jvm gc日志分析和工具
2024-06-09 01:29:14
目录
- Gc优化
- 垃圾收集发生的时机
- GC日志文件
- Parallel GC日志
- CMS日志
- G1日志
- Gc日志分析文件
- 在线gceasy
- pso-gc.log
- cms-gc.log
- g1-gc.log
- 离线GCviewer
- G1调优和优化指南
- 一、是否选择使用G1
- 二、开启G1
- 三、调优思路
- 1、试着增加内存
- 2、设置目标停顿时间
- 3、启动并发GC堆时内存占用百分比
- 四、最佳使用指南
- 官网建议
- 1、不要手动设置新生代和老年代的大小，只要设置整个堆的大小
- 2、不断调优暂停时间目标
- 3、使用-XX:ConcGCThreads=n来增加标记线程的数量
- 4、MixedGC调优
- 5、适当增加堆内存大小
Gc优化
内存被使用了之后，难免会有不够用或者达到设定值的时候，就需要对内存空间进行垃圾回收。
垃圾收集发生的时机
GC是由JVM自动完成的，根据JVM系统环境而定，所以时机是不确定的。 当然，我们可以手动进行垃圾回收，
比如调用System.gc()方法通知JVM进行一次垃圾回收，但是具体什么时刻运行也无法控制。也就是说
System.gc()只是通知要回收，什么时候回收由JVM决定。 但是不建议手动调用该方法，因为消耗的资源比较
大。
一般以下几种情况会发生垃圾回收
（1）当Eden区或者S区不够用了
（2）老年代空间不够用了
（3）方法区空间不够用了
（4）System.gc()
GC日志文件
基于java8分析
链接: https://pan.baidu.com/s/1rA7HtR2g-MNwzogv3ZJqeQ 提取码: p6ca
要想分析日志的信息，得先拿到GC日志文件才行，所以得先配置一下，之前也看过这些参数
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -Xloggc:gc.log
启动项目
Parallel GC日志
吞吐量优先
java8 默认使用Parallel Scavenge+Paralled Old
Java HotSpot(TM) 64-Bit Server VM (25.211-b12) for bsd-amd64 JRE (1.8.0_211-b12), built on Apr 1 2019 20:53:18 by "java_re" with gcc 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)
Memory: 4k page, physical 33554432k(1676620k free)/proc/meminfo:CommandLine flags: -XX:-BytecodeVerificationLocal -XX:-BytecodeVerificationRemote -XX:InitialHeapSize=536870912 -XX:+ManagementServer -XX:MaxHeapSize=8589934592 -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:TieredStopAtLevel=1 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseParallelGC
2022-01-11T19:08:46.032-0800: 1.593: [GC (Allocation Failure) [PSYoungGen: 131584K->13213K(153088K)] 131584K->13229K(502784K), 0.0149631 secs] [Times: user=0.03 sys=0.00, real=0.01 secs]
2022-01-11T19:08:46.114-0800: 1.674: [GC (Metadata GC Threshold) [PSYoungGen: 27621K->5732K(153088K)] 27637K->5756K(502784K), 0.0068344 secs] [Times: user=0.03 sys=0.00, real=0.01 secs]
2022-01-11T19:08:46.121-0800: 1.681: [Full GC (Metadata GC Threshold) [PSYoungGen: 5732K->0K(153088K)] [ParOldGen: 24K->5583K(167936K)] 5756K->5583K(321024K), [Metaspace: 20603K->20603K(1067008K)], 0.0241968 secs] [Times: user=0.08 sys=0.01, real=0.02 secs]
2022-01-11T19:08:47.061-0800: 2.621: [GC (Allocation Failure) [PSYoungGen: 131584K->12344K(153088K)] 137167K->17936K(321024K), 0.0064436 secs] [Times: user=0.03 sys=0.00, real=0.00 secs]
2022-01-11T19:08:48.485-0800: 4.045: [GC (Allocation Failure) [PSYoungGen: 143928K->17945K(237056K)] 149520K->23608K(404992K), 0.0140764 secs] [Times: user=0.04 sys=0.01, real=0.01 secs]
2022-01-11T19:08:49.315-0800: 4.875: [GC (Metadata GC Threshold) [PSYoungGen: 174411K->21496K(242688K)] 180074K->28179K(410624K), 0.0172624 secs] [Times: user=0.05 sys=0.02, real=0.02 secs]
2022-01-11T19:08:49.332-0800: 4.892: [Full GC (Metadata GC Threshold) [PSYoungGen: 21496K->0K(242688K)] [ParOldGen: 6682K->25984K(262656K)] 28179K->25984K(505344K), [Metaspace: 33869K->33869K(1079296K)], 0.0925447 secs] [Times: user=0.31 sys=0.02, real=0.09 secs]
HeapPSYoungGen total 242688K, used 59499K [0x0000000715580000, 0x000000072e780000, 0x00000007c0000000)eden space 221184K, 26% used [0x0000000715580000,0x0000000718f9aef0,0x0000000722d80000)from space 21504K, 0% used [0x0000000722d80000,0x0000000722d80000,0x0000000724280000)to space 26112K, 0% used [0x000000072ce00000,0x000000072ce00000,0x000000072e780000)ParOldGen total 262656K, used 25984K [0x00000005c0000000, 0x00000005d0080000, 0x0000000715580000)object space 262656K, 9% used [0x00000005c0000000,0x00000005c1960270,0x00000005d0080000)Metaspace used 35271K, capacity 36842K, committed 36992K, reserved 1081344Kclass space used 4848K, capacity 5147K, committed 5248K, reserved 1048576K注意 如果回收的差值中间有出入，说明这部分空间是Old区释放出来的
CMS日志
【停顿时间优先】
参数设置：-XX:+UseConcMarkSweepGC -Xloggc:cms-gc.log
使用 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC
Java HotSpot(TM) 64-Bit Server VM (25.211-b12) for bsd-amd64 JRE (1.8.0_211-b12), built on Apr 1 2019 20:53:18 by "java_re" with gcc 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)
Memory: 4k page, physical 33554432k(940564k free)/proc/meminfo:CommandLine flags: -XX:-BytecodeVerificationLocal -XX:-BytecodeVerificationRemote -XX:InitialHeapSize=536870912 -XX:+ManagementServer -XX:MaxHeapSize=8589934592 -XX:MaxNewSize=697933824 -XX:MaxTenuringThreshold=6 -XX:OldPLABSize=16 -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:TieredStopAtLevel=1 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:+UseParNewGC
2022-01-11T19:14:54.684-0800: 1.418: [GC (Allocation Failure) 2022-01-11T19:14:54.684-0800: 1.418: [ParNew: 139776K->13890K(157248K), 0.0127240 secs] 139776K->13890K(506816K), 0.0129656 secs] [Times: user=0.04 sys=0.01, real=0.01 secs]
2022-01-11T19:14:54.698-0800: 1.431: [GC (CMS Initial Mark) [1 CMS-initial-mark: 0K(349568K)] 16686K(506816K), 0.0023723 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
2022-01-11T19:14:54.700-0800: 1.433: [CMS-concurrent-mark-start]
2022-01-11T19:14:54.701-0800: 1.434: [CMS-concurrent-mark: 0.001/0.001 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
2022-01-11T19:14:54.701-0800: 1.434: [CMS-concurrent-preclean-start]
2022-01-11T19:14:54.703-0800: 1.436: [CMS-concurrent-preclean: 0.002/0.002 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
2022-01-11T19:14:54.703-0800: 1.437: [CMS-concurrent-abortable-preclean-start]
2022-01-11T19:14:55.111-0800: 1.845: [CMS-concurrent-abortable-preclean: 0.170/0.408 secs] [Times: user=0.79 sys=0.08, real=0.41 secs]
2022-01-11T19:14:55.112-0800: 1.845: [GC (CMS Final Remark) [YG occupancy: 86083 K (157248 K)]2022-01-11T19:14:55.112-0800: 1.845: [Rescan (parallel) , 0.0087525 secs]2022-01-11T19:14:55.120-0800: 1.854: [weak refs processing, 0.0000350 secs]2022-01-11T19:14:55.120-0800: 1.854: [class unloading, 0.0019295 secs]2022-01-11T19:14:55.122-0800: 1.856: [scrub symbol table, 0.0026388 secs]2022-01-11T19:14:55.125-0800: 1.858: [scrub string table, 0.0003238 secs][1 CMS-remark: 0K(349568K)] 86083K(506816K), 0.0144971 secs] [Times: user=0.06 sys=0.01, real=0.01 secs]
2022-01-11T19:14:55.126-0800: 1.860: [CMS-concurrent-sweep-start]
2022-01-11T19:14:55.126-0800: 1.860: [CMS-concurrent-sweep: 0.000/0.000 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
2022-01-11T19:14:55.126-0800: 1.860: [CMS-concurrent-reset-start]
2022-01-11T19:14:55.185-0800: 1.919: [CMS-concurrent-reset: 0.059/0.059 secs] [Times: user=0.10 sys=0.03, real=0.06 secs]
2022-01-11T19:14:55.571-0800: 2.304: [GC (Allocation Failure) 2022-01-11T19:14:55.571-0800: 2.304: [ParNew: 153666K->13538K(157248K), 0.0272992 secs] 153666K->18672K(506816K), 0.0275117 secs] [Times: user=0.10 sys=0.02, real=0.02 secs]
2022-01-11T19:14:56.965-0800: 3.698: [GC (Allocation Failure) 2022-01-11T19:14:56.965-0800: 3.698: [ParNew: 153314K->15291K(157248K), 0.0122546 secs] 158448K->26026K(506816K), 0.0127318 secs] [Times: user=0.06 sys=0.01, real=0.01 secs]
2022-01-11T19:14:57.683-0800: 4.416: [GC (Allocation Failure) 2022-01-11T19:14:57.683-0800: 4.416: [ParNew: 155067K->10713K(157248K), 0.0128050 secs] 165802K->30489K(506816K), 0.0129698 secs] [Times: user=0.06 sys=0.01, real=0.01 secs]
Heappar new generation total 157248K, used 49453K [0x00000005c0000000, 0x00000005caaa0000, 0x00000005e9990000)eden space 139776K, 27% used [0x00000005c0000000, 0x00000005c25d5010, 0x00000005c8880000)from space 17472K, 61% used [0x00000005c8880000, 0x00000005c92f6708, 0x00000005c9990000)to space 17472K, 0% used [0x00000005c9990000, 0x00000005c9990000, 0x00000005caaa0000)concurrent mark-sweep generation total 349568K, used 19775K [0x00000005e9990000, 0x00000005feef0000, 0x00000007c0000000)Metaspace used 35335K, capacity 36896K, committed 37220K, reserved 1081344Kclass space used 4845K, capacity 5146K, committed 5220K, reserved 1048576KG1日志
【停顿时间优先】
参数设置：-XX:+UseG1GC -Xloggc:g1-gc.log
理解G1日志格式：
https://blogs.oracle.com/poonam/understanding-g1-gc-logs
https://blog.gceasy.io/2016/07/07/understanding-g1-gc-log-format/ 这篇文章推荐读一下
Java HotSpot(TM) 64-Bit Server VM (25.211-b12) for bsd-amd64 JRE (1.8.0_211-b12), built on Apr 1 2019 20:53:18 by "java_re" with gcc 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)
Memory: 4k page, physical 33554432k(714396k free)/proc/meminfo:CommandLine flags: -XX:-BytecodeVerificationLocal -XX:-BytecodeVerificationRemote -XX:InitialHeapSize=536870912 -XX:+ManagementServer -XX:MaxHeapSize=8589934592 -XX:+PrintGC -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:TieredStopAtLevel=1 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC
2022-01-11T19:17:51.920-0800: 1.361: [GC pause (G1 Evacuation Pause) (young), 0.0057847 secs][Parallel Time: 3.4 ms, GC Workers: 8][GC Worker Start (ms): Min: 1361.7, Avg: 1361.8, Max: 1362.2, Diff: 0.5][Ext Root Scanning (ms): Min: 0.0, Avg: 0.6, Max: 2.9, Diff: 2.9, Sum: 4.8][Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0][Processed Buffers: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0][Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0][Code Root Scanning (ms): Min: 0.0, Avg: 0.1, Max: 0.6, Diff: 0.6, Sum: 1.1][Object Copy (ms): Min: 0.0, Avg: 1.9, Max: 2.4, Diff: 2.4, Sum: 15.4][Termination (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 1.0][Termination Attempts: Min: 1, Avg: 21.0, Max: 34, Diff: 33, Sum: 168][GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1][GC Worker Total (ms): Min: 2.4, Avg: 2.8, Max: 2.9, Diff: 0.6, Sum: 22.4][GC Worker End (ms): Min: 1364.6, Avg: 1364.6, Max: 1364.6, Diff: 0.1][Code Root Fixup: 0.0 ms][Code Root Purge: 0.0 ms][Clear CT: 0.1 ms][Other: 2.3 ms][Choose CSet: 0.0 ms][Ref Proc: 1.9 ms][Ref Enq: 0.0 ms][Redirty Cards: 0.1 ms][Humongous Register: 0.0 ms][Humongous Reclaim: 0.0 ms][Free CSet: 0.0 ms][Eden: 24.0M(24.0M)->0.0B(36.0M) Survivors: 0.0B->4096.0K Heap: 24.0M(512.0M)->3855.6K(512.0M)][Times: user=0.02 sys=0.00, real=0.00 secs]
2022-01-11T19:17:52.124-0800: 1.566: [GC pause (G1 Evacuation Pause) (young), 0.0076186 secs][Parallel Time: 4.1 ms, GC Workers: 8][GC Worker Start (ms): Min: 1566.0, Avg: 1566.2, Max: 1566.6, Diff: 0.5][Ext Root Scanning (ms): Min: 0.0, Avg: 0.4, Max: 1.4, Diff: 1.4, Sum: 3.3][Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0][Processed Buffers: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0][Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0][Code Root Scanning (ms): Min: 0.0, Avg: 0.1, Max: 0.5, Diff: 0.5, Sum: 0.7][Object Copy (ms): Min: 1.9, Avg: 2.8, Max: 3.7, Diff: 1.8, Sum: 22.4][Termination (ms): Min: 0.0, Avg: 0.6, Max: 0.7, Diff: 0.7, Sum: 4.7][Termination Attempts: Min: 1, Avg: 23.2, Max: 45, Diff: 44, Sum: 186][GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1][GC Worker Total (ms): Min: 3.5, Avg: 3.9, Max: 4.0, Diff: 0.5, Sum: 31.2][GC Worker End (ms): Min: 1570.0, Avg: 1570.0, Max: 1570.1, Diff: 0.1][Code Root Fixup: 0.0 ms][Code Root Purge: 0.0 ms][Clear CT: 0.1 ms][Other: 3.4 ms][Choose CSet: 0.0 ms][Ref Proc: 3.0 ms][Ref Enq: 0.0 ms][Redirty Cards: 0.1 ms][Humongous Register: 0.0 ms][Humongous Reclaim: 0.0 ms][Free CSet: 0.0 ms][Eden: 36.0M(36.0M)->0.0B(300.0M) Survivors: 4096.0K->6144.0K Heap: 39.8M(512.0M)->8414.5K(512.0M)][Times: user=0.03 sys=0.01, real=0.01 secs]
2022-01-11T19:17:52.480-0800: 1.921: [GC pause (Metadata GC Threshold) (young) (initial-mark), 0.0117597 secs][Parallel Time: 7.1 ms, GC Workers: 8][GC Worker Start (ms): Min: 1921.2, Avg: 1921.5, Max: 1922.3, Diff: 1.1][Ext Root Scanning (ms): Min: 1.6, Avg: 2.3, Max: 2.7, Diff: 1.1, Sum: 18.8][Update RS (ms): Min: 0.0, Avg: 0.1, Max: 0.3, Diff: 0.3, Sum: 0.9][Processed Buffers: Min: 0, Avg: 0.5, Max: 1, Diff: 1, Sum: 4][Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0][Code Root Scanning (ms): Min: 0.0, Avg: 0.2, Max: 0.7, Diff: 0.7, Sum: 1.6][Object Copy (ms): Min: 3.3, Avg: 3.8, Max: 4.3, Diff: 1.0, Sum: 30.1][Termination (ms): Min: 0.0, Avg: 0.3, Max: 0.4, Diff: 0.4, Sum: 2.5][Termination Attempts: Min: 1, Avg: 1.1, Max: 2, Diff: 1, Sum: 9][GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1][GC Worker Total (ms): Min: 5.9, Avg: 6.7, Max: 7.0, Diff: 1.1, Sum: 54.0][GC Worker End (ms): Min: 1928.1, Avg: 1928.2, Max: 1928.3, Diff: 0.2][Code Root Fixup: 0.1 ms][Code Root Purge: 0.0 ms][Clear CT: 0.2 ms][Other: 4.4 ms][Choose CSet: 0.0 ms][Ref Proc: 3.9 ms][Ref Enq: 0.1 ms][Redirty Cards: 0.1 ms][Humongous Register: 0.0 ms][Humongous Reclaim: 0.0 ms][Free CSet: 0.1 ms][Eden: 66.0M(300.0M)->0.0B(292.0M) Survivors: 6144.0K->14.0M Heap: 73.2M(512.0M)->15.5M(512.0M)][Times: user=0.04 sys=0.01, real=0.01 secs]
2022-01-11T19:17:52.492-0800: 1.933: [GC concurrent-root-region-scan-start]
2022-01-11T19:17:52.497-0800: 1.938: [GC concurrent-root-region-scan-end, 0.0051380 secs]
2022-01-11T19:17:52.497-0800: 1.938: [GC concurrent-mark-start]
2022-01-11T19:17:52.497-0800: 1.939: [GC concurrent-mark-end, 0.0005947 secs]
2022-01-11T19:17:52.497-0800: 1.939: [GC remark 2022-01-11T19:17:52.498-0800: 1.939: [Finalize Marking, 0.0007418 secs] 2022-01-11T19:17:52.498-0800: 1.940: [GC ref-proc, 0.0000878 secs] 2022-01-11T19:17:52.498-0800: 1.940: [Unloading, 0.0019575 secs], 0.0031669 secs][Times: user=0.01 sys=0.00, real=0.01 secs]
2022-01-11T19:17:52.501-0800: 1.942: [GC cleanup 17M->17M(512M), 0.0007957 secs][Times: user=0.01 sys=0.00, real=0.00 secs]
2022-01-11T19:17:52.502-0800: 1.943: [GC concurrent-cleanup-start]
2022-01-11T19:17:52.502-0800: 1.943: [GC concurrent-cleanup-end, 0.0000174 secs]
2022-01-11T19:17:55.118-0800: 4.560: [GC pause (G1 Evacuation Pause) (young) (initial-mark), 0.0368034 secs][Parallel Time: 23.9 ms, GC Workers: 8][GC Worker Start (ms): Min: 4559.9, Avg: 4560.0, Max: 4560.0, Diff: 0.2][Ext Root Scanning (ms): Min: 1.3, Avg: 1.7, Max: 2.2, Diff: 0.8, Sum: 13.3][Update RS (ms): Min: 0.0, Avg: 0.4, Max: 2.2, Diff: 2.2, Sum: 2.9][Processed Buffers: Min: 0, Avg: 0.6, Max: 2, Diff: 2, Sum: 5][Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1][Code Root Scanning (ms): Min: 0.0, Avg: 1.0, Max: 2.8, Diff: 2.8, Sum: 8.3][Object Copy (ms): Min: 18.5, Avg: 19.9, Max: 21.2, Diff: 2.7, Sum: 159.1][Termination (ms): Min: 0.0, Avg: 0.7, Max: 0.9, Diff: 0.9, Sum: 5.3][Termination Attempts: Min: 1, Avg: 12.1, Max: 23, Diff: 22, Sum: 97][GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1][GC Worker Total (ms): Min: 23.4, Avg: 23.6, Max: 23.8, Diff: 0.4, Sum: 189.1][GC Worker End (ms): Min: 4583.4, Avg: 4583.6, Max: 4583.7, Diff: 0.3][Code Root Fixup: 0.2 ms][Code Root Purge: 0.0 ms][Clear CT: 0.2 ms][Other: 12.4 ms][Choose CSet: 0.0 ms][Ref Proc: 11.0 ms][Ref Enq: 0.1 ms][Redirty Cards: 0.1 ms][Humongous Register: 0.0 ms][Humongous Reclaim: 0.0 ms][Free CSet: 1.0 ms][Eden: 292.0M(292.0M)->0.0B(270.0M) Survivors: 14.0M->36.0M Heap: 307.3M(512.0M)->37.0M(512.0M)][Times: user=0.09 sys=0.02, real=0.04 secs]
2022-01-11T19:17:55.155-0800: 4.597: [GC concurrent-root-region-scan-start]
2022-01-11T19:17:55.168-0800: 4.610: [GC concurrent-root-region-scan-end, 0.0130025 secs]
2022-01-11T19:17:55.168-0800: 4.610: [GC concurrent-mark-start]
2022-01-11T19:17:55.169-0800: 4.610: [GC concurrent-mark-end, 0.0001416 secs]
2022-01-11T19:17:55.169-0800: 4.610: [GC remark 2022-01-11T19:17:55.169-0800: 4.610: [Finalize Marking, 0.0009400 secs] 2022-01-11T19:17:55.170-0800: 4.611: [GC ref-proc, 0.0001618 secs] 2022-01-11T19:17:55.170-0800: 4.612: [Unloading, 0.0028892 secs], 0.0044676 secs][Times: user=0.02 sys=0.00, real=0.01 secs]
2022-01-11T19:17:55.173-0800: 4.615: [GC cleanup 39M->39M(512M), 0.0006256 secs][Times: user=0.01 sys=0.00, real=0.00 secs]
Heapgarbage-first heap total 524288K, used 189423K [0x00000005c0000000, 0x00000005c0200800, 0x00000007c0000000)region size 2048K, 93 young (190464K), 18 survivors (36864K)Metaspace used 35233K, capacity 36838K, committed 36992K, reserved 1081344Kclass space used 4849K, capacity 5147K, committed 5248K, reserved 1048576K
Gc日志分析文件
在线gceasy
官网：https://gceasy.io
可以比较不同的垃圾收集器的吞吐量和停顿时间
比如打开cms-gc.log和g1-gc.log
pso-gc.log
-XX:+UseParallelGC
https://gceasy.ycrash.cn/my-gc-report.jsp?p=c2hhcmVkLzIwMjIvMDEvMTEvLS1wc28tZ2MubG9nLS0xMS0zMy00OQ==&channel=WEB
cms-gc.log
https://gceasy.ycrash.cn/my-gc-report.jsp?p=c2hhcmVkLzIwMjIvMDEvMTEvLS1jbXMtZ2MubG9nLS0xMS0zMS01&channel=WEB
g1-gc.log
https://gceasy.io/my-gc-report.jsp?p=c2hhcmVkLzIwMjIvMDEvMTEvLS1nMS1nYy5sb2ctLTExLTI2LTQ2&channel=WEB
- 内存占用
- 停顿时间
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离线GCviewer
下载，解压，idea打开。执行mvn clean install ，找到/target/gcviewer-1.36.jar 打开
链接: https://pan.baidu.com/s/1rA7HtR2g-MNwzogv3ZJqeQ 提取码: p6ca
G1调优和优化指南
一、是否选择使用G1
是否选用G1垃圾收集器的判断依据 jdk9默认G1
https://docs.oracle.com/javase/8/docs/technotes/guides/vm/G1.html#use_cases
- 50%以上的堆被存活对象占用
- 对象分配和晋升的速度变化非常大
- 垃圾回收时间比较长
- 适合大内存（6G以上，不要低于4g） ，多核
二、开启G1
使用G1GC垃圾收集器: -XX:+UseG1GC
修改配置参数，获取到gc日志，使用GCViewer分析吞吐量和响应时间
三、调优思路
1、试着增加内存
一般内存不够，第一反应是试着增加内存看看，要不断的去尝试，是很枯燥的
比如设置堆内存的大小，获取到gc日志，使用GCViewer分析吞吐量和响应时间
-XX:MetaspaceSize=100M
-Xms300M
-Xmx300M
2、设置目标停顿时间
G1主打的就是可以自定义最大停顿时间,设置最大停顿时间，获取到gc日志，使用GCViewer分析吞吐量和响应时间
-XX:MaxGCPauseMillis=20 设置最大GC停顿时间指标
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3、启动并发GC堆时内存占用百分比
-XX:InitiatingHeapOccupancyPercent=45 G1用它来触发并发GC周期,基于整个堆的使用率,而不只是某一代内存的 使用比例。值为 0 则表示“一直执行GC循环)'. 默认值为 45 (例如, 全部的 45% 或者使用了45%).
四、最佳使用指南
官网建议
https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/g1_gc_tuning.html#recommendations
1、不要手动设置新生代和老年代的大小，只要设置整个堆的大小
G1收集器在运行过程中，会自己调整新生代和老年代的大小
其实是通过adapt代的大小来调整对象晋升的速度和年龄，从而达到为收集器设置的暂停时间目标
如果手动设置了大小就意味着放弃了G1的自动调优
2、不断调优暂停时间目标
一般情况下这个值设置到100ms或者200ms都是可以的(不同情况下会不一样)，但如果设置成50ms就不太合理。暂停
时间设置的太短，就会导致出现G1跟不上垃圾产生的速度。最终退化成Full GC。所以对这个参数的调优是一个持续
的过程，逐步调整到最佳状态。暂停时间只是一个目标，并不能总是得到满足。
3、使用-XX:ConcGCThreads=n来增加标记线程的数量
IHOP如果阀值设置过高，可能会遇到转移失败的风险，比如对象进行转移时空间不足。如果阀值设置过低，就会使标
记周期运行过于频繁，并且有可能混合收集期回收不到空间。
IHOP值如果设置合理，但是在并发周期时间过长时，可以尝试增加并发线程数，调高ConcGCThreads。
4、MixedGC调优
-XX:InitiatingHeapOccupancyPercent 用于更改标记阈值。
-XX:G1MixedGCLiveThresholdPercent 用于更改混合垃圾收集决策。
-XX:G1MixedGCCountTarger -XX:G1OldCSetRegionThresholdPercent 用于调整旧区域的 CSet。
5、适当增加堆内存大小
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