全面了解JVM执行过程的细节-最全GC日志参数
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最近老有朋友问我，GC日志的信息不全面，不够充分了解JVM执行过程，特别是GC时候的详细信息。
JDK1.8下GC最全日志配置方式
这个问题好办，直接把有用的JVM和GC信息都打印了就得了，参数见下：
java -Xmx4g -Xms4g -XX:+UseG1GC
-XX:ConcGCThreads=2 -XX:ParallelGCThreads=8
-XX:+UseStringDeduplication -XX:+ParallelRefProcEnabled
-XX:InitiatingHeapOccupancyPercent=45
-XX:MaxGCPauseMillis=200 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=8
-XX:+UnlockExperimentalVMOptions -XX:G1MixedGCLiveThresholdPercent=85
-XX:G1ReservePercent=10 -XX:G1HeapRegionSize=2m -XX:G1NewSizePercent=5
-XX:G1MaxNewSizePercent=60 -XX:G1OldCSetRegionThresholdPercent=10
-XX:+PrintCommandLineFlags -XX:+PrintAdaptiveSizePolicy
-XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails
-XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+PrintGCCause
-XX:+PrintPromotionFailure -XX:+PrintReferenceGC -XX:+PrintTenuringDistribution
-XX:+UnlockDiagnosticVMOptions -XX:+G1PrintHeapRegions
-XX:+PrintVMOptions -XX:+PrintTLAB -Xloggc:gc.log -jar gateway-server-0.0.1-SNAPSHOT.jar jdk8下执行，然后使用某种工具压测，比如wrk：wrk -d 120s http://localhost:8088/api/hello
最后看一下gc.log，你会发现跟你常见的gc日志，完全不一样，详细的一塌糊涂。
[G1Ergonomics (Mixed GCs) do not start mixed GCs, reason: candidate old regions not available]
G1HR #EndGC 能看到判断是否执行mixed gc
[SoftReference, 0 refs, 0.0005449 secs]2021-11-22T23:19:40.381-0800: 10.248:
[WeakReference, 1009 refs, 0.0002207 secs]2021-11-22T23:19:40.382-0800: 10.248:
[FinalReference, 63 refs, 0.0002413 secs]2021-11-22T23:19:40.382-0800: 10.249:
[PhantomReference, 0 refs, 11 refs, 0.0004593 secs]2021-11-22T23:19:40.382-0800: 10.2ref引用的数量
Desired survivor size 161480704 bytes, new threshold 15 (max 15)
- age 1: 69112 bytes, 69112 total
- age 2: 244616 bytes, 313728 total
- age 3: 3825312 bytes, 4139040 total
- age 4: 8959368 bytes, 13098408 total
- age 5: 327952 bytes, 13426360 total
- age 6: 3634808 bytes, 17061168 total各代的对象占用内存
14.208: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 0,
predicted base time: 14.03 ms, remaining time: 185.97 ms, target pause time: 200.00 ms]
14.208: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 1217 regions,
survivors: 11 regions, predicted young region time: 101.24 ms]
14.208: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 1217 regions,
survivors: 11 regions, old: 0 regions, predicted pause time: 115.27 ms,
target pause time: 200.00 ms]选择的CSet收集集数量，预测的处理时间等。
2022-09-26 update：
是不是还能加的更全？当然可以，还少了不少参数，比如safepoint相关的：
-XX:+PrintGCApplicationStoppedTime -XX:+PrintGCApplicationConcurrentTime
-XX:+PrintSafepointStatistics -XX:PrintSafepointStatisticsCount=1
-XX:PrintSafepointStatisticsTimeout=100 -XX:+SafepointTimeout -XX:SafepointTimeoutDelay=100 JDK11+下最全GC日志配置方式
待续...
编辑于 2022-09-26 20:20
