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
目前創(chuàng)新互聯(lián)已為上千多家的企業(yè)提供了網(wǎng)站建設(shè)、域名、雅安服務(wù)器托管、成都網(wǎng)站托管、企業(yè)網(wǎng)站設(shè)計、商城網(wǎng)站維護(hù)等服務(wù)，公司將堅持客戶導(dǎo)向、應(yīng)用為本的策略，正道將秉承"和諧、參與、激情"的文化，與客戶和合作伙伴齊心協(xié)力一起成長，共同發(fā)展。
重慶分公司
重慶分公司
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 $HBASE_OPTS"可以查詢到log的相關(guān)信息
#jstat -gccause 79751 1000 1000 //獲取GC相關(guān)指標(biāo)，表示每1000毫秒查詢一次79751垃圾收集狀況。
Usage: jstat -help|-options
?????? jstat -
S0 S1 E O P YGC YGCT FGC FGCT GCT LGCC GCC
0.00 8.98 11.16 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 12.79 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 14.94 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 16.04 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 17.98 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 20.34 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 21.83 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
0.00 8.98 22.64 69.83 12.33 156 50.788 16 280.103 330.891 unknown GCCause No GC
E列代表
O E-->O 新生代轉(zhuǎn)移到老代，Ｏ積累到80%就會觸發(fā)full gc
具體意思如下：
E（表示，Eden），代表這臺服務(wù)器的新生代Eden區(qū)使用了11.16的空間，
S0 S1 兩個Survivor區(qū)(S0,S1表示Survivor0、Survivor1),Survivor0里面是空的，Survivor1占了8.98%
老年代（O，表示old) 和永久帶（P，表示Permanent）分別使用了69.83% 和12.33%的空間。
程序運行以來共發(fā)生Minor GC(YGC ,表示young gc)156次，總耗時50.788秒；
發(fā)生Fulle GC （FGC，表示full GC ）16次，full GC總耗時（FGCT，表示full gc time）為330.891秒，總的GC總耗時（GCT，表示GC Time）為330.891秒
LGCC Cause of last Garbage Collection.
GCC Cause of current Garbage Collection.
Java 6 JDK輸出如下：
[hadoop@0321 logs]$ 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[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
關(guān)于最大gc停頓時間
在做minor gc和mixed gc時，收集器會在內(nèi)存中維系一個remembered set，這個set包含了heap中所有對象的引用，用以確定哪些可以被回收。
每次gc時，g1會通過一個預(yù)測模型來計算每個region進(jìn)行回收的時間，從而從中選出停頓時間在MaxGCPauseMillis之內(nèi)的region進(jìn)行垃圾回收
?
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，因為old區(qū)比較大，導(dǎo)致GC時間比較長，并且在GC期間java進(jìn)程停止對外相應(yīng)，并且自身也不對外響應(yīng)，導(dǎo)致regionserver無法向zookeeper注冊心跳信息，超過zookeeper （
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) =================== 測試數(shù)據(jù)ConcGCThreads 不能大于-XX:ParallelGCThreads，否則會報錯
-XX:InitiatingHeapOccupancyPercent=60? 堆占用了多少的時候就觸發(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
[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
