内容简介：Lists the instrumented Java Virtual Machines (JVMs) on the target system.如果Java进程关闭了默认开启的UsePerfData参数（Monitors Java Virtual Machine (JVM) statistics.
Lists the instrumented Java Virtual Machines (JVMs) on the target system.
如果 Java 进程关闭了默认开启的UsePerfData参数（ -XX:-UsePerfData ），那么 jps/jstat 将 无法探知 到该Java进程
$ jps 1408 Jps 19 LiveCoverMain
| 参数 | 备注 |
|---|---|
| m | Displays the arguments passed to the main method . The output may be null for embedded JVMs. |
| l | Displays the full package name for the application’s main class or the full path name to the application’s JAR file. |
| v | Displays the arguments passed to the JVM . |
jstat
Monitors Java Virtual Machine (JVM) statistics.
➜ ~ jstat -options -class -compiler -gc -gccapacity -gccause -gcmetacapacity -gcnew -gcnewcapacity -gcold -gcoldcapacity -gcutil -printcompilation
class
Displays statistics about the behavior of the class loader .
$ jstat -class 19 Loaded Bytes Unloaded Bytes Time 15375 27526.8 54 74.3 68.95
| 参数 | 备注 |
|---|---|
| Loaded | Number of classes loaded. |
| Bytes | Number of kBs loaded. |
| Unloaded | Number of classes unloaded. |
| Bytes | Number of Kbytes unloaded. |
| Time | Time spent performing class loading and unloading operations. |
compiler
Displays statistics about the behavior of the Java HotSpot VM Just-in-Time compiler.
$ jstat -compiler 19 Compiled Failed Invalid Time FailedType FailedMethod 17421 1 0 122.19 1 org/apache/skywalking/apm/dependencies/net/bytebuddy/pool/TypePool$Default$WithLazyResolution doResolve
| 参数 | 备注 |
|---|---|
| Compiled | Number of compilation tasks performed. |
| Failed | Number of compilations tasks failed. |
| Invalid | Number of compilation tasks that were invalidated. |
| Time | Time spent performing compilation tasks. |
| FailedType | Compile type of the last failed compilation. |
| FailedMethod | Class name and method of the last failed compilation. |
printcompilation
Displays Java HotSpot VM compilation method statistics.
$ jstat -printcompilation 19 Compiled Size Type Method 17423 204 1 io/netty/util/internal/MpscLinkedQueue offer
| 参数 | 备注 |
|---|---|
| Compiled | Number of compilation tasks performed by the most recently compiled method. |
| Size | Number of bytes of byte code of the most recently compiled method. |
| Type | Compilation type of the most recently compiled method. |
| Method | Class name and method name identifying the most recently compiled method. |
gc
Displays statistics about the behavior of the garbage collected heap.
jstat -gc 19 S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT 43648.0 43648.0 0.0 356.5 43776.0 17636.4 1835008.0 407774.3 91668.0 82097.8 12108.0 10130.4 33313 553.212 6 0.128 553.340
| 参数 | 备注 |
|---|---|
| S0C | Current survivor space 0 capacity (kB). |
| S1C | Current survivor space 1 capacity (kB). |
| S0U | Survivor space 0 utilization (kB). |
| S1U | Survivor space 1 utilization (kB). |
| EC | Current eden space capacity (kB). |
| EU | Eden space utilization (kB). |
| OC | Current old space capacity (kB). |
| OU | Old space utilization (kB). |
| MC |
1. Metaspace capacity (kB). 2. Klass Metaspace以及NoKlass Metaspace两者总共 committed 的内存大小 |
| MU |
1. Metacspace utilization (kB). 2. Klass Metaspace以及NoKlass Metaspace两者已经使用了的内存大小 |
| CCSC |
1. Compressed class space capacity (kB). 2. Klass Metaspace的已经committed的内存大小 |
| CCSU |
1. Compressed class space used (kB). 2. Klass Metaspace的已经被使用的内存大小 |
| YGC | Number of young generation garbage collection events. |
| YGCT | Young generation garbage collection time. |
| FGC | Number of full GC events. |
| FGCT | Full garbage collection time. |
| GCT | Total garbage collection time. |
Metaspace相关内容可参考： JVM源码分析之Metaspace解密
G1
$ jstat -gc -t 13903
Timestamp S0C S1C S0U S1U EC EU OC OU PC PU YGC YGCT FGC FGCT GCT
554652.2 0.0 8192.0 0.0 8192.0 5275648.0 4276224.0 3104768.0 755520.9 131072.0 61178.3 8219 169.021 0 0.000 169.021
- S0C和S0U始终为0，这是因为使用G1 GC时，JVM不再设置Eden区、Survivor区和Old区的 内存边界 ，而是将堆划分为若干个 等长 内存区域
- 每个内存区域都可以作为Eden区、Survivor区和Old区，并且可以在不同区域类型之间来回切换
- 因此， 逻辑上只有一个Survivor区 ，当需要迁移Survivor区中的数据（Copying），只需要申请一个或多个内存区域，作为新的Survivor区
-
当发生垃圾回收时，JVM可能出现Survivor内存区域内的对象 全被回收
或者 全被晋升
的现象
- 此时，JVM会将这块内存区域回收，并标记为 可分配
- 结果堆中可能 完全没有Survivor内存区域 ，S1C和S1U均为0
- 554652s = 6.4day
gcnew
Displays statistics of the behavior of the new generation .
$ jstat -gcnew 19 S0C S1C S0U S1U TT MTT DSS EC EU YGC YGCT 43648.0 43648.0 315.7 0.0 15 15 21824.0 43776.0 16609.9 34072 566.323
| 参数 | 备注 | 样例 |
|---|---|---|
| S0C | Current survivor space 0 capacity (kB). | |
| S1C | Current survivor space 1 capacity (kB). | |
| S0U | Survivor space 0 utilization (kB). | |
| S1U | Survivor space 1 utilization (kB). | |
| TT | Tenuring threshold . | 15 |
| MTT | Maximum tenuring threshold . | 15 |
| DSS | Desired survivor size (kB). |
1. -XX:TargetSurvivorRatio=50 2. Desired percentage of survivor space used after scavenge. 3. 21824KB == 0.5 * S0C |
| EC | Current eden space capacity (kB). | |
| EU | Eden space utilization (kB). | |
| YGC | Number of young generation GC events. | |
| YGCT | Young generation garbage collection time. |
gcold
Displays statistics about the behavior of the old generation and metaspace statistics.
$ jstat -gcold 19 MC MU CCSC CCSU OC OU YGC FGC FGCT GCT 92564.0 82773.0 12236.0 10223.6 1835008.0 423476.6 34693 6 0.128 575.369
| 参数 | 备注 |
|---|---|
| MC | Metaspace capacity (kB). |
| MU | Metaspace utilization (kB). |
| CCSC | Compressed class space capacity (kB). |
| CCSU | Compressed class space used (kB). |
| OC | Current old space capacity (kB). |
| OU | Old space utilization (kB). |
| YGC | Number of young generation GC events. |
| FGC | Number of full GC events. |
| FGCT | Full garbage collection time. |
| GCT | Total garbage collection time. |
gccapacity
Displays statistics about the capacities of the generations and their corresponding spaces.
$ jstat -gccapacity 19 NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC MCMN MCMX MC CCSMN CCSMX CCSC YGC FGC 131072.0 131072.0 131072.0 43648.0 43648.0 43776.0 1835008.0 1835008.0 1835008.0 1835008.0 0.0 1128448.0 91668.0 0.0 1048576.0 12108.0 33477 6
| 参数 | 备注 | 样例 |
|---|---|---|
| NGCMN | Minimum new generation capacity (kB). | |
| NGCMX | Maximum new generation capacity (kB). | |
| NGC | Current new generation capacity (kB). | |
| S0C | Current survivor space 0 capacity (kB). | |
| S1C | Current survivor space 1 capacity (kB). | |
| EC | Current eden space capacity (kB). | |
| OGCMN | Minimum old generation capacity (kB). | |
| OGCMX | Maximum old generation capacity (kB). | |
| OGC | Current old generation capacity (kB). | |
| OC | Current old space capacity (kB). | |
| MCMN | Minimum metaspace capacity (kB). | 0 |
| MCMX | Maximum metaspace capacity (kB). |
1. Klass Metaspace以及NoKlass Metaspace两者总共的 reserved
的内存大小 2. 默认情况下Klass Metaspace是通过 CompressedClassSpaceSize 这个参数来reserved 1G的内存 3. NoKlass Metaspace默认reserved的内存大小是 2*InitialBootClassLoaderMetaspaceSize 4. 1128448KB == 1.076GB |
| MC | Metaspace capacity (kB). |
1. Klass Metaspace以及NoKlass Metaspace两者总共 committed
的内存大小 2. 91668KB == 89.5MB |
| CCSMN | Compressed class space minimum capacity (kB). | 0 |
| CCSMX | Compressed class space maximum capacity (kB). |
1. Klass Metaspace reserved的内存大小 2. 1048576KB == 1GB |
| CCSC | Compressed class space capacity (kB). |
1. Klass Metaspace的已committed的内存大小 2. 12108KB == 11.8MB |
| YGC | Number of young generation GC events. | |
| FGC | Number of full GC events. |
gcnewcapacity
Displays statistics about the sizes of the new generations and its corresponding spaces.
$ jstat -gcnewcapacity 19 NGCMN NGCMX NGC S0CMX S0C S1CMX S1C ECMX EC YGC FGC 131072.0 131072.0 131072.0 43648.0 43648.0 43648.0 43648.0 43776.0 43776.0 34383 6
| 参数 | 备注 |
|---|---|
| NGCMN | Minimum new generation capacity (kB). |
| NGCMX | Maximum new generation capacity (kB). |
| NGC | Current new generation capacity (kB). |
| S0CMX | Maximum survivor space 0 capacity (kB). |
| S0C | Current survivor space 0 capacity (kB). |
| S1CMX | Maximum survivor space 1 capacity (kB). |
| S1C | Current survivor space 1 capacity (kB). |
| ECMX | Maximum eden space capacity (kB). |
| EC | Current eden space capacity (kB). |
| YGC | Number of young generation GC events. |
| FGC | Number of full GC events. |
gcoldcapacity
Displays statistics about the sizes of the old generation.
$ jstat -gcoldcapacity 19 OGCMN OGCMX OGC OC YGC FGC FGCT GCT 1835008.0 1835008.0 1835008.0 1835008.0 34478 6 0.128 572.454
| 参数 | 备注 |
|---|---|
| OGCMN | Minimum old generation capacity (kB). |
| OGCMX | Maximum old generation capacity (kB). |
| OGC | Current old generation capacity (kB). |
| OC | Current old space capacity (kB). |
| YGC | Number of young generation GC events. |
| FGC | Number of full GC events. |
| FGCT | Full garbage collection time. |
| GCT | Total garbage collection time. |
gcmetacapacity
Displays statistics about the sizes of the metaspace.
$ jstat -gcmetacapacity 19
MCMN MCMX MC CCSMN CCSMX CCSC YGC FGC FGCT GCT
0.0 1130496.0 92564.0 0.0 1048576.0 12236.0 34593 6 0.128 574.271
| 参数 | 备注 |
|---|---|
| MCMN | Minimum metaspace capacity (kB). |
| MCMX | Maximum metaspace capacity (kB). |
| MC | Metaspace capacity (kB). |
| CCSMN | Compressed class space minimum capacity (kB). |
| CCSMX | Compressed class space maximum capacity (kB). |
| YGC | Number of young generation GC events. |
| FGC | Number of full GC events. |
| FGCT | Full garbage collection time. |
| GCT | Total garbage collection time. |
gcutil
Displays a summary about garbage collection statistics.
$ jstat -gcutil 19 S0 S1 E O M CCS YGC YGCT FGC FGCT GCT 0.16 0.00 14.11 23.02 89.37 83.50 34596 574.184 6 0.128 574.312
| 参数 | 备注 | 样例 |
|---|---|---|
| S0 | Survivor space 0 utilization as a percentage of the space’s current capacity. | |
| S1 | Survivor space 1 utilization as a percentage of the space’s current capacity. | |
| E | Eden space utilization as a percentage of the space’s current capacity. | |
| O | Old space utilization as a percentage of the space’s current capacity. | |
| M | Metaspace utilization as a percentage of the space’s current capacity. |
1. Klass Metaspace以及NoKlass Metaspace两者总共的使用率 2. MC=92564.0, MU=82773.0, CCSC=12236.0, CCSU=10223.6 3. M = MU/MC = 89.4 4. 有时候M达到90%以上，不一定说明metaspace使用了很多，因为内存是慢慢commit的 |
| CCS | Compressed class space utilization as a percentage. |
1. NoKlass Metaspace的使用率 2. MC=92564.0, MU=82773.0, CCSC=12236.0, CCSU=10223.6 3. CCS = CCSU/CCSC = 83.5 |
| YGC | Number of young generation GC events. | |
| YGCT | Young generation garbage collection time. | |
| FGC | Number of full GC events. | |
| FGCT | Full garbage collection time. | |
| GCT | Total garbage collection time. |
gccause
Displays a summary about garbage collection statistics (same as -gcutil), with the cause of the last and current (when
applicable) garbage collection events.
$ jstat -gccause 19 S0 S1 E O M CCS YGC YGCT FGC FGCT GCT LGCC GCC 0.00 0.83 2.23 22.60 89.67 84.02 33919 563.393 6 0.128 563.521 Allocation Failure No GC
| 参数 | 备注 | 样例 |
|---|---|---|
| LGCC | Cause of last garbage collection | Allocation Failure |
| GCC | Cause of current garbage collection | No GC |
jmap
- Prints shared object memory maps or heap memory details for a process, core file, or remote debug server.
-
由于jmap将访问 堆中的所有对象
，为了保证次此过程不被应用线程干扰
- jmap需要借助 安全点机制 ，让所有线程停留在不改变堆中数据的状态
-
因此， jmap导出的堆快照必定是安全点位置的
，可能导致基于该堆快照的分析结果存在 偏差
- 例如编译生成的机器码中，某些对象的生命周期在两个安全点之间，那么:live选项将无法探知到这些对象
-
如果某个线程长时间无法跑到安全点，jmap将一直等待下去
- 垃圾回收器会主动将jstat所需要的摘要数据保存至 固定位置
- 因此jstat只需要直接读取即可
- jmap/jinfo/jstack/jcmd ，均依赖于JVM的 Attach API ，因此 只能监控本地Java进程
-
如果开启
-XX:+DisableAttachMechanism，那么基于 Attach API 的命令也将无法执行
clstats
Prints class loader wise statistics of Java heap. For each class loader, its name, how active it is, address, parent class loader, and the number and size of classes it has loaded are printed.
$ jmap -clstats 19 Attaching to process ID 19, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.131-b11 finding class loader instances ..done. computing per loader stat ..done. please wait.. computing liveness.liveness analysis may be inaccurate ... class_loader classes bytes parent_loader alive? type <bootstrap> 2508 4508619 null live <internal> 0x000000009388bb88 1 1473 null dead sun/reflect/DelegatingClassLoader@0x0000000100009df8 0x0000000090bcccb8 1 1472 0x0000000090024a50 dead sun/reflect/DelegatingClassLoader@0x0000000100009df8 ... total = 634 12693 20378456 N/A alive=1, dead=633 N/A
finalizerinfo
Prints information about objects that are awaiting finalization.
$ jmap -finalizerinfo 19 Attaching to process ID 19, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.131-b11 Number of objects pending for finalization: 0
heap
Prints a heap summary of the garbage collection used, the head configuration, and generation-wise heap usage. In addition, the number and size of interned Strings are printed.
$ jmap -heap 19 Attaching to process ID 19, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.131-b11 using parallel threads in the new generation. using thread-local object allocation. Concurrent Mark-Sweep GC Heap Configuration: MinHeapFreeRatio = 40 MaxHeapFreeRatio = 70 MaxHeapSize = 2013265920 (1920.0MB) NewSize = 134217728 (128.0MB) MaxNewSize = 134217728 (128.0MB) OldSize = 1879048192 (1792.0MB) NewRatio = 2 SurvivorRatio = 1 MetaspaceSize = 21807104 (20.796875MB) CompressedClassSpaceSize = 1073741824 (1024.0MB) MaxMetaspaceSize = 17592186044415 MB G1HeapRegionSize = 0 (0.0MB) Heap Usage: New Generation (Eden + 1 Survivor Space): capacity = 89522176 (85.375MB) used = 32297224 (30.80103302001953MB) free = 57224952 (54.57396697998047MB) 36.07734467937866% used Eden Space: capacity = 44826624 (42.75MB) used = 31529392 (30.068771362304688MB) free = 13297232 (12.681228637695312MB) 70.33630728024488% used From Space: capacity = 44695552 (42.625MB) used = 767832 (0.7322616577148438MB) free = 43927720 (41.892738342285156MB) 1.7179159125274928% used To Space: capacity = 44695552 (42.625MB) used = 0 (0.0MB) free = 44695552 (42.625MB) 0.0% used concurrent mark-sweep generation: capacity = 1879048192 (1792.0MB) used = 33776136 (32.21143341064453MB) free = 1845272056 (1759.7885665893555MB) 1.7975130251475744% used 21703 interned Strings occupying 2142592 bytes.
histo[:live]
Prints a histogram of the heap. For each Java class, the number of objects, memory size in bytes, and the fully qualified class names are printed. The JVM internal class names are printed with an asterisk (*) prefix. If the live suboption is specified, then only active objects are counted.
$ jmap -histo:live 19 num #instances #bytes class name ---------------------------------------------- 1: 72102 6440744 [C 2: 5996 4159456 [B 3: 19079 1783760 [Ljava.lang.Object; 4: 71213 1709112 java.lang.String ... Total 529634 28005336
dump:[live,] format=b, file=filename
Dumps the Java heap in hprof binary format to filename. The live suboption is optional, but when specified, only the active objects in the heap are dumped.
相关的JVM参数： -XX:+HeapDumpAfterFullGC
， -XX:+HeapDumpOnOutOfMemoryError
$ jmap -dump:live,format=b,file=/tmp/cover.hprof 19 Dumping heap to /tmp/cover.hprof ... Heap dump file created
jinfo
Generates configuration information
$ jinfo 19 Attaching to process ID 19, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.131-b11 Java System Properties: java.runtime.name = Java(TM) SE Runtime Environment java.vm.version = 25.131-b11 ... conf.key = lz_live_cover ... VM Flags: Non-default VM flags: -XX:CICompilerCount=2 -XX:+CMSClassUnloadingEnabled .... Command line: -Dconf.key=lz_live_cover -Dconf.env=pre
sysprops
Prints Java system properties as name-value pairs.
$ jinfo -sysprops 19 Attaching to process ID 19, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.131-b11 java.runtime.name = Java(TM) SE Runtime Environment java.vm.version = 25.131-b11 ... java.vm.vendor = Oracle Corporation conf.key = lz_live_cover ... java.vm.name = Java HotSpot(TM) 64-Bit Server VM sun.java.launcher = SUN_STANDARD ...
flags
$ jinfo -flags 19 Attaching to process ID 19, please wait... Debugger attached successfully. Server compiler detected. JVM version is 25.131-b11 Non-default VM flags: -XX:CICompilerCount=2 -XX:+CMSClassUnloadingEnabled ... Command line: -Dconf.key=lz_live_cover -Dconf.env=pre ...
manageable参数
$ java -XX:+PrintFlagsFinal -version | grep manageable
intx CMSAbortablePrecleanWaitMillis = 100 {manageable}
intx CMSTriggerInterval = -1 {manageable}
intx CMSWaitDuration = 2000 {manageable}
bool HeapDumpAfterFullGC = false {manageable}
bool HeapDumpBeforeFullGC = false {manageable}
bool HeapDumpOnOutOfMemoryError = false {manageable}
ccstr HeapDumpPath = {manageable}
uintx MaxHeapFreeRatio = 100 {manageable}
uintx MinHeapFreeRatio = 0 {manageable}
bool PrintClassHistogram = false {manageable}
bool PrintClassHistogramAfterFullGC = false {manageable}
bool PrintClassHistogramBeforeFullGC = false {manageable}
bool PrintConcurrentLocks = false {manageable}
bool PrintGC = false {manageable}
bool PrintGCDateStamps = false {manageable}
bool PrintGCDetails = false {manageable}
bool PrintGCID = false {manageable}
bool PrintGCTimeStamps = false {manageable}
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
flag
Prints the name and value of the specified command-line flag.
$ jinfo -flag HeapDumpAfterFullGC 19 -XX:-HeapDumpAfterFullGC
flag [+|-]name
Enables or disables the specified Boolean command-line flag.
$ jinfo -flag +HeapDumpAfterFullGC 19 $ jinfo -flag HeapDumpAfterFullGC 19 -XX:+HeapDumpAfterFullGC
flag name=value
Sets the specified command-line flag to the specified value.
$ jinfo -flag CMSWaitDuration=1999 19 $ jinfo -flag CMSWaitDuration 19 -XX:CMSWaitDuration=1999
jstack
Prints Java thread stack traces for a Java process, core file, or remote debug server.
jstack的一个常用应用场景为 死锁检测
$ jstack 19120 2019-01-10 09:53:21 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.181-b13 mixed mode): ... "t3" #12 prio=5 os_prio=31 tid=0x00007faa948b4800 nid=0xf07 waiting for monitor entry [0x00007000043c8000] java.lang.Thread.State: BLOCKED (on object monitor) at me.zhongmingmao.advanced.command.SyncThread.run(ThreadDeadlock.java:39) - waiting to lock <0x0000000795700530> (a java.lang.Object) - locked <0x0000000795700550> (a java.lang.Object) at java.lang.Thread.run(Thread.java:748) "t2" #11 prio=5 os_prio=31 tid=0x00007faa948b4000 nid=0x3c03 waiting for monitor entry [0x0000700005581000] java.lang.Thread.State: BLOCKED (on object monitor) at me.zhongmingmao.advanced.command.SyncThread.run(ThreadDeadlock.java:39) - waiting to lock <0x0000000795700550> (a java.lang.Object) - locked <0x0000000795700540> (a java.lang.Object) at java.lang.Thread.run(Thread.java:748) "t1" #10 prio=5 os_prio=31 tid=0x00007faa948b3000 nid=0x4203 waiting for monitor entry [0x000070000547e000] java.lang.Thread.State: BLOCKED (on object monitor) at me.zhongmingmao.advanced.command.SyncThread.run(ThreadDeadlock.java:39) - waiting to lock <0x0000000795700540> (a java.lang.Object) - locked <0x0000000795700530> (a java.lang.Object) at java.lang.Thread.run(Thread.java:748) ... Found one Java-level deadlock: ============================= "t3": waiting to lock monitor 0x00007faa94811b58 (object 0x0000000795700530, a java.lang.Object), which is held by "t1" "t1": waiting to lock monitor 0x00007faa9480da08 (object 0x0000000795700540, a java.lang.Object), which is held by "t2" "t2": waiting to lock monitor 0x00007faa94811aa8 (object 0x0000000795700550, a java.lang.Object), which is held by "t3" ... Found 1 deadlock.
jcmd
Sends diagnostic command requests to a running Java Virtual Machine (JVM).
jcmd可以替代上面除了jstat之外的所有命令，并没有保留jstat的输出格式
查看进程
$ jcmd -l 19 fm.lizhi.live.cover.LiveCoverMain lz-live-cover-pre-deployment-5f45b6955d-f4xjj 3241 sun.tools.jcmd.JCmd -l
查看性能统计
$ jcmd 19 PerfCounter.print java.ci.totalTime=445938928367 java.cls.loadedClasses=20317 ... java.threads.daemon=121 java.threads.live=124 java.threads.livePeak=125 java.threads.started=2458 ...
可执行的操作
$ jcmd 19 help 19: The following commands are available: JFR.stop JFR.start JFR.dump JFR.check VM.native_memory VM.check_commercial_features VM.unlock_commercial_features ManagementAgent.stop ManagementAgent.start_local ManagementAgent.start GC.rotate_log Thread.print GC.class_stats GC.class_histogram GC.heap_dump GC.run_finalization GC.run VM.uptime VM.flags VM.system_properties VM.command_line VM.version help
VM.uptime
$ jcmd 19 VM.uptime 19: 87089.850 s
GC.run
$ jcmd 19 GC.run 19: Command executed successfully
Thread.print
$ jcmd 3721 Thread.print Found one Java-level deadlock: ============================= "t3": waiting to lock monitor 0x00007fd53105ff58 (object 0x0000000795700530, a java.lang.Object), which is held by "t1" "t1": waiting to lock monitor 0x00007fd53105be08 (object 0x0000000795700540, a java.lang.Object), which is held by "t2" "t2": waiting to lock monitor 0x00007fd53105fea8 (object 0x0000000795700550, a java.lang.Object), which is held by "t3"
JFR
$ jcmd 3721 JFR.check 3721: Java Flight Recorder not enabled. Use VM.unlock_commercial_features to enable. $ jcmd 3721 VM.unlock_commercial_features 3721: Commercial Features now unlocked. $ jcmd 3721 JFR.check 3721: No available recordings. Use JFR.start to start a recording.
$ jcmd 3721 JFR.start name=abc,duration=120s 3721: Started recording 1. No limit (duration/maxsize/maxage) in use. Use JFR.dump name=abc,duration=120s filename=FILEPATH to copy recording data to file. $ jcmd 3721 JFR.check 3721: Recording: recording=1 name="abc,duration=120s" (running)
$ cmd 3721 JFR.dump name=abc,duration=120s filename=abc.jfr 3721: Dumped recording "abc,duration=120s", 391.4 kB written to: /Users/zhongmingmao/Documents/source_code/github/jvm_demo/abc.jfr
$ jcmd 3721 JFR.stop name=abc,duration=120s 3721: Stopped recording "abc,duration=120s".
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移动社交时代的互动搜索营销（全彩）
萧秋水、秋叶、南方锈才 / 电子工业出版社 / 2014-8-1 / 55.00元
《移动社交时代的互动搜索营销（全彩）》跳出搜索引擎的局限，告诉读者如何利用互联网找到客户的思维。《移动社交时代的互动搜索营销（全彩）》只谈如何有效利用搜索引擎（包括移动端搜索）、电商网站、新媒体,不传播所谓的一夜暴红、一夜暴富的神话。《移动社交时代的互动搜索营销（全彩）》作者利用其丰富的实战经验，结合大量国内不同行业的实际应用案例，生动地告诉读者，怎样正确地利用搜索引擎，以很小的投资获得巨大的回报......一起来看看 《移动社交时代的互动搜索营销（全彩）》 这本书的介绍吧!
