OS-Caused Large JVM Pauses: Investigations and Solutions

For customer-facing Java applications (e.g., online gaming and online chatting), ensuring low latencies is not just a preferred feature, but a must-have feature. Given the popularity and powerfulness of Java, a significant portion of today's backend services are implemented in Java. JVM (Java Virtual Machine) manages a heap space to hold application objects. The heap space can be frequently GC-ed (Garbage Collected), and applications can be occasionally stopped by JVM GC pauses. As a result, ensuring low JVM GC pauses is critical for business applications that have latency SLA (Service Level Agreements). In our production system, we found out that there are some (and large) JVM pauses cannot be explained by application-level activities and JVM activities during GC; instead, they are caused by OS mechanisms. In this work, we investigate the large JVM pauses caused by OS. We characterize various such problems into two scenarios. For both scenarios, we successfully root-cause the reasons and propose solutions. The findings can be used to mitigate the long JVM pauses and enhance JVM implementations. We share the knowledge and experiences in this writing.