Upgrading to JDK 17 with ZGC: Performance Comparison and Migration Guide

The pause times of traditional garbage collectors such as CMS and G1 are a major pain point for latency‑sensitive services, often reaching tens or hundreds of milliseconds. ZGC, introduced experimentally in JDK 11 and production‑ready since JDK 15, aims to solve this by offering sub‑10 ms pauses and supporting heap sizes from 8 MB to 16 TB.

1.1 Irrefutable reasons to upgrade to JDK 17 include the need for millisecond‑level GC latency, better Spring Boot support, JIT improvements, new language features (sealed classes, pattern matching, records), and enhanced security patches.

1.2 Applicable scenarios are gateway services and Web APIs, while batch jobs, scheduled tasks, and CPU‑intensive workloads are not recommended.

2.1 GC time comparison shows ZGC achieving sub‑1 ms pauses compared to the much longer pauses of CMS, Parallel GC, and G1, as illustrated by the included chart.

2.2 CPU usage comparison indicates that the same workload on JDK 17 consumes about 10‑20 % more CPU than on JDK 8.

2. Upgrade method

3.1 Installing JDK 17

# ubuntu install jdk17
sudo apt install openjdk-17-jdk

# docker base images
docker pull openjdk:17-slim
docker pull openjdk:17-jdk-oraclelinux7
FROM openjdk:17-slim

3.2 JVM parameter adjustments for ZGC

--add-opens=java.base/java.lang=ALL-UNNAMED \
-Xms1500m -Xmx1500m \
-XX:ReservedCodeCacheSize=256m \
-XX:InitialCodeCacheSize=256m \
-XX:+UnlockExperimentalVMOptions \
-XX:+UseZGC \
-XX:ConcGCThreads=1 -XX:ParallelGCThreads=2 \
-XX:ZCollectionInterval=30 -XX:ZAllocationSpikeTolerance=5 \
-XX:+UnlockDiagnosticVMOptions -XX:-ZProactive \
-Xlog:safepoint,classhisto*=trace,age*,gc*=info:file=/opt/gc-%t.log:time,tid,tags:filecount=5,filesize=50m \
-XX:+HeapDumpOnOutOfMemoryError \
-XX:HeapDumpPath=/opt/errorDump.hprof

For comparison, the G1 configuration used was:

-Xmx3500m -Xms3500m -XX:+UseG1GC -XX:MaxGCPauseMillis=100
-XX:G1ReservePercent=10 -XX:ConcGCThreads=2 -XX:ParallelGCThreads=5
-XX:G1HeapRegionSize=16m -XX:MaxTenuringThreshold=14
-XX:SurvivorRatio=8

Both configurations were tested on a production machine handling 1500 TPS. The results demonstrate that ZGC can keep JVM‑level pauses under 1 ms, which is essential for low‑latency requirements.

References: https://tech.meituan.com/2020/08/06/new-zgc-practice-in-meituan.html https://tech.dewu.com/article?id=59