专栏目录
- 是时候升级java11了-01-jdk11优势和jdk选择
- 是时候升级java11了-02-升级jdk11踩坑记
- 是时候升级java11了-03虚拟机Jvm参数设置
- 是时候升级java11了-04微服务内http2通信之http2 Clear Text（h2c）
- 是时候升级java11了-05微服务内h2c通信的阻碍和问题解决
前言
紧接前2篇文章，我们今天来聊聊升级 Java11 之后的一写 Jvm 参数变化。Java11 删除掉了 cms 垃圾回收器，如果你升级到了 Java11 但是 Jvm 参数仍然使用 cms 垃圾回收器参数时控制台会报错，甚至会启动失败。
OpenJDK 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release.
Unrecognized VM option 'ParallelCMSThreads=2'
Did you mean 'ParallelGCThreads=<value>'? Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.JAVA11 JVM 启动参数
G1GC 配置项：
| Option and Default Value | Description |
|---|---|
| -XX:+UseG1GC | Use the Garbage First (G1) Collector |
| -XX:MaxGCPauseMillis=n | Sets a target for the maximum GC pause time. This is a soft goal, and the JVM will make its best effort to achieve it. |
| -XX:InitiatingHeapOccupancyPercent=n | Percentage of the (entire) heap occupancy to start a concurrent GC cycle. It is used by GCs that trigger a concurrent GC cycle based on the occupancy of the entire heap, not just one of the generations (e.g., G1). A value of 0 denotes 'do constant GC cycles'. The default value is 45. |
| -XX:NewRatio=n | Ratio of old/new generation sizes. The default value is 2. |
| -XX:SurvivorRatio=n | Ratio of eden/survivor space size. The default value is 8. |
| -XX:MaxTenuringThreshold=n | Maximum value for tenuring threshold. The default value is 15. |
| -XX:ParallelGCThreads=n | Sets the number of threads used during parallel phases of the garbage collectors. The default value varies with the platform on which the JVM is running. |
| -XX:ConcGCThreads=n | Number of threads concurrent garbage collectors will use. The default value varies with the platform on which the JVM is running. |
| -XX:G1ReservePercent=n | Sets the amount of heap that is reserved as a false ceiling to reduce the possibility of promotion failure. The default value is 10. |
| -XX:G1HeapRegionSize=n | With G1 the Java heap is subdivided into uniformly sized regions. This sets the size of the individual sub-divisions. The default value of this parameter is determined ergonomically based upon heap size. The minimum value is 1Mb and the maximum value is 32Mb. |
G1GC log 配置详细说明：
| G1GC | -Xlog:gc | Log messages with gc tag using info level to stdout, with default decorations. |
|---|---|---|
| G1GC | -Xlog:gc,safepoint | Log messages with either gc or safepoint tags (exclusive), both using 'info' level, to stdout, with default decorations. |
| G1GC | -Xlog:gc+ref=debug | Log messages with both gc and ref tags, using debug level, to stdout, with default decorations. |
| G1GC | -Xlog:gc=debug:file=gc.txt:none | Log messages with gc tag using debug level to file gc.txt with no decorations. |
| G1GC | -Xlog:gc=trace:file=gc.txt:uptimemillis, pids:filecount=5,filesize=1m | Log messages with gc tag using trace level to a rotating logs of 5 files of size 1MB, using the base name gc.txt, with uptimemillis and pid decorations. |
| G1GC | -Xlog:gc::uptime,tid | Log messages with gc tag using info level to output stdout, using uptime and tid decorations. |
| G1GC | -Xlog:gc*=info,safepoint*=off | Log messages with at least gc using info level, but turn off logging of messages tagged with safepoint. |
示例配置
-server
-Xmx4g
-Xms4g
-Xss256k
-XX:MaxDirectMemorySize=256m
-XX:+UseG1GC
-XX:+UseCompressedOops
-XX:+UseCompressedClassPointers
-XX:+SegmentedCodeCache
-verbose:gc
-XX:+PrintCommandLineFlags
-XX:+ExplicitGCInvokesConcurrent
-Djava.security.egd=file:/dev/./urandom
-Xlog:gc*,safepoint:/data/log/${SERVICE_NAME}/gc.log:time,uptime:filecount=100,filesize=50MG1GC 不必明确设置新生代大小，其自动调优也十分可靠，对于停顿时间往往在长时间运行后可以达到预期效果。
不建议进行过多的配置，对于 gc log 笔者认为还是很有必要，各位同学可以按照自己的实际需求进行配置。
声明
本系列文章由微服务核心组件mica作者如梦技术整理撰写，
如有参考或者转载，请保留原作者和注明出处。
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