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javaGC筆記-創(chuàng)新互聯(lián)

以hbase為例：在hbase的配置文件路徑下，設(shè)置了GC log輸出路徑/app/hbase-config/hbase-env.sh

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export HBASE_OPTS="-Xmx16384m -Xms16384m -Xmn8192m -XX:PermSize=160M -XX:MaxPermSize=160M -XX:+UseConcMarkSweepGC -XX:+UseParNewGC  -XX:CMSInitiatingOccupancyFraction=70 -XX:+UseCMSCompactAtFullCollection -XX:CMSFullGCsBeforeCompaction=3  -XX:+CMSParallelRemarkEnabled -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:PrintFLSStatistics=1 -Xloggc:/app/hbase/logs/hbase_gc.log $HBASE_OPTS"

可以查詢(xún)到log的相關(guān)信息

#jstat -gccause 79751 1000 1000 //獲取GC相關(guān)指標(biāo)，表示每1000毫秒查詢(xún)一次79751垃圾收集狀況。
Usage: jstat -help|-options
?????? jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
?參數(shù)解釋?zhuān)?br/>Options — 選項(xiàng)，我們一般使用 -gcutil 查看gc情況
vmid??? — VM的進(jìn)程號(hào)，即當(dāng)前運(yùn)行的java進(jìn)程號(hào)
interval– 間隔時(shí)間，單位為秒或者毫秒
count?? — 打印次數(shù)，如果缺省則打印無(wú)數(shù)次

S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC
  0.00   8.98  11.16  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  12.79  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  14.94  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  16.04  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  17.98  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  20.34  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  21.83  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC
  0.00   8.98  22.64  69.83  12.33    156   50.788    16  280.103  330.891 unknown GCCause      No GC

E列代表
O E-->O 新生代轉(zhuǎn)移到老代，Ｏ積累到80%就會(huì)觸發(fā)full gc

具體意思如下：
E（表示，Eden），代表這臺(tái)服務(wù)器的新生代Eden區(qū)使用了11.16的空間，
S0 S1 兩個(gè)Survivor區(qū)(S0,S1表示Survivor0、Survivor1),Survivor0里面是空的，Survivor1占了8.98%

老年代（O，表示old) 和永久帶（P，表示Permanent）分別使用了69.83% 和12.33%的空間。
程序運(yùn)行以來(lái)共發(fā)生Minor GC(YGC ,表示young gc)156次，總耗時(shí)50.788秒；
發(fā)生Fulle GC （FGC，表示full GC ）16次，full GC總耗時(shí)（FGCT，表示full gc time）為330.891秒，總的GC總耗時(shí)（GCT，表示GC Time）為330.891秒
LGCC Cause of last Garbage Collection.
GCC Cause of current Garbage Collection.

Java 6 JDK輸出如下：
[hadoop@0321 logs]$ jmap -heap 29877

Attaching to process ID 29877, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 20.45-b01

using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 21474836480 (20480.0MB)
   NewSize          = 4294967296 (4096.0MB)
   MaxNewSize       = 4294967296 (4096.0MB)
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 67108864 (64.0MB)
   MaxPermSize      = 67108864 (64.0MB)

Heap Usage:
New Generation (Eden + 1 Survivor Space):
   capacity = 3865509888 (3686.4375MB)
   used     = 481048576 (458.763671875MB)
   free     = 3384461312 (3227.673828125MB)
   12.444634470949257% used
Eden Space:
   capacity = 3436052480 (3276.875MB)
   used     = 481048576 (458.763671875MB)
   free     = 2955003904 (2818.111328125MB)
   14.00003576196834% used
From Space:
   capacity = 429457408 (409.5625MB)
   used     = 0 (0.0MB)
   free     = 429457408 (409.5625MB)
   0.0% used
To Space:
   capacity = 429457408 (409.5625MB)
   used     = 0 (0.0MB)
   free     = 429457408 (409.5625MB)
   0.0% used
concurrent mark-sweep generation:
   capacity = 12884901888 (12288.0MB)
   used     = 0 (0.0MB)
   free     = 12884901888 (12288.0MB)
   0.0% used
Perm Generation:
   capacity = 67108864 (64.0MB)
   used     = 21153816 (20.173851013183594MB)
   free     = 45955048 (43.826148986816406MB)
   31.521642208099365% used
  • Eden from to 3個(gè)加起來(lái)為Young 區(qū)

[hbase@0321 ~]$ jps
10424 Jps
8229 HRegionServer

[hbase@0321 ~]$ jmap -heap 8229
Attaching to process ID 8229, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.71-b01

using thread-local object allocation.
Garbage-First (G1) GC with 6 thread(s)

Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 25769803776 (24576.0MB)
NewSize = 1363144 (1.2999954223632812MB)
MaxNewSize = 17592186044415 MB
OldSize = 5452592 (5.1999969482421875MB)
NewRatio = 2
SurvivorRatio = 8
PermSize = 16777216 (16.0MB)
MaxPermSize = 83886080 (80.0MB)
G1HeapRegionSize = 8388608 (8.0MB)

Heap Usage:
G1 Heap:
regions = 3072
capacity = 25769803776 (24576.0MB)
used = 20409483264 (19464.0MB)
free = 5360320512 (5112.0MB)
79.19921875% used
G1 Young Generation:
Eden Space:
regions = 89
capacity = 1182793728 (1128.0MB)
used = 746586112 (712.0MB)
free = 436207616 (416.0MB)
63.12056737588652% used
Survivor Space:
regions = 20
capacity = 167772160 (160.0MB)
used = 167772160 (160.0MB)
free = 0 (0.0MB)
100.0% used
G1 Old Generation:
regions = 2324
capacity = 24419237888 (23288.0MB)
used = 19495124992 (18592.0MB)
free = 4924112896 (4696.0MB)
79.83510821023704% used
Perm Generation:
capacity = 50331648 (48.0MB)
used = 42303832 (40.344078063964844MB)
free = 8027816 (7.655921936035156MB)
84.05016263326009% used

G1 GC筆記：

關(guān)于大gc停頓時(shí)間
在做minor gc和mixed gc時(shí)，收集器會(huì)在內(nèi)存中維系一個(gè)remembered set，這個(gè)set包含了heap中所有對(duì)象的引用，用以確定哪些可以被回收。
每次gc時(shí)，g1會(huì)通過(guò)一個(gè)預(yù)測(cè)模型來(lái)計(jì)算每個(gè)region進(jìn)行回收的時(shí)間，從而從中選出停頓時(shí)間在MaxGCPauseMillis之內(nèi)的region進(jìn)行垃圾回收
?

關(guān)于mixed gc

mixed gc是一種既回收young區(qū)，也回收old區(qū)的垃圾回收方式，它觸發(fā)的條件是-XX:InitiatingHeapOccupancyPercent，mixed gc的目的就是為了延遲full gc的產(chǎn)生

同理YGC指的是回收young的垃圾回收方式

Full GC 指的是回收Old去的垃圾回收方式，因?yàn)閛ld區(qū)比較大，導(dǎo)致GC時(shí)間比較長(zhǎng)，并且在GC期間java進(jìn)程停止對(duì)外相應(yīng)，并且自身也不對(duì)外響應(yīng)，導(dǎo)致regionserver無(wú)法向zookeeper注冊(cè)心跳信息，超過(guò)zookeeper （ <name>zookeeper.session.timeout</name>） session時(shí)間，就會(huì)被zookeeper置為dead。

Hbase G1參數(shù)調(diào)整：

待修改的參數(shù)，修改GC的參數(shù)需要重啟集群，安排在下次重啟。

-XX:ConcGCThreads=12并發(fā)標(biāo)記的執(zhí)行線程數(shù) =================== 測(cè)試數(shù)據(jù)ConcGCThreads 不能大于-XX:ParallelGCThreads，否則會(huì)報(bào)錯(cuò)
-XX:InitiatingHeapOccupancyPercent=60? 堆占用了多少的時(shí)候就觸發(fā)GC，默認(rèn)為45
-XX:ParallelGCThreads=12 30

[hbase@0321 ~]$ jstat -gccapacity 61540
NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC PGCMN PGCMX PGC PC YGC FGC
0.0 52428800.0 2490368.0 0.0 294912.0 2195456.0 0.0 52428800.0 44695552.0 44695552.0 16384.0 81920.0 49152.0 49152.0 2 0

GC 常見(jiàn)命令：

[hbase@ 0321 ~]$ jmap -heap 61540

Attaching to process ID 61540, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.71-b01

using thread-local object allocation.
Garbage-First (G1) GC with 30 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 53687091200 (51200.0MB)
   NewSize          = 1363144 (1.2999954223632812MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5452592 (5.1999969482421875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 16777216 (16.0MB)
   MaxPermSize      = 83886080 (80.0MB)
   G1HeapRegionSize = 16777216 (16.0MB)

Heap Usage:
G1 Heap:
   regions  = 2880
   capacity = 48318382080 (46080.0MB)
   used     = 2519304864 (2402.5963439941406MB)
   free     = 45799077216 (43677.40365600586MB)
   5.213967760403951% used
G1 Young Generation:
Eden Space:
   regions  = 7
   capacity = 2248146944 (2144.0MB)
   used     = 117440512 (112.0MB)
   free     = 2130706432 (2032.0MB)
   5.223880597014926% used
Survivor Space:
   regions  = 18
   capacity = 301989888 (288.0MB)
   used     = 301989888 (288.0MB)
   free     = 0 (0.0MB)
   100.0% used
G1 Old Generation:
   regions  = 126
   capacity = 45768245248 (43648.0MB)
   used     = 2099874464 (2002.5963439941406MB)
   free     = 43668370784 (41645.40365600586MB)
   4.588059805705051% used
Perm Generation:
   capacity = 50331648 (48.0MB)
   used     = 42610464 (40.636505126953125MB)
   free     = 7721184 (7.363494873046875MB)
   84.65938568115234% used

13018 interned Strings occupying 1388240 bytes.

[hbase@0321 ~]$ jstat -gccause -h 10 61540 1000 1000

  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC
  0.00 100.00  92.54  20.26  85.06     16    1.794     0    0.000    1.794 G1 Evacuation Pause  No GC
  0.00 100.00  92.54  20.26  85.06     16    1.794     0    0.000    1.794 G1 Evacuation Pause  No GC
  0.00 100.00  92.54  20.26  85.06     16    1.794     0    0.000    1.794 G1 Evacuation Pause  No GC
  0.00 100.00  93.28  20.26  85.06     16    1.794     0    0.000    1.794 G1 Evacuation Pause  No GC
  0.00 100.00  93.28  20.26  85.06     16    1.794     0    0.000    1.794 G1 Evacuation Pause  No GC
  0.00 100.00  93.28  20.26  85.06     16    1.794     0    0.000    1.794 G1 Evacuation Pause  No GC
  0.00 100.00   1.42  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   1.42  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   3.55  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  S0     S1     E      O      P     YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC
  0.00 100.00   4.26  21.24  85.06     17    1.877     0    0.000    1.877 G1 Evacuation Pause  No GC

#jstat -gcutil 27912 1s 50

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