一、GCViewer介绍

业界较为流行分析GC日志的两个工具——GCViewer、GCEasy。GCEasy部分功能还是要收费的，今天笔者给大家介绍一下GCViewer的使用与功能点。Memory Analyzer Mat JVM 分析

二、GCViewer 使用

2.1 编译

GitHub - chewiebug/GCViewer at 1.36

首先，在github上搜索GCViewer项目，并下载到本地。GCViewer项目没有提供现成的release版本，利用如下maven编译命令即可完成GCViewer的编译工作，最终生成一个gcviewer-1.36.jar。

yum install  -y  git  svn  maven
cd  /hadoop/software/
unzip  GCViewer-1.36.zip
cd  GCViewer-1.36
## maven 编译 操作环境 Linux 
mvn clean install -DskipTests

2.2 使用

双击编译好的jar

Full GC Lines：（full gc）
Inc GC Lines：（增量GC）
GC Times Line：（gc 时间）
GC Times Rectangles：（gc时间区域）
Total Heap：(总堆大小)
Red line that shows heap size
Tenured Generation：（老年代）
Young Generation：（年轻代）
Used Heap：（堆使用量）
Initial mark level：（cms或g1垃圾回收算法初始标记事件）
Concurrent collections：（cms或g1垃圾回收并发收集周期）

运行Java程序打印下GC日志，垃圾收集器使用G1

/usr/java/jdk1.8.0_144/bin/java \
  -Xmx1024m -Xms1024m -XX:+UseG1GC -XX:MaxGCPauseMillis=100 \
  -XX:-ResizePLAB -verbose:gc -XX:-PrintGCCause -XX:+PrintAdaptiveSizePolicy \
  -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:/hadoop/datadir/windeploy/log/ETL/DS/gc.log-`date +'%Y%m%d%H%M'` \
  -classpath xxx.jar

在路径 /hadoop/datadir/windeploy/log/ETL/DS/ 就会产生gc日志，产生的部分日志如下：

2022-11-23T15:33:14.532+0800: 27253.342: [GC concurrent-root-region-scan-start]
2022-11-23T15:33:14.540+0800: 27253.350: [GC concurrent-root-region-scan-end, 0.0077278 secs]
2022-11-23T15:33:14.540+0800: 27253.350: [GC concurrent-mark-start]
2022-11-23T15:33:16.881+0800: 27255.691: [GC concurrent-mark-end, 2.3412370 secs]
2022-11-23T15:33:16.881+0800: 27255.691: [GC remark 2022-11-23T15:33:16.881+0800: 27255.691: [Finalize Marking, 0.0001521 secs] 2022-11-23T15:33:16.882+0800: 27255.692: [GC ref-proc, 0.0006298 secs] 2022-11-23T15:33:16.882+0800: 27255.692: [Unloading, 0.0118105 secs], 0.0180534 secs]
 [Times: user=0.04 sys=0.00, real=0.02 secs] 
2022-11-23T15:33:16.900+0800: 27255.710: [GC cleanup 925M->925M(1024M), 0.0041387 secs]
 [Times: user=0.01 sys=0.00, real=0.00 secs] 
2022-11-23T15:34:15.075+0800: 27313.885: [GC pause (young) 27313.885: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 2602, predicted base time: 3.19 ms, remaining time: 96.81 ms, target pause time: 100.00 ms]
 27313.885: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 45 regions, survivors: 6 regions, predicted young region time: 7.09 ms]
 27313.885: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 45 regions, survivors: 6 regions, old: 0 regions, predicted pause time: 10.28 ms, target pause time: 100.00 ms]
 27313.895: [G1Ergonomics (Concurrent Cycles) do not request concurrent cycle initiation, reason: still doing mixed collections, occupancy: 941621248 bytes, allocation request: 0 bytes, threshold: 483183810 bytes (45.00 %), source: end of GC]
 27313.895: [G1Ergonomics (Mixed GCs) do not start mixed GCs, reason: reclaimable percentage not over threshold, candidate old regions: 8 regions, reclaimable: 2873312 bytes (0.27 %), threshold: 5.00 %]
, 0.0100596 secs]
   [Parallel Time: 8.9 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 27313885.0, Avg: 27313887.0, Max: 27313888.9, Diff: 4.0]
      [Ext Root Scanning (ms): Min: 0.0, Avg: 0.6, Max: 1.2, Diff: 1.2, Sum: 2.2]
      [Update RS (ms): Min: 0.0, Avg: 1.3, Max: 2.6, Diff: 2.6, Sum: 5.2]
         [Processed Buffers: Min: 0, Avg: 3.5, Max: 10, Diff: 10, Sum: 14]
      [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: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 4.9, Avg: 5.0, Max: 5.1, Diff: 0.2, Sum: 20.1]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
         [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 4.9, Avg: 6.9, Max: 8.9, Diff: 4.0, Sum: 27.6]
      [GC Worker End (ms): Min: 27313893.9, Avg: 27313893.9, Max: 27313893.9, Diff: 0.0]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.1 ms]
   [Other: 1.0 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.7 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.1 ms]
   [Eden: 45.0M(45.0M)->0.0B(46.0M) Survivors: 6144.0K->5120.0K Heap: 944.1M(1024.0M)->899.8M(1024.0M)]
 [Times: user=0.03 sys=0.00, real=0.01 secs] 
2022-11-23T15:34:15.631+0800: 27314.441: [GC pause (young) 27314.441: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 4127, predicted base time: 4.55 ms, remaining time: 95.45 ms, target pause time: 100.00 ms]
 27314.441: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 46 regions, survivors: 5 regions, predicted young region time: 6.81 ms]
 27314.441: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 46 regions, survivors: 5 regions, old: 0 regions, predicted pause time: 11.36 ms, target pause time: 100.00 ms]
 27314.450: [G1Ergonomics (Concurrent Cycles) request concurrent cycle initiation, reason: occupancy higher than threshold, occupancy: 942669824 bytes, allocation request: 0 bytes, threshold: 483183810 bytes (45.00 %), source: end of GC]
, 0.0093238 secs]
   [Parallel Time: 8.6 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 27314441.0, Avg: 27314441.0, Max: 27314441.0, Diff: 0.0]
      [Ext Root Scanning (ms): Min: 0.6, Avg: 0.7, Max: 0.7, Diff: 0.1, Sum: 2.7]
      [Update RS (ms): Min: 2.3, Avg: 2.5, Max: 2.7, Diff: 0.4, Sum: 9.9]
         [Processed Buffers: Min: 3, Avg: 5.2, Max: 9, Diff: 6, Sum: 21]
      [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: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 5.1, Avg: 5.3, Max: 5.5, Diff: 0.4, Sum: 21.4]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
         [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 8.5, Avg: 8.5, Max: 8.5, Diff: 0.0, Sum: 34.1]
      [GC Worker End (ms): Min: 27314449.5, Avg: 27314449.5, Max: 27314449.5, Diff: 0.0]
   [Code Root Fixup: 0.1 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.0 ms]
   [Other: 0.7 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.3 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.1 ms]
   [Eden: 46.0M(46.0M)->0.0B(44.0M) Survivors: 5120.0K->7168.0K Heap: 945.8M(1024.0M)->903.2M(1024.0M)]
 [Times: user=0.03 sys=0.00, real=0.01 secs] 
 27374.524: [G1Ergonomics (Concurrent Cycles) request concurrent cycle initiation, reason: occupancy higher than threshold, occupancy: 942669824 bytes, allocation request: 589840 bytes, threshold: 483183810 bytes (45.00 %), source: concurrent humongous allocation]
 27374.525: [G1Ergonomics (Concurrent Cycles) request concurrent cycle initiation, reason: requested by GC cause, GC cause: G1 Humongous Allocation]
 27374.525: [G1Ergonomics (Concurrent Cycles) initiate concurrent cycle, reason: concurrent cycle initiation requested]
2022-11-23T15:35:15.715+0800: 27374.525: [GC pause (young) (initial-mark) 27374.525: [G1Ergonomics (CSet Construction) start choosing CSet, _pending_cards: 1557, predicted base time: 3.33 ms, remaining time: 96.67 ms, target pause time: 100.00 ms]
 27374.525: [G1Ergonomics (CSet Construction) add young regions to CSet, eden: 12 regions, survivors: 7 regions, predicted young region time: 4.48 ms]
 27374.525: [G1Ergonomics (CSet Construction) finish choosing CSet, eden: 12 regions, survivors: 7 regions, old: 0 regions, predicted pause time: 7.81 ms, target pause time: 100.00 ms]
, 0.0065173 secs]
   [Parallel Time: 5.7 ms, GC Workers: 4]
      [GC Worker Start (ms): Min: 27374524.8, Avg: 27374524.8, Max: 27374524.8, Diff: 0.0]
      [Ext Root Scanning (ms): Min: 0.7, Avg: 0.8, Max: 0.8, Diff: 0.1, Sum: 3.0]
      [Update RS (ms): Min: 0.5, Avg: 0.6, Max: 0.9, Diff: 0.4, Sum: 2.5]
         [Processed Buffers: Min: 1, Avg: 2.2, Max: 5, Diff: 4, Sum: 9]
      [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: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
      [Object Copy (ms): Min: 4.0, Avg: 4.2, Max: 4.3, Diff: 0.4, Sum: 16.9]
      [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
         [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 4]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
      [GC Worker Total (ms): Min: 5.6, Avg: 5.6, Max: 5.7, Diff: 0.0, Sum: 22.6]
      [GC Worker End (ms): Min: 27374530.4, Avg: 27374530.4, Max: 27374530.4, Diff: 0.0]
   [Code Root Fixup: 0.0 ms]
   [Code Root Purge: 0.0 ms]
   [Clear CT: 0.0 ms]
   [Other: 0.7 ms]
      [Choose CSet: 0.0 ms]
      [Ref Proc: 0.4 ms]
      [Ref Enq: 0.0 ms]
      [Redirty Cards: 0.0 ms]
      [Humongous Register: 0.0 ms]
      [Humongous Reclaim: 0.0 ms]
      [Free CSet: 0.0 ms]
   [Eden: 12.0M(44.0M)->0.0B(49.0M) Survivors: 7168.0K->2048.0K Heap: 915.2M(1024.0M)->901.1M(1024.0M)]
 [Times: user=0.02 sys=0.00, real=0.00 secs]

我使用 GCView 打开 GC日志，可以看到随着堆使用的越来越高，Full GC 频繁触发