additional pressure on the Garbage Collector.
  • Consumed significant CPU time, slowing down the entire system.
This unbounded thread creation increased Non-Heap memory usage, filled the Heap with temporary objects, and triggered excessive GC activity. The system spiraled into instability, ultimately leading to crashes.

How We Fixed Java Memory Issues: Key Steps and Lessons

Once we identified the root causes, we implemented the following changes to stabilize the system:

1. Controlling Thread Creation

We limited the number of threads the Kafka listener could create and reused threads instead of constantly spawning new ones.

2. Optimizing Memory Allocation

We further reduced the Java Heap size to balance Heap and Non-Heap memory usage. At the same time, we increased the Kubernetes memory limit to provide more headroom for GC and threads.

3. Monitoring Metrics Continuously

We configured JConsole and a metrics exporter to provide real-time visibility into thread counts, GC activity, and memory usage in Grafana. This proactive monitoring helped us quickly detect and address anomalies.

4. Improving Garbage Collection

We fine-tuned GC settings to handle the workload more effectively, ensuring enough Non-Heap memory for temporary spikes during garbage collection.

Lessons Every Java Developer Should Know

1. Out of Memory Errors Go Beyond the Heap

Not all out-of-memory errors come from the Java Heap. Non-heap memory (e.g., thread stacks, and Metaspace) plays a critical role in JVM stability.

2. Understand Container Memory Limits

In Kubernetes or any containerized environment, Heap and Non-Heap memory must fit within the container’s memory limits. Mismanaging this balance can lead to crashes and instability.

3. Use Threads Wisely

Threads are a finite resource. Creating too many threads consumes memory, CPU cycles, and other system resources. Always limit and monitor thread creation.

4. Monitor and Tune the JVM

Tools like JConsole and Grafana can be used to monitor JVM performance. Review memory usage, thread counts, and GC behavior regularly to identify potential issues early.

5. Balance Memory Allocations

Avoid allocating an oversized Heap. Large Heaps can starve Non-Heap memory, leading to GC inefficiencies and system crashes. Achieving the right balance is key to maintaining stability.

Conclusion: Why Java Memory Problems Are Complex

Our journey revealed that Java memory management goes far beyond simply allocating a large Heap. Threads, Non-Heap memory, and Garbage Collection play vital roles in ensuring system stability. By addressing these factors, we resolved the issue and improved the performance of our Kafka-powered microservice.

Have you faced similar Java memory challenges? Share your experiences in the comments – we’d love to learn from your insights!

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