支持启动旉择 JVM q程列表;
支持观测详细的收集器GC暂停旉;
图表支持鼠标Ud详细信息昄(旉和?;
支持 Hotspot JDK 8+版本下运? 可检?Hotspot JDK 1.5 ~ 14, ?CMS, G1{收集器下检通过;
中英双语昄.
此工具仅希望能有所帮助, 但不提供M担保.
源码地址: https://github.com/beansoftapp/gcperf
原始目: https://github.com/bitcharmer/gcperf
原始介绍: https://dzone.com/articles/visualvm-gcviewer-plugin
下蝲
gcperf.nbm 中文多语a?p>gcperf_en.nbm 英文?p>Java 8(VisualVM 1.0)适用
术语单解?
参?JDK 源码: AdaptiveSizePolicy.Design.txt
zd?liveSpace = baseFootprint + oldAlive + youngAlive 闲置?freeSpace = promoSize + edenSize
重要说明: 此项目仅支持 OpenJDK ?Hotspot, 通过使用 JVMStat API 来读取内|的 HotSpot 计数? 因ؓ某些原因, 新的q行GC (-XX:+UseParNewGC) 不再提供和旧的ƈ行扫描收集器(-XX:+UseParallelGC)相同的计数器, 所以新版下只能看到 GC 暂停旉和已提升Ҏ已存zM个图?.
其它的GC法能否昄暂未试.
q行截图:
英文截图:
]]>
中文Q内Ҏ滞后Q：http://www.oracle.com/technetwork/cn/middleware/ias/downloads/wls-main-091116-zhs.html
Oracle优秀英文博客Q?/p>
]]>
q行截图:
2010-09-10 WLSMonitor 1.1 beta
本免费版本的后箋版本收费QWLS Monitor for WebLogic 9, 10, 11g ZWeb模式开发，使用Tomcatq行部v。更多信息请咨询站长?/p>
http://cid-519b3f7aa2172030.office.live.com/self.aspx/Public/WebLogic/wlstat1.1.zip
]]>
下面列出了各个厂商的输出Q可以看到IBM的帮助最详细而且是中文的Q有意思?/p>
另外JRockitq支持一?-XX参数Q其输出如下Q?/p>
Global:
UnlockDiagnosticVMOptions = false (default, writeable)
- Enable processing of flags relating to field diagnostics
UnlockInternalVMOptions = false (default)
- Enable processing of internal, unsupported flags
Class:
FailOverToOldVerifier = true (default, writeable)
- Fail over to old verifier when split verifier fails
UseVerifierClassCache = true (default)
- Try to cache java.lang.Class lookups for old verifier.
UseClassGC = true (default)
(Alias: -Xnoclassgc)
- Allow GC of Java classes
Threads:
UseThreadPriorities = false (default)
- Use native thread priorities
DeferThrSuspendLoopCount = 4000 (default, writeable)
- Number of iterations in safepoint loop until we try blocking
SafepointSpinBeforeYield = 2000 (default, writeable)
- Number of iterations in safepoint loop until we yield instead
of pause (MP only)
UseCompilerSafepoints = true (default)
- Insert safepoint polls in compiled code
DeferPollingPageLoopCount = -1 (default)
- Number of iterations in safepoint loop before arming
safepoint poll page
UseMembarForTransitions = false (default)
- Use membar to serialize thread states.
UseNativeLockProfiling = false (default)
- Profile use of internal JVM monitors
JNI:
CheckJNICalls = false (default)
- Verify all arguments to JNI calls
AbortOnFailedJNICheck = true (default)
- Used with CheckJNICalls. If true, abort the JVM upon first
JNI parameter error.
ErrorOnFailedJNICheck = false (default)
- Used with CheckJNICalls. If true, any errors will be
signalled through a java.lang.Error.
JDK:
UseNewHashFunction = false (default)
- Use HashMaps new hash function on jdks that does not do so by
default
TreeMapNodeSize = 64 (default)
- Size of entry array in each java.util.TreeMap node
MaxDirectMemorySize = 0 (default)
- Maximum total size of NIO direct-buffer allocations
UseLazyStackTraces = true (default)
- Generate stacktraces lazily for thrown Exceptions
ShowInternalMethodsInStackTrace = false (default, writeable)
- Show JVM internal code in java stacktraces.
OS:
ReduceSignalUsage = false (default)
(Alias: -Xrs)
- Reduce the use of OS signals in Java and/or the VM
MaxRecvBufferSize = 65536 (default)
- Maximum size of byte buffer sent to recv
MaxLargePageSize = 0 (default)
- Use value as maximum size for large pages (if possible).
GC:
UseLowAddressForHeap = true (default)
- Use low 4Gb address space for Java heap if possible.
UseLargePagesForHeap = false (default)
- Attempt to use large page translation for the Java heap.
ForceLargePagesForHeap = false (default)
- Force the use of large page translation for the Java heap.
CompressedRefs = false (default)
(Alias: -XXcompressedRefs)
- Use 32-bit java references on 64-bit OS - implies a heap
maximum of 4Gb (probably less)
InitialHeapSize = 0 (default)
(Alias: -Xms)
- Initial size of Java Object heap
MaxHeapSize = 0 (default)
(Alias: -Xmx)
- Maximum size of Java Object heap
GCTimeRatio = 19 (default)
- The ratio of time spent in garbage collection compared to
outside of garbage collection.
GCTimePercentage = 0.000000 (default)
- The percentage of time spent in garbage collection of total
run time.
GCTrigger = 0 (default)
(Alias: -XXgcTrigger)
- The threshold of free heap before a concurrent GC is started
ForceEarlyOC = true (default)
- Force an early OC before old space is empty to avoid
promotion failed.
ForceEarlyOCMaxPercentage = 5.000000 (default)
- Maximum percentage of heap that is allowed to have left
before doing an early OC.
ForceYCOnLargeAllocationFailed = false (default)
- Force YC on a large allocation failure.
UseNurseryEvacuation = false (default)
- Try to evacuate the nursery when a promotion failed has
occured.
DisableEvacuationToNursery = false (default)
- Disallows evacuation to move objects to where the nursery is.
SemiRefPostponedPacketSize = 492 (default)
- The number of references in a postponed semiref packet.
SemiRefPrefetchDistance = 0 (default)
- The number of reference packet indexes to prefetch, or 0 for
no prefetch.
FinalHandleParallelThreshold = -1 (default)
- The minimum number of final handles needed to process them in
parallel.
FinalHandlePacketSize = 200 (default)
- The number of handles in a final handle packet.
MaximumNurseryPercentage = 95 (default)
- Sets the maximum size of the nursery relative to the amount
of free heap after the last old collection.
AllowYCDuringOC = true (default)
- Allow young collections during old collections.
YcAlignAll = false (default)
- Align all objects (with regards to YcAlignMaxSpill) during YC
YcAlignMaxSpill = 40 (default)
- Max spill allowed when aligning objects during YC.
FullSystemGC = false (default)
(Alias: -XXfullSystemGC)
- Always run full GC (with full compaction) when System.gc() is
called
AllowSystemGC = true (default)
(Alias: -XXnoSystemGC)
- Run a GC when System.gc() is called
GcCardTableParts = 1024 (default)
- Initial number of parts of the card table array
GcBalancePrefetchDistance = 4 (default)
- Prefetch distance in a GC balance system workpacket
GcBalancePacketSize = 493 (default)
- Packet size of GC balance system workpackets
NumGenConPrecleaningIterations = 3 (default)
- Number of precleaning iterations for gencon.
AllowEmergencyParSweep = true (default)
- Allow the OC to temporarily change concurrent sweep to
parallel if needed.
TlaWasteLimit = 0 (default)
(Alias: -XXlargeObjectLimit)
- Internal. Use -XXtlaSize:wasteLimit instead.
TlaMinSize = 0 (default)
(Alias: -XXminBlockSize)
- Internal. Use -XXtlaSize:min instead.
TlaPreferredSize = 0 (default)
- Internal. Use -XXtlaSize:preferred instead.
GC::Compaction:
UseFullCompaction = false (default)
- All compactions will be full compactions. Internal. Use
-XXcompaction:full instead.
InternalCompactionPercentage = -1.000000 (default)
- The percentage of the heap to compact for internal
compaction. Internal. Use -XXcompaction:internalPercentage
instead.
ExternalCompactionPercentage = -1.000000 (default)
- The percentage of the heap to compact for external
compaction. Internal. Use -XXcompaction:externalPercentage
instead.
InitialCompactionPercentage = -1.000000 (default)
- The initial percentage of the heap to compact, for both
internal and external compaction. Internal. Use
-XXcompaction:initialPercentage instead.
UseCompaction = true (default)
- Use compaction to reduce fragmentation. Internal. Use
-XXcompaction:enable instead.
UseAbortableCompaction = false (default)
- The compactions should be possible to abort. Internal. Use
-XXcompaction:abortable instead.
NumCompactionHeapParts = 4096 (default)
(Alias: -XXheapParts)
- The number of heap parts in compaction heuristics. Internal.
Use -XXcompaction:heapParts instead.
InitialExternalReservedHeap = 4M (default)
- The initial size of the memory reserved by external
compaction. Internal. Use
-XXcompaction:initialExternalReservedHeap instead.
UseFixedExternalReservedHeap = false (default)
- The size of the memory reserved by external compaction is
fixed. Internal. Use
-XXcompaction:externalReservedHeapIsFixed instead.
MaxCompactionReferences = 0 (default)
(Alias: -XXcompactSetLimit)
- The maximum number of references to store in compaction
before skipping. Internal. Use -XXcompaction:maxReferences
instead.
MaxCompactionReferencesPerObject = 0 (default)
(Alias: -XXcompactSetLimitPerObject)
- The maximum number of references to store per object in
compaction. Internal. Use
-XXcompaction:maxReferencesPerObject instead.
InternalCompactionParts = -1 (default)
(Alias: -XXinternalCompactRatio)
- Deprecated. Use -XXcompaction:internalPercentage instead.
ExternalCompactionParts = -1 (default)
(Alias: -XXexternalCompactRatio)
- Deprecated. Use -XXcompaction:externalPercentage instead.
Object allocation:
UseAllocPrefetch = true (default)
- Use prefetch on object allocation
RedoAllocPrefetch = true (default)
- Do prefetch on object allocation from start of the allocated
object
AllocPrefetchLineLength = -1 (default)
- Line length for allocation prefetch
AllocPrefetchDistance = -1 (default)
- Distance for allocation prefetch
AllocChunkSize = -1 (default)
- Size of chunks to clear/prefetch
Javalock:
UseLockProfiling = false (default)
- Enable Java lock profiling.
ThinLockContendedSpinCount = -1 (default)
- Number of spins between each poll when acquiring a thin lock
ThinLockContendedPollCount = -1 (default)
- Number of polls between each short nap when acquiring a thin
lock
ThinLockConvertToFatThreshold = -1 (default)
- Number of of short naps before converting thin lock to fat
FatLockContendedSpinCount = -1 (default)
- Number of spins between each poll when acquiring a fat lock
FatLockContendedPollCount = -1 (default)
- Number of polls between each short nap when acquiring a fat
lock
MonitorContendedSpinCount = -1 (default)
- Number of spins between each poll when acquiring a monitor
lock
MonitorContendedPollCount = -1 (default)
- Number of polls between each short nap when acquiring a
monitor lock
UseFatLockDeflation = true (default)
- Try to deflate fat locks to thin
FatLockDeflationThreshold = 50 (default)
- Number of uncontended entries on lock before deflation occurs
UseLockQueueLength = true (default)
- Make threads go to sleep if contention exceeds # cpus
UseFatSpin = true (default)
(Alias: -XXdisableFatSpin)
- Should we spin-try then acquiring a fat lock
UseAdaptiveFatSpin = false (default)
- Should we use adaptive spinning acquiring a fat lock
UseThreadContentionMonitoring = true (default)
- Allow thread contention monitoring
JavaLock::LazyUnlocking:
UseLazyUnlocking = true (default)
(Alias: -XXlazyUnlocking)
- Enable lazy unlocking
UseLazyUnlockingInJIT = true (default)
- Use lazy locks in JIT code
UseLazyUnlockingClassBan = true (default)
- Use class banning
UseLazyUnlockingTransferClassBan = true (default)
- Use transfer class banning
JFR:
FlightRecorder = true (default)
- Enable flightrecorder
FlightRecorderOptions = (null) (default)
- Flight recorder arguments
StartFlightRecording = (null) (default)
- Start a Flight recording with args. Equivalent to using
"start_flightrecording".
Code memory:
CodeBlockAbsorbtionSize = 16 (default)
- Maximum extra size allowed for fitting code memory chunks
FreeEmptyCodeBlocks = true (default)
- Free unused code memory
UseLargePagesForCode = false (default)
- Attempt to use large page translation compiled code.
MaxCodeMemory = 0 (default)
- Maximum amount of memory used for generated code
ReserveCodeMemory = false (default)
- Reserve all memory for code at startup
UseCodeGC = true (default)
- Allow GC of discarded compiled code
CodeGCThreshold = 0 (default)
- Released byte threshold for initiating a code GC
CodeGCReclaimThreshold = 0 (default)
- Released byte threshold before compiler attempts to reclaim
unused code space
CodeGCUseReclaim = true (default)
- Should Code GC attempt reclamation of unused code memory
Compiler broker:
MaxOptQueueLength = 0 (default)
- Maximum allowed optimization queue length before JIT thread
helps generate code
OptThreads = 1 (default)
- Number of background optimization threads
JITThreads = 1 (default)
- Number of background JIT threads
JITThreadPrio = 5 (default)
- Priority of background JIT threads
OptThreadPrio = 5 (default)
- Priority of background optimization threads
DisableOptsAfter = -1 (default)
(Alias: -Xnoopt)
- Disable optimizations after n seconds
Compiler:
PreOpt = false (default)
- Optimize all code on jit (first generation)
UseCallProfiling = false (default)
- Use call profiling on unoptimized code
StrictFP = false (default)
(Alias: -Xstrictfp)
- Force strict FP for all methods
CheckStacks = false (default)
(Alias: -Xcheckedstacks)
- Do explicit checks for stack overflow
DevirtualizeAlways = false (default)
- Forces devirtualization in jitted code
UseStringCache = false (default)
- Cache common arrays used in String constructor
MethodCodeAlignment = 32 (default)
- Byte alignment for start of method code
UseInlineObjectAlloc = true (default)
- Generate inlined object allocation code.
UseOldLockMatching = false (default)
- Compatibility mode lock matching
JVMTI:
JavaDebug = false (default)
(Alias: -Xdebug)
- Enable java debugging
Management:
DisableAttachMechanism = false (default)
- Disable mechanism that allows tools to attach to this VM
CrashOnOutOfMemoryError = false (default, writeable)
- Crash JVM process on OutOfMemory
ExitOnOutOfMemoryError = false (default, writeable)
- Terminate JVM process on OutOfMemory
ExitOnOutOfMemoryErrorExitCode = 51 (default, writeable)
- Exit code for termination of JVM process on OutOfMemory
HeapDiagnosticsOnOutOfMemoryError = false (default, writeable)
- Print Java heap diagnostics on OutOfMemory
HeapDiagnosticsPath = (null) (default, writeable)
- When HeapDiagnosticsOnOutOfMemoryError is on, the path
(filename or directory) of the dump file (defaults to
jrockit_<pid>.oomdiag in the working directory)
HeapDumpOnOutOfMemoryError = false (default, writeable)
- Dump Java heap to a hprof binary format file on OutOfMemory
HeapDumpOnCtrlBreak = false (default)
- Dump heap to file in Ctrl-Break handler
HeapDumpPath = (null) (default, writeable)
- When HeapDumpOnOutOfMemoryError is on, the path (filename or
directory) of the dump file (defaults to jrockit_<pid>.hprof
in the working directory)
SegmentedHeapDumpThreshold = 2G (default, writeable)
- Generate a segmented heap dump (JAVA PROFILE 1.0.2 format)
when the heap usage is larger than this
HeapDumpSegmentSize = 1G (default)
- Approximate segment size when generating a segmented heap
dump
StartMemleakOnPort = 0 (default, writeable)
(Alias: -XXmemleak)
- Listen for memleak connections on this port (0 for default)
FlightRecordingDumpOnUnhandledException = false (default, writeable)
- Generate a Flight Recording dump when a thread is terminated
due to an unhandled exception
FlightRecordingDumpPath = (null) (default, writeable)
- When FlightRecordingDumpOnUnhandledException is on, the path
(filename or directory) of the dump file (defaults to
jrockit_<pid>_<thread id>.jfr in the working directory)
Runtime:
AbortOnCrash = false (default, writeable)
- Abort the JVM in case of an crash.
DumpOnCrash = true (default, writeable)
- Generate a dump of the JVM state in case of a crash.
CoreOnCrash = true (default, writeable)
- Generate a core dump file of the JVM state in case of a
crash.
WaitOnCrash = false (default, writeable)
- Wait for user debugger attach in case of a crash.
AbortOnAssert = true (default, writeable)
- Abort JVM on assertion
CrashOnAssert = false (default, writeable)
- Crash dump the JVM on assertion
WaitOnAssert = false (default, writeable)
- Spin and wait JVM on assertion
NumaMemoryPolicy = (null) (default)
- Numa memory policy (interleave, preferredlocal, strictlocal)
BindToNumaNodes = (null) (default)
- Bind process to Numa nodes
BindToCPUs = (null) (default)
- Bind process to CPUs
UseFastTime = true (default)
- Force/disable usage of hardware platform support for fast
time
UseJNIPinning = true (default)
- Use pinning for Objects in call to GetPrimitiveArrayCritical
etc
|
下面?X的输出：
SUN JDK 6
-Xmixed mixed mode execution (default)
-Xint interpreted mode execution only
-Xbootclasspath:<directories and zip/jar files separated by ;>
set search path for bootstrap classes and resources
-Xbootclasspath/a:<directories and zip/jar files separated by ;>
append to end of bootstrap class path
-Xbootclasspath/p:<directories and zip/jar files separated by ;>
prepend in front of bootstrap class path
-Xnoclassgc disable class garbage collection
-Xincgc enable incremental garbage collection
-Xloggc:<file> log GC status to a file with time stamps
-Xbatch disable background compilation
-Xms<size> set initial Java heap size
-Xmx<size> set maximum Java heap size
-Xss<size> set java thread stack size
-Xprof output cpu profiling data
-Xfuture enable strictest checks, anticipating future default
-Xrs reduce use of OS signals by Java/VM (see documentation)
-Xcheck:jni perform additional checks for JNI functions
-Xshare:off do not attempt to use shared class data
-Xshare:auto use shared class data if possible (default)
-Xshare:on require using shared class data, otherwise fail.
The -X options are non-standard and subject to change without notice.
|
JRockit JDK 6
-Xbootclasspath:<directories and zip/jar files separated by ;>
set search path for bootstrap classes and resources
-Xbootclasspath/a:<directories and zip/jar files separated by ;>
append to end of bootstrap class path
-Xbootclasspath/p:<directories and zip/jar files separated by ;>
prepend in front of bootstrap class path
-Xgcprio:[throughput|pausetime|deterministic]
sets priority for the garbage collector (gc)
throughput optimizes the gc behavior to achieve optimal
throughput (default in server mode)
pausetime optimizes the gc behavior to achieve minimal
pause times
deterministic optimizes the gc behavior to ensure extremely
short pause times and limit the total number of
those pauses within a prescribed window (this
feature requires a valid license)
-Xgc:[singlecon|gencon|singlepar|genpar]
used to set a static garbage collector
will override the -Xgcprio option
singlecon use the single-spaced concurrent garbage
collection algorithm (default in client mode)
gencon use the generational concurrent
garbage collection algorithm
singlepar use the single-spaced parallel
garbage collection algorithm
genpar use the generational parallel
garbage collection algorithm
-Xms<size>[g|G|m|M|k|K]
sets the initial Java heap size (ms)
server mode: the default value is 25% of the amount
of free physical memory in the system
up to 64 MB with a minimum of 8 MB (default)
client mode: the default value is 25% of the amount
of free physical memory in the system
up to 16 MB with a minimum of 8 MB
-Xmx<size>[g|G|m|M|k|K]
sets the maximum Java heap size (mx)
server mode: the default value is the smallest of 75% of
physical memory and 1536 MB (default)
client mode: the default value is the smallest of 75% of
physical memory and 64 MB
-Xns<size>[g|G|m|M|k|K]
sets the initial Java nursery size for generational collectors
server mode: the default value is dynamic (throughput
prio and genpar gc) or 10 MB per hardware
thread (pausetime prio and gencon gc)
client mode: the default value is 2 MB
-Xss<size>[g|G|m|M|k|K]
set initial stack size
-Xpausetarget=<optimal_pause_time>[ms|s]
JRockit will optimize the pause time to the given target,
uses -Xgcprio:pausetime
ms pause time specified in milliseconds (default)
s pause time specified in seconds
-Xnoclassgc
disable class garbage collection
-Xdebug
enables debugging support in the VM
-Xrun<library>
loads and runs a library
-Xmanagement
enable the management agent
-Xnoopt
do not optimize code
-Xstrictfp
always use strict floating point calculations
-Xverify
do full bytecode verification
-Xnohup or -Xrs
JRockit will not process CTRL_LOGOFF_EVENT or SIGHUP events
-Xverbose[:memory|load|jni|cpuinfo|codegen|opt|gcpause|gcreport]
Enables verbose output. These are only a few of the
available log modules. For more information on log
modules refer to the documentation.
-Xverboselog:<file>
logs verbose output to a file
-Xverbosetimestamp
adds a timestamp to the verbose printout
-Xverbosedecorations:<decorations>
adds <decorations> to the verbose printout
-Xcheck:jni
perform additional checks for JNI functions
For more information on these options refer to the documentation.
The -X options are non-standard and subject to change without notice.
|
IBM JDK 6
以下选项是非标准选项Q可随时更改Q而不另行通知?
-Xbootclasspath:<path> 引导类路径讄?<path>
-Xbootclasspath/p:<path> ?<path> 附加在引导类路径前面
-Xbootclasspath/a:<path> ?<path> 附加到引导类路径后面
-Xrun<library>[:options] 装入本机代理E序?
Q不推荐Q赞成?-agentlibQ?
-Xshareclasses[:options] 启用cL据共享（使用帮助获取详细信息Q?
-Xint 仅运行已解释的（{同?-Xnojit -XnoaotQ?
-Xnojit 用 JIT
-Xnoaot 不运行预~译代码
-Xquickstart 通过延迟优化来减启动时?
-Xfuture 启用最严格的检查，预测未来的缺省?
-verbose[:{class|gcterse|gc|dynload|sizes|stack|debug}]
-Xtrace[:option,...] 控制跟踪使用 -Xtrace:help 以获取更多详l信?
-Xcheck[:option[:...]] 控制查?-Xcheck:help 以获取更多详l信?
以下选项的参C字节为单位?
带有后缀“k”（千）或“m”（兆）的gq行相应的计?
-Xmca<x> ?RAM cL增量讄?<x>
-Xmco<x> ?ROM cL增量讄?<x>
-Xmn<x> 初始／最大新I间大小讄?<x>
-Xmns<x> 初始新I间大小讄?<x>
-Xmnx<x> 最大新I间大小讄?<x>
-Xmo<x> 初始／最大旧I间大小讄?<x>
-Xmos<x> 初始旧I间大小讄?<x>
-Xmox<x> 最大旧I间大小讄?<x>
-Xmoi<x> 旧I间增量讄?<x>
-Xms<x> 初始内存大设|ؓ <x>
-Xmx<x> 内存最大大设|ؓ <x>
-Xmr<x> 记住的集合大小讄?<x>
-Xmrx<x> 记住的集合的最大大设|ؓ <x>
-Xmso<x> 操作系l线E堆栈大设|ؓ <x>
-Xiss<x> 初?java U程堆栈大小讄?<x>
-Xssi<x> ?java U程堆栈增量讄?<x>
-Xss<x> 最?java U程堆栈大小讄?<x>
-Xscmx<x> 新׃nc高速缓存的大小讄?<x>
-Xscminaot<x> ؓ AOT 数据保留的最共享类高速缓存空间设|ؓ <x>
-Xscmaxaot<x> 允许用于存?AOT 数据的最大共享类高速缓存空间设|ؓ <x>
-Xmine<x> 堆扩展的最大设|ؓ <x>
-Xmaxe<x> 堆扩展的最大大设|ؓ <x>
以下选项的参C 0 ?1 的小数表C?
gؓ 0.3 表示h癑ֈ比ؓ 30%
-Xminf<x> GC 之后自由堆的最百分比
-Xmaxf<x> GC 之后自由堆的最大百分比
以下选项的参C数表示?
-Xgcthreads<x> 讄 GC U程的数?
-Xnoclassgc 用动态类卸装
-Xclassgc 启用动态类卸装
-Xalwaysclassgc 启用每个 GC 的动态类卸装
-Xnocompactexplicitgc 用pȝ GC 的压~?
-Xcompactexplicitgc 启用每个pȝ GC 的压~?
-Xcompactgc 启用压羃
-Xnocompactgc 用压羃
-Xlp 启用大页面支?
-Xrunjdwp:<options> 启用调试QJDWP 标准选项
-Xjni:<options> 讄 JNI 选项
|
]]>
JRockit GC in Action
In this article I would like to elaborate on the garbage collection specifics of Oracle's JRockit JVM. Recently JRockit has been made free for use and many people may consider using it instead of another widely popular Oracle JVM - HotSpot (former Sun's JVM). I have more experience with HotSpot JVM, so my opinion may be biased a little, but I will try to stick to the facts as much as I can.
Disclaimer: This article expresses my personal opinion based on my practical experience with JRockit and HotSpot JVMs. My experience is limited by few use cases. Conclusions from this article may not be valid for other use cases. I'm not pretending that I have completed comprehensive research of JRockit's GC behavior.
JRockit garbage collection algorithms
JRockit uses mark-sweep-compact (MSC) as its base garbage collection algorithm, though it allows a lot of tweaking. The JVM command line option -Xgc: allows to choose variations of MSC algorithm. The following variations are available in JRockit R28:
| -Xgc: option | Generational | Mark | Sweep |
| genconcon or gencon | concurrent | concurrent | |
| singleconcon or singlecon | concurrent | concurrent | |
| genconpar | concurrent | parallel | |
| singleconpar | concurrent | parallel | |
| genparpar or genpar | parallel | parallel | |
| singleparpar or singlepar | parallel | parallel | |
| genparcon | parallel | concurrent | |
| singleparcon | parallel | concurrent |
There are also special values for -Xgc: (prior to R28 -XgcPrio: was used for this) options which instruct the JVM to use heuristics to choose best algorithm in run-time (unlike HotSpot JRockit can switch algorithms while the JVM is running, though documentation says that R28 is likely to stick with one algorithm).
- -Xgc:throughput - best throughput,
- -Xgc:pausegen - minimal pauses,
- -Xgc:deterministic - minimal pauses, stable pause time.
Generational vs single space
In my previous article , I explained the idea behind generational garbage collection. The generational approach assumes that space is divided into young and old space, each of which are collected by different algorithms (young space employs copy collector, while old space more sophisticated mark-sweep-compact). Keeping young and old space separate, requires the JVM to implement some kind of barrier to track old-to-young references. In generational mode JRockit uses a card marking barrier similar to one in HotSpot's CMS and throughput collectors (HotSpot's G1 is the only mainstream collector using other type of barrier). Unlike HotSpot which is always using generational approach, JRockit can operate in single space mode. Single space mode means:
- no young collection pauses,
- no write barrier unless it is needed for old space collector,
- more frequent old collection pauses,
- orders of magnitude worse throughput compared to generational collector.
Parallel vs concurrent
Parallel collectors require stop-the-world pause for the whole duration of major collection phases (mark or sweep), but employ all available cores to compress pause time. Parallel collectors usually have better throughput, but they are not a good fit for pause critical applications. Concurrent collector tries to do most work concurrently (though it also does it in parallel on multi-core systems), stopping the application only for short duration. The concurrent collection algorithm in JRockit is fairly different from both HotSpot's concurrent collectors (CMS and G1). I will explain how it works in details later in this article.
A Few differences between JRockit and HotSpot
Heap geometry
The HotSpot JVM has fixed heap geometry, in particular young, tenured and permanent spaces have fixed address ranges during the JVM life time (though physical memory may be partially committed). On the contrary, JRockit has single heap space. If a generational collection algorithm is used, some part of this space will be used for nursery (young space), though nursery in JRockit is not necessary continuous. The same is true for keep space (equivalent of survivor space in HotSpot). Both nursery and keep space may drift in the heap during JRockit's JVM life time. JRockit has no analog of HotSpot's permanent space.
Aging of objects in young space
HotSpot keeps the exact age (in terms of survived collection) associated with each object in young space. Using this knowledge HotSpot can keep an object in young space through several collections, which is an effective way to fight medium-aged garbage without increasing young space (though increasing young space is usually better in terms of performance). JRockit does not keep objects age, so objects are always promoted on second collection (first collection will move object to keep area, and second to old space).
Thread local allocation blocks and pauses
Both HotSpot and JRockit use TLABs (thread local allocation blocks) for fast object allocation. TLABs are allocated in young space/nursery (in single space mode, JRockit allocates TLABs in old space). Threads allocate new objects in their TLABs, and when a TLAB gets full, the thread requests a new one from the memory manager.
In HotSpot, all TLABs are recycled during young space collection (which is usually triggered by particular thread requesting TLAB block). JRockit is different, failure to allocate a new TLAB will trigger young GC, but it is not guaranteed that GC will start immediately or that GC will free enough continuous memory for TLAB. In later cases, the thread will be blocked waiting for TLAB while the JVM technically is not in stop-the-world pause. In other words, JRockit has two types of application pauses: stop-the-world pauses and TLAB wait pauses (affecting individual threads). From an application point of view, thread pauses are as bad as stop-the-worlds ones. It is impossible to guarantee service of application if random threads are blocked. The JVM may not fairly report TLAB wait pauses, so it is possible that application will experience pauses not reported by GC logs.
Concerning TLAB sizes, HotSpot is more aggressive for growing TLABs compared to JRockit. JRockit is more conservative because TLABs may survive several young collections. HotSpot recycles all TLABs in each young collection, so large TLABs are not going to be wasted if the thread would stop actively allocating objects.
JRockit's concurrent collector
JRockit has a very sophisticated concurrent collector. It is a variation of mark-sweep-compact algorithm. During mark phase, collector is traversing object graph marking all reachable objects. During sweep phase, whole heap is scanned and space from non-marked objects is reclaimed. Compact phase relocate objects in heap, fighting with fragmentation. JRockit can execute mark and sweep phases in concurrent mode. Concurrent implementation of mark phase requires breaking it into 3 sub phases:
- initial mark - stop-the-world pause to collect root references,
- concurrent marking - traversing graph without blocking application,
- remark - stop-the-world pause needed to account changes made by application during concurrent phase. During remark collector only have to revisit references changed since initial mark (card marking write barrier allow to do it efficently).
Concurrent marking is fairly straight forward. Sweeping also can be done concurrently with application (JRockit is using two short stop-the-world pause for sweeping, while HotSpot's sweep phase is fully concurrent). But if we just mark unused objects as free space it would eventually lead to fragmentation of heap and inability to allocate objects of moderate size, even if free space is available (death by fragmentation). JRockit is using compaction to protect itself against fragmentation.
Compaction is a very expensive operation. The JVM should move not only the object itself, it should also update all references to every relocated object. Compaction also requires stop-the-world pause and is single threaded in JRockit JVM. To avoid long compaction pauses, the garbage collector can do compaction incrementally. Each time when concurrent collection is stated, the JVM selects a range of heap space to be compacted. During the mark phase all references to objects in compaction area are collected. During the sweep phase, unreachable objects are marked as free space. And finally during the compact phase objects in compaction area are relocated. Compaction can be either internal (objects are relocated inside of compaction region), or external (objects are copied out to another region and whole old region becomes a free space). Compaction phase is abortable, JVM may choose to abort compaction half way if it is taking too much time. JVM may also decide not to move some objects if they have too many external references (or if they are pinned).
Even done incrementally compaction is significantly increasing pause duration. It is possible to turn off compaction altogether, but this way fragmentation becomes serious treat (unlike HotSpot's CMS, JRockit is not using free lists and statistical analysis to control fragmentation of heap).
JRockit's gencon vs HotSpot's CMS quick summary
Both use 4 phase concurrent marking (initial mark, concurrent sweep, concurrent preclean, remark). HotSpot's CMS is using fully concurrent sweep (without compaction).
JRockit may use compaction, compaction requires additional pause.
In JRockit initial mark and remark are forcing young collection. In HotSpot it is more flexible. Initial mark may wait for next young GC, while remark either force it or scan objects in Eden without young GC.
HotSpot's CMS is using free lists and statistical analysis to avoid fatal heap fragmentation. JRockit can do compaction, but very prone to fragmentation if compaction is not frequent enough.
Configuring JRockit for low pause on large heap
Garbage collection tuning is very application specific. So everything below has been written with certain type of applications in mind. Application class I'm interested in is same as in previous article. Its key characteristics are:
- Heap is used to store data structures in memory.
- Heap size 10GiB and more.
- Request execution time is small (up to dozens of milliseconds).
- Transactions are short (up to hundreds of milliseconds). Transaction may include several requests.
- Data in memory is modified slowly (e.i. we do not modify whole 10GiB in heap within one seconds, though updating of 10MiB data in heap per second is ok).
- Amount of short lived garbage is fairly large ~100-200MiB sec (garbage produced by parsing encoding network protocol, etc).
We have to for gencon algorithm and tune it by hands.
Sizing young space
Default size of young space in JRockit is 10MiB multiplied by number of young collection threads (young collection is done in parallel). Usually this default size is too small and you would want to increase it to reduce young GC frequency (-Xns<size> JVM option will help you). Compared to HotSpot, JRockit young space collection pauses are considerably shorter.
Keeping compaction pauses under control
JVM can abort compaction if it is taking too long. This is effective way to ensure max pause guaranty. Unfortunately you cannot just say -XpauseTarget=50 and relax. JRockit forbids pause target below 200ms if GC type is not set to deterministic, but if you use -Xgc:deterministic, JVM will choose singlecon mode and you will enjoy 5-30 second pauses (dependent on heap size) due to lack of throughput. This is really sad.
Due to pause target is locked out from our use, we have to use other options. There are too ways how we can prohibit long compaction:
- limiting size of compaction area (using -XXcompation:percentage=n option),
- limiting number of references to be updated during compaction (using -XXcomaption: maxReferences=n).
Running on 32GiB heap, good, bad and ugly.
Now I would like to share my experience of running 32GiB Oracle Coherence node on JRockit. Though I have spent enough time with tuning of GC options, there is still a fair chance that I have missed something. So please take my opinion with a grain of salt.
Good, young GC pause times
Young GC pause time are much better than HotSpot's CMS. It is roughly on par with patched version of JDK7 (even slightly better). Young collections are most frequent ones, this is really good that JRockit can handle them so well.
Bad, throughput
It is just not enough. I believe it is a curse of any compacting collector (HotSpot's G1 included). Modern hardware is just not enough to do all work associated with object relocation fast enough. But lack of throughput may not necessary be a show stopper. While my tests are fairly write intensive, for many applications JRockit's generational collector throughput may be enough.
In terms of throughput HotSpot's CMS beats out all competitors (probably except Azul Zing, which is using some intimate access to hardware not possible for common JVMs like HotSpot or JRockit).
Bad, fragmentation
Surprise! Compacting collector is prone to fragmentation. Combination of low throughput and incremental compaction leads to a fragmentation. Increasing throughput probably would remedy this problem, but it is impossible without significant increase in pause duration. Another way to counter fragmentation is increasing heap size, but this approach also have obvious practical limitation.
Ugly, long pauses
If you are looking only at logs of JRockit's GC, you may be kept under the assumption that pauses are short and low throughput is the only issue. It is not true. Your application may experience pauses not reported by JVM. You can easily measure them in your application code, though. After spending some time investigating this problem, I came to conclusion that the concurrent preclean phase is hindering young collection.
Normally young collection starts immediately, if TLAB cannot be allocated. But if concurrent preclean is active at the same time, it seems that the young collection can be delayed (and this delay can be significant 0.5-2 seconds depending on preclean phase duration). During that time threads are blocked waiting for TLAB. TLABs are usually small enough, so you have a good chance that most worker threads of your application will be blocked waiting for TLAB allocation. This is as severe as normal stop-the-world pause except, JVM does not report anything.
Why is preclean is affecting young collection? It is a good question, one possible reason is that remark which is scheduled after preclean requires young collection anyway, and the JVM thinks that this way it can avoid 2 pauses. Or it may be young collection interferes with concurrent preclean somehow using sharing data structures, so the JVM decides to delay it. The reason is not clear for me, but the consequence is unpredictable long application pauses which cannot be controlled.
This behavior is a serious show stopper for using JRockit in pause sensitive applications.
Deterministic pauses myth
JRockit claims what it can guarantee deterministic short pauses (below 50ms). This claim is absolutely valid. Single space concurrent collector, fully controls duration of pauses, so it can provide this guarantee. The problem is extremely low throughput though. Throughput can be increased by throwing in more memory for the application. But it will probably require tens or even hundreds times memory overhead to provide throughput comparable to the generational collector.
Conclusion
JRockit is a nice product, it has a lot of advanced features and is a very mature JVM. But so far I'm not going to use it for response time sensitive applications. Still I believe JRockit has good potential. There may also be kinds applications which can benefit from JRockit's garbage collection algorithms better than typical data grid.
Anyway it is good to have fair competition in the JVM area. Good luck to both JRockit and HotSpot products!
See also
Some of my other articles about garbage collection.
]]>
声明:本站WebLogic文章同步整理到老刘文库.
来源Q?/b>http://allthingsmdw.blogspot.com/2012/02/multicast-vs-unicast-with-weblogic.html
THURSDAY, FEBRUARY 9, 2012
Multicast Vs. Unicast with WebLogic Clustering
WebLogic Clusters manage membership via messaging within its members. The members join/leave the cluster as well as update other members via messages to the entire cluster. There are two ways for cluster messaging in WLS - Multicast or Unicast. This post goes provides a brief overview of the cluster messaging and some general guidelines around using the different messaging options.
WLS Cluster
WebLogic clustering provides a homogeneous model for managing a set of server instances while providing scalability, load balancing and high availability to the services running within the member instances. For the end client, it appears like one single and uniform service with all the RASP (reliability, availability, scalability, performance) capabilities. Each cluster member is aware of other members and advertise each other services in addition to their own. Refer tohttp://docs.oracle.com/cd/E11035_01/wls100/cluster/failover.html for more details on replication and failover of clustered services.
Unicast & Multicast
Multicast is easier to explain over Unicast. Multicast is a broadcast UDP option for sending a packet/announcement over to a group that is listening on a specific multicast address and port over which the announcement is sent.There is a defined range for valid Multicast address (224.0.0.1 to 239.255.255.255). Everyone listening on the given address hears the announcement just like following a Twitter post. Some limitations with Multicast is the TTL (time to live) across machines/subnets/routers needs to be adjusted and the routers configured to retransmit the multicast packet across subnets. More details on the weblogic specific multicast configurations can be seen in my Exalogic and Multicast blog post.
Unicast is more of a point to point UDP option to send the packet to a specific member and not everyone. That way, unicast is more of a private conversation between two individuals while multicast is more of a shout to a group or room. Both are UDP based, so there can be losses unlike TCP that handles retransmissions on message loss. But Unicast can span across routers and does not have to worry about TTL without the everyone hearing the announcement. So, Network Admins in general prefer to go with Unicast over Multicast for these reasons.
WLS Cluster Configuration
When a cluster is created within a WLS Domain (either via wlst or config wizard or copy/update of existing domain), it is configured as using Unicast or Multicast messaging. As part of complete Cluster configuration, the multicast listen address and port should be specified if going with Multicast option. Also the managed servers should be targeted/added to the Cluster instance. There can be multiple clusters and any given managed server instance can only belong to atmost one cluster (or none). This will let the clustered managed servers (Admin Server should not be part of any cluster nor can cluster span domains) go with Unicast or Multicast when they are started. It should be noted that Multicast used to be the only option in WebLogic prior to 10.0 version while either Unicast or Multicast can be used from version 10 onwards.
Cluster Messaging
How does each member join the cluster and see or recognize others? At bootstrap time, the managed servers get their configuration via JMX MBeans from the Admin server (or from cached configurations if the Admin server was down) and recognize that they belong to a cluster and they have to go with Unicast or Multicast.
WLS Multicast Messaging
So, in a multicast messaging cluster, the managed servers start listening to the specified multicast address once it checks its configuration and knows it belongs to so and so cluster and has to use specified multicast address and port. Once it listens on the specified multicast address, it sends an announcement about its arrival to others via multicast - more like a shout-out. Other running clustered members of the same cluster who are already listening will respond back and add the new member to their list of known cluster members. The new member will also update its cluster list with other members. This process continues as new members get added. The membership gets renewed based on each member sending periodic announcements to other members proclaiming its liveliness. If a member goes down (shutdown or killed or not able to respond), then it wont be able to send its broadcasts and other members will drop it from the cluster list and re-add it when it comes back online. If a member is directly talking to another cluster member, just the direct socket connection is enough in establishing its membership with its connected member. Since multicast is a broadcast, just a single announcement is retain a instance's membership and let others continue to maintain it in their cluster list till its time to renew its membership. Its a mesh where every member can see every other member in the cluster.
WLS Unicast Messaging
With Unicast, WLS divides the cluster into a multiple groups, each having a max of 10 members. The division happens as the servers come up. Each of the server listens on their specified listen address and the other members can send/receive unicast packets over that listen address as every clustered member knows the configurations of other cluster members.
The oldest within the group is designated the group leader. The group leader communicates over Unicast to other members (over the specified member's listen address) within its group and adds/drops them based on them renewing their membership or not responding. The group leaders communicate amongst themselves. So, if there are 4 group leaders, each group having 10 servers, a membership announcement from server1 in group1 will be picked by GroupLeader1 of group1 and retransmitted to all other members within the group1 as well as to other three group leaders. The remaining group leaders will in-turn retransmit the membership information within their groups. This way, every change is picked up and retransmitted by the group leaders to within their group and to other groups via group leader to group leader communication. The group leaders remain the hub for each group while they themselves form a mesh with other group leaders.
Comparison between Unicast & Multicast
| Multicast | Unicast |
| Only option in pre-10.0 versions of WLS, continues to exist in version 10+ | Available from version 10 onwards |
| Requires configurations to Routers, TTL | No configuration required |
| Requires configuring the Multicast Listen Address and port | Just specify the listen address (can be Default Channel or use a Custom Network Channel for Cluster communication) |
| One announcement to join/maintain membership | one transmission to group leader has to be retransmitted to other group members (N) + to other group leaders (M) who then again retransmit to their group members resulting in (NxM) packets |
| Everyone sees everyone | Group Leaders have to do real heavy lifting of retransmitting every thing across its group and other group leaders and can get bogged down in just retransmitting |
| Can lead to big broadcasts through the entire subnet/LAN if there are frequent joins/drops of members or change in services (JNDI updates of bound services, frequent app deployments or members going out of sync) | Not a broadcast throughout the subnet/lan, but still more packets to be sent across as Group Leaders have to retransmit everything. Can consume bigger bandwidth |
As listed in the table above, these would be my guidelines:
1. If the cluster is small and simple (under 20 members), go with Unicast. No configurations required and the group leaders wont be stretched retransmitting data.
2. If the Network configurations strictly prohibit multicast and members have to reside in different subnets and cluster sizes are still under or mid-20s, go with Unicast.
3. If its a real large cluster (over 20 members) and members can reside in the same subnet or even if they are not on same subnet but network router configurations can allow multicast, go with Multicast.
4. If over 50 members, change to network configurations to allow multicast and stick with Multicast.
5. Over 100 members, try to break up the domain into multiple separate domains and individual clusters for better administration and management even though Multicast option can handle such large domains. Or use custom scripts/wlst to manage and monitor individual members instead of relying on a single application (like console) to manage/monitor/handle all servers at the domain level.
The reason for recommending Multicast over Unicast for large clusters is due to the work load on the group leaders and retransmissions. The group leaders have to retransmit every member's packet within their group as well as to other group leaders (who again send to their group members) which can just lead to more and more work as the cluster grows bigger.
Another big reason is that WLS Multicast based messaging is quite mature and stable compared to Unicast which got only introduced with version 10. Also, with unicast, there can still be retransmits (as its not auto error correcting) and it can consume more bandwidth due to repeat retransmits by group leaders to others compared to one transmit for multicast.
Conclusions
I hope this article helps clarify the internal working of WLS Cluster membership around Unicast vs Multicast messaging while providing some guidance on the option to use based on requirements and constraints.
Posted by Sabha Parameswaran at 12:33 PM
]]>
文档:http://www.oracle.com/technetwork/middleware/weblogic/documentation/index.html
此次同时发布的还?em>Oracle Fusion Middleware 11g R1 (11.1.1.6.x),包含下列产品:
- Oracle WebLogic Server 11g R1 (10.3.6)
- Oracle SOA Suite 11g R1 (11.1.1.6.0)
- Oracle Business Process Management 11g R1 (11.1.1.6.0)
- Oracle Complex Event Processing 11g R1 (11.1.1.6.0)
- Oracle Service Bus 11g R1 (11.1.1.6.0)
- Oracle Enterprise Repository 11g R1 (11.1.1.6.0)
- Oracle Service Registry 11g R1 (11.1.1.6)
- Oracle Application Integration Architecture Foundation Pack 11g R1 (11.1.1.6.0)
- Oracle Data Integrator 11g R1 (11.1.1.6.0)
- Oracle WebCenter Portal 11g R1 (11.1.1.6.0)
(previously known as Oracle WebCenter Suite) - Oracle WebCenter Content 11g R1 (11.1.1.6.0)
(previously known as Oracle Enterprise Content Management) - Oracle Identity Management 11g R1 (11.1.1.6.0)
- Oracle Forms, Reports, Portal & Discoverer 11g R1 (11.1.1.6.0)
- Oracle Traffic Director 11g R1 (11.1.1.6)
- Oracle Repository Creation Utility 11g R1 (11.1.1.6.0)
- Oracle JDeveloper & Application Development Framework 11g R1 (11.1.1.6.0)
]]>
]]>
by WebLogic中文博客站长刘长?BeanSoft@126.com)
支持Tomcat 5.0,5.5,6.0, JDK 1.4,1.5,1.6
http://beansoft.biz/
本Y件具有Tomcat Manager应用的全部功能ƈ增加了相关信息的监控功能Q本人开发的中文语言包和使用说明文档收费Q原英文版Y件可从互联网下蝲?/p>
最新版本：1.7b
许可Q开?/p>
操作pȝQJava 跨^収ͼ支持Tomcat 5, 6
下蝲地址及详l中文用说明文档：发送邮件到beansoft@126.com联系购买?/p>
q行截图Q?/p>
]]>
一q137文章，已经上传完毕Q除个别文g因命名问题外上传p|Q?5%的文章已l可以直接浏览或打包下蝲了。WebLogic中文博客目前正在致力于新版本的通用Java中间件监控Y件的研发中（单一软g支持Tomcat, Resin, JBoss, WebLogic, WebSphereQJVMq行状态监控等Q，因此q期不会发表新的技术文章。如果您需要这些文章的word版本Q请联系本h购买Q?a href="mailto:beansoft@126.com">beansoft@126.com 或?QQ 9991483?/p>
下面是所有WebLogic文章索引Q?/p>
2009-11-01 配置 WebLogic Server 11g 集群单服务器版（WindowsQ?pdf
2009-11-06 WebLogic Server 11g节点理器和Machine配置单机版（WindowsQ?pdf
2009-11-06 关于Spring和WebLogic版本兼容的一点小提示.pdf
2009-11-09 WebLogic 11g 如何修改 Console 的端?pdf
2009-12 Weblogic 11 集群和节点管理器配置快速入门视?单服务器?.pdf
2010-01-25 WebLogic各个版本对JDK和Spring的支持度.pdf
2010-03-23 JNDI 讉K外部 WebLogic 11 数据源的操作步骤.pdf
2010-05-07 Oracle WebLogic Server 11g Rel 1 (10.3.3) 发布.pdf
2010-07-15 WLST on Weblogic 8.1下蝲地址(?.pdf
2010-08 WebLogic 9.2.4.0 发布.pdf
2010-08-13 WebLogic 11g 下蝲地址?OEPE所有版本官方下载地址及所有版本文?edoc)阅读下蝲地址.pdf
2010-08-16久违或遗忘的WebLogic Java工具.pdf
2010-08-19 单的HelloWorld Portal 应用(for WLS 10).pdf
2010-08-20韩国wls监控 WLMonitor 2.5 beta 1 英文版下?pdf
2010-08-31 Where to download file wlfullclient.jar.pdf
2010-09-09 WebLogic和JDK版本E_度排行榜.pdf
2010-09-10 WebLogic静默卸蝲与安装[Slient Install and Uninstall].pdf
2010-11-26 WebLogic集群实现HTTP复制的简单步?pdf
2010-12-09 WebLogic Edoc中关于weblogic.Deployer的一点小问题.pdf
2011-02-27 如何修改weblogic默认U程池大?pdf
2011-02-28 如何破解WebLogic理密码.pdf
2011-03 WebLogic如何使用GridLinkq接RAC数据?pdf
2011-04-18 WebLogic散包部v用热加?pdf
2011-05-07 WebLogic 10.3.5正式发布,提供下蝲.pdf
2011-05-22 ZJMS的Weblogic Server Webservice开?pdf
2011-05-22ZJMS的Weblogic Server Webservice开?pdf
2011-07-03 WebLogic 10.3.4支持JDK 7.pdf
2011-07-26借助 SAML 实现 WebLogic Server 9.2 单点d相关文章.pdf
2011-07-28同时使用Oracle Exalogic Elastic Cloud和Exadata Database Machine的SquareTwo Financial公司[转].pdf
2011-07-31 3D立体展示 Oracle Exalogic Elastic Cloud X2-2.pdf
2011-08-03 关于WebLogic Windows 7版本.pdf
2011-08-04 ExaLogic EL X2-2 Edoc在线阅读及下载地址,安装视频.pdf
2011-08-12 WebLogic如何处理socket muxers[转].pdf
2011-08-23 Weblogic 10.3.5?4位Windowspȝ下的安装和配|?pdf
2011-08-24 WebLogic中的监视仪表?图文,视频).pdf
2011-08-26 WEBLOGIC JMS 点对炚w|详?pdf
2011-08-29使用WLST创徏和删除DataSource.pdf
2011-08-30 WebLogic Express是免费的?WebLogic是免费的?pdf
2011-08-30 WLST快速创建单机Domain.pdf
2011-08-31 Solaris下如何安装WebLogic.pdf
2011-09-02使用代理插g时群集中?HTTP 负蝲q问题[转].pdf
2011-09-04 AIX下WebLogic安装操作手册[转].pdf
2011-09-10调试基本WebLogic JDBC问题[转].pdf
2011-09-29 优化WebLogic 8服务器性能参数[转].pdf
2011-10 WebLogic Server Blog 内容收藏.pdf
2011-10-07 DomainHealth 1.0.0 发布.pdf
2011-10-10 使用WLST配置WebLogic密码{略.pdf
2011-10-19 WebLogic NodeManager q程d漏洞补丁下蝲.pdf
2011-11 GlassFish 4.0 视频曝光,控制台酷似WebLogic.pdf
2011-11-09 WebLogic Web 应用映射到根目录.pdf
2011-11-28 如何抓取Thread Dump结.pdf
2011-12 Oracle WebLogic Server 12c (12.1.1)正式发布.pdf
2011-12 WebLogic所有版本Edoc在线阅读及下载地址.pdf
2011-12 转蝲Qweblogic cd载机?pdf
2011-12-02 Weblogic - Socket Muxers in Thread Dumps[转].pdf
2012-01-29各个版本WebLogic所支持的JDK及JavaEE版本.pdf
Accessing JMX for Oracle WebLogic 11g.pdf
BEA Weblogic Server宝典[中文囄版] [PDF].pdf
BEA Weblogic、Tuxedo 下蝲地址[转].pdf
BEA 产品文档[转].pdf
BEA-000337 错误解决[转].pdf
BEA-000402问题解决 but the maximum number of socket reader threads allowed by the configuration is.pdf
BEA公司被收购前所有版本Y件支持的操作pȝ{配|信息列?pdf
chaowang在甲骨文C日的演讲教材下蝲.pdf
Debugging WebLogic Platform Internals.pdf
Enable IIOP and default user for the WebLogic server[转].pdf
Installing Oracle WebLogic Server and Creating a Domain [Linux].pdf
Jython相关文章收藏.pdf
Linux下Weblogic 11g jar格式安装包如何安?pdf
Managing WebLogic servers with JConsole.pdf
Monitoring WebLogic 9 using JMX.pdf
Oracle Fusion Middleware支持的JDK{系l配|列表信?pdf
Oracle WebLogic Integration.pdf
Oracle WebLogic Server 11g Monitor and Tune Performance评介绍[转].pdf
Oracle WebLogic Server Enterprise Edition 报h.pdf
Oracle WebLogic Server Information Center[转].pdf
Oracle官方关于WebLogic服务有效期的文档.pdf
Performance and Tuning for Oracle WebLogic Server 11g[PDF] Download.pdf
Reason of java.lang.InternalErrorQ?erroneous handlers.pdf
startWebLogic.sh启动p|Q提CError initializing Embedded LDAP Server错误.pdf
WebLogic 10.3.4正式发布,提供下蝲,支持JSF 2.0, JPA 2.0和JAX-RS 1.1[图].pdf
WebLogic 10各个版本详细名称.pdf
Weblogic 11g 安装部v手册.pdf
WebLogic 11gR1 PS3所有BEA错误代码详细信息列表.pdf
WebLogic 8 debug flags.pdf
WebLogic 8 监控 wlstat 0.2, 方便监控weblogic的Sockets,jvm,jdbc,threads,session.pdf
WebLogic 8.1 FTP 下蝲地址(Windows版本).pdf
WebLogic 8.1.6 Windows 安装包下?pdf
WebLogic 8.1.6的所有BEA错误代码索引.pdf
WebLogic 9 实现ZOracle数据库的用户w䆾存储CZ代码.pdf
Weblogic 9.2 部v 8.1 下运行的 EAR 出错的部分解x?pdf
WebLogic 9.2的所有BEA错误代码索引.pdf
Weblogic for aix操作手册.pdf
WebLogic JDBC 驱动的配|?pdf
WebLogic JSP Servlet U程时讄参数.pdf
WebLogic Portal服务器配|手?pdf
WebLogic Server 10.3.4 Released ?Key APIs of Java EE 6 and More[转].pdf
WebLogic Server 9 ?Web Service ~程?JWS.pdf
WebLogic Server 9.2 集群配置单服务器?pdf
WebLogic Server 9.2 集群配置单服务器版和多服务器?PDF).pdf
WebLogic Server 9.2 集群配置多服务器?pdf
WebLogic versioned deployment side-by-side[转].pdf
WebLogic 最新版本下载地址.pdf
weblogic.Admin[转].pdf
weblogic.security.internal.encryption.EncryptionServiceExceptionQ?com.rsa.jsafe.JSAFE_PaddingExceptionQ?Could not perform unpaddingQ?invalid pad byte.pdf
weblogic.utils.classloaders.FilteringClassLoader所在包.pdf
WebLogic8.1打印详细的jdbc日志.pdf
Weblogic8.1集群中批量启动和关闭所有服务器的脚本[转].pdf
weblogic9 jdbc日志跟weblogic8的区?pdf
WebLogic公司发展?pdf
WebLogic启用域之间的跨域安全 Enable Cross Domain Security between domains[转].pdf
WebLogic如何强制先加载WEB-INFQlib下的jar.pdf
WebLogic如何更换64位JDK[转].pdf
WebLogic密码恢复Q一Q[转].pdf
WebLogic密码恢复Q二Q[转].pdf
Weblogic的Machine,Server,Domain,Cluster的关p?pdf
WebLogic集群环境下如何访问EJB实现负蝲均衡.pdf
WLS10.3.0中，q接试D的connection pool shrinking(disabling)问题分析[转].pdf
WLST脚本获取ThreadDump[转].pdf
[WebLogic]dev2dev 2004 合订本下?pdf
[转]EJB在Weblogic Server集群中的实现.pdf
[转]WebLogic 10.3.4 新功能：CAT - Classloader分析工具.pdf
[转]WebLogic ClassCastException 错误解析.pdf
[转]WebLogic Server注册为Windows服务.pdf
【{】Weblogic挂v、宕机问题分析及优化.pdf
使用VisualVMq程监控WebLogic服务器JVM.pdf
使用WLST监控应用状态[转].pdf
使用WLST脚本列出JMS队列中的消息.pdf
删除WebLogic 10的缓存[转].pdf
原dev2dev的WebLogic General_֍贴?pdf
如何抓取Thread Dump结.pdf
开发自定义的MBean来管理J2EE应用(W四部分)[转].pdf
惛_WLST中运行本机命?pdf
监控U程执行情况,耗光时自动输出thread内容[转].pdf
单的Oracle WebLogic 11g安装部属手册(PDF).pdf
?多机nodemanager试记&weblogic103.pdf
配置ZCoherence 的WebLogic Server会话理[转].pdf
Weblogic 8.1 JNDI 教程PPT.swf
WebLogic Server 8.1 Performance Tuning Guide(调优中文文档).swf
对WebLogic Server JNDI 启用安全讄.swf
讄WebLogic集群(WebLogic 10 中文文档).swf
]]>
完整的Sun JDK JVM参数可参考官Ҏ?http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html
]]>
http://download.macromedia.com/pub/flashplayer/updaters/9/sa_flashplayer_9.exe
Windows Flash Player 9 Projector content debugger
http://download.macromedia.com/pub/flashplayer/updaters/9/sa_flashplayer_9_debug.exe
]]>
]]>
站长刘长?BeanSoft@126.com)目前p于Oracle。本目前p于Oracle?/p>
本站所有原创内容仅代表站长BeanSoft个h观点, q不代表 Oracle (甲骨文公司及其下属机?的观? 所转蝲内容仅代表原作者观? q不代表本h或者Oracle的观?
本站原创内容没有作者书面许可不得{?/span>。若作者同意{载，必须以超链接形式标明文章原始出处(http://beansoft.biz/), 和作者刘长炯 BeanSoft@126.com?/span>
本站所提到的Java,WebLogic,Oracle,Eclipse{一pd技术名词均为相兛_?l织的注册商标或者专利品名U?
Copyright © 2010~2012, BeanSoft.biz. All rights reserved. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners.
联系站长: beansoft@126.com
]]>
作?/span>: 刘长?BeanSoft@126.com 日期: 2011-11-28 本文环境: JDK 1.5/1.6, WebLogic 9.0 or later
当服务器挂v,崩溃或者性能底下?/span>,需要抓取服务器的线E堆?/span>(Thread Dump)用于后箋的分?/span>. Thread dump提供了当前活动的U程的快?/span>. 它提供了JVM中所?/span>JavaU程的栈跟踪信息 有很多方式可用于获取Thread Dump, 一些是操作pȝ特定的命?/span>. 操作pȝ命o获取ThreadDump: Windows: 1. 转向服务器的标准输出H口q按?/span>Control + Breakl合?/span>, 之后需要将U程堆栈复制到文件中 UNIX/ Linux 首先查找到服务器的进E号(process id), 然后获取堆栈. 1. ps –ef | grep java 2. kill -3 <pid> 注意一定要谨慎, 一步不慎就可能让服务器q程被杀?/span>! JVM 自带的工兯取线E堆?/span>: JDK自带命o行工兯?/span>PIDq做ThreadDump: 1. jps 2. jstack <pid> 使用JVisualVM: Threads 标签?/span>àThreadDump按钮. WebLogic 自带的获?/span> thread dump的工?/span>: 1. webLogic.Admin 工具 a. 打开命o提示W?/span>, 通过q行<DOMAIN_HOME>/bin/setDomain.env讄相关c\?/span> b. 执行下面的命?/span> java weblogic.Admin -url t3://localhost:7001 -username weblogic -password weblogic1 THREAD_DUMP 注意: Thread Dump 会打印到标准输出, ?/span>nohup日志或者进E窗?/span>. 2. 使用 Admin Console a. d Admin Console , 点击对应的服务器 b. 点击Server à Monitoring àThreads c. 点击: Dump Thread Stack 按钮 3. 使用WLST (WebLogic Scripting Tool) connect(‘weblogic?'weblogic1?’t3://localhost:7001? cd(‘Servers? cd(‘AdminServer? threadDump() disconnect() exit() 注意: U程堆栈会保存在运?/span>wlst的当前目录下. 4. 使用utils.ThreadDumper 用法: C:\bea\wlserver_10.3\server\lib>java -cp weblogic.jar utils.ThreadDumper Broadcast Thread dumps disabled: must specify weblogic.debug.dumpThreadAddr and weblogic.debug.dumpThreadPort Exception in thread "main" java.lang.IllegalArgumentException: Port out of range :-1 at java.net.DatagramPacket.setPort(Unknown Source) at java.net.DatagramPacket.<init>(Unknown Source) at java.net.DatagramPacket.<init>(Unknown Source) at utils.ThreadDumper.sendDumpMsg(ThreadDumper.java:124) at utils.ThreadDumper.main(ThreadDumper.java:145) 5. 如果服务器是作ؓWindows服务的方式运?/span>, 误行下列命?/span>: WL_HOME\bin\beasvc -dump -svcname:service-name 其它一些获?/span>Thread Dump的工hjrcmd, jrmc(JRockit VM自带) ,Samurai, JProfiler{?/span>, q可通过JMX~程的方式获?/span>, ?/span>JDK自带CZ代码: $JAVA_HOME\demo\management\FullThreadDump
]]>
针对q个帖子内容略微做一声明Q这个跟帖称本h为所谓的“自U开源技术爱好者”，|友们可以注意到本h的博客标题从来就是BeanSoft's Java BlogQ本Z要关注Java目开发相关领域的内容Q如Java基础QSWTQAJAXQHTMLQMyEclipse{，而不论是否开源，怿MyEclipse是商业Y件没有多h不知道吧Q而本人的电子?a >《MyEclipse 6 Java 开发中文教E?/a>则是|络上最受欢q的Java教程之一Q所以很遗憾本hq开源技术爱好者，博客内容也仅为工作和学习的心得而已。本人博客曾长期位列BlogJava排名W一Q因此原国内开源项目EasyJWebQ此目目前基本已停滞）的开发者蔡世友Q网名大峡）邀h人推q其产品Q在清华大学附近头Q方才见q仅有的一面，此时也顺便碰见过从事原国内CowNew开源项目（此项目疑似已完全消失Q目前已无法打开其官|?a >http://www.cownew.com
Q的杨中U，q是我和此二人的唯一面Q也可以勉强是好友吧，本h对Q何从事研发工作，乐于分n的技术h员都视ؓ好友Q至于此二h选择后箋和传智播客合作，那是其个由，怿M人都无权q涉。鉴于彼时本人博客排名第一Q甚至于q传智播客的员工张孝也前来力邀本h授课q在本站挂蝲链接帮忙招生Q很遗憾当发C智播客不q是个小的低端C会IT培训机构Q学员水q_差不齐，只能听懂HelloWorldQ深了他们听不懂Q课E安排随时调换，师资力量薄弱Q工资待遇差Q兼职ؓ600一天，全职月薪据张孝祥口头讲一般ؓ底薪5KQ其它部分上课了才有课时Ҏ?00一天，周六也要d司备课，不交保险和公U金Q因最l未{同，至于其它员工工资和{正工资到底多，因ؓ公司机密Q本Z得而知Q但q待遇对我毫无吸引力Q我原来公司四险一金都有）Q本察情况后甚是担心留下会降低自己的技术水qI在D3个月后果断离开了，如今在某知名外企工作?/p>
更y的是前一阵子到了当时带的一个学员，他亲口说当时大部分外地来京的学员Q最后都CQ也没有从事IT相关的工作，更间接证实了低端IT培训所存在的一些问题。至于此人提到的学员抗议的问题，低端IT培训都不可能100%的h都满意，只要做到大部分h满意Q这Ҏ是有保证的，否则Zq要l我加课Q这话这不是自相矛盾嘛？换言之如果文中认为本课不好，那ؓ何当时传智播客还一再让我授课，q安排多门课E如UMLQLinuxQStruts2QSCMQLinux{等Q这N不是培训机构误h子弟Q不负责ȝ做法嘛？像课堂上讲课学生情A很大Q学生骂老师的事情，像张孝祥q样的老讲师也遭遇q吧Q而且至今|上依然有h骂张孝祥Q我看张孝祥依然在网上讲译ֽ视频不是吗？至于_“因Z讲课不好Q传智播客网站上的教师队伍中从未出现q此人的姓名。”，q是因ؓ本hq未与其q行长期合作的意愿，而且把兼职讲师列到教师队伍中Q也于理不合。讲课期_张孝一再想让我录课E视频发到网上做q告Q但因ؓ我的W记本不兼容他所l的录屏软gCamtasia Studio的问题，没能如愿Q这个兼职讲师录视频的事情，也是我从事低端社会IT培训和企业培训这么久来第一ơ遇到。但是本是给同学们录制了一部分现场评的录像（BBFlashBack?fbr格式Q作为复习之用，q些视频至今仍在传智内部传。至于“但传智领导想着他也l济情况H迫”这L说法Q我不知道付出劳动获取报酬有什么错误，N传智播客的讲评员工也都是因为经情늪q才去讲课挣qQ也不知道到底是哪位“传智领导”说的这话？
再来看看文中所提：爱好写文档，文档写的很好Q这些都是事实，也是成ؓ高手的一个好办法Q很遗憾本h是一位Java高手。至于免费讲视频Q本Z来就是乐于从事知识分享，谁都知道|上热心|友制作的免费视频很多，本hq址后的新博客beansoft.biz依然有大量的文章和视频可供参考。曾l想从事IT培训也是事实Q只不过对社会低端IT培训的ؕ象了解太，所以才军_去试水。发C智播客有个特Ҏ要兼职老师自己做PPT教材Q案例等文档Q不知道他们Z么当时不提供教材Q，所以本人的Z文档能力独立~写了多部BeanSoft本h保有版权的文档如?strong>SCM目手把手开发文?/strong>》，《Struts 2 PPT》，《Linux讲义》，《UML》，《SCM、DRP目开发》等?strong>在这里给D讲师提个醒，q些自己研发的原创教材，千万不要随便l学生或者其它第三hQ否则你q着盗版到网上到处都下蝲吧，典型案例如本人?strong>SCM目手把手开发文?/strong>》，p冠以传智播客前缀在网上四处都能见C载，当时张孝说把作者去了可以突出公司Ş象，但因为我是兼职，因此q种做法对作者本人来说没有Q何好处，很遗憑ֽ时本人未能深L识到q一炏V就有可能至于基本功q个Q个Z好自p仯高，不过本h目前从事中间件服务器研发工作Q自认还是不低的?/p>
再来说说我对从事培训工作的CSDN旗下传智播客员工张孝的了解Q我?003q毕业vQ一直从事Java相关的项目研发和理Q也从事q企业的内部培训Q直?006q_才听说有个岁C的张孝和孙鑫Q马士兵Q李兴华{h一P录了很多Java的入门学习视频，q些视频听v来湖北口x较重Q讲的也比较中规中矩些，不是很生动，虽然内容据说有些深度。后来看其个人公开的简历也׃事过六年目研发Q其中用Javaq行的项目看hg只有一q时_参考脓吧原文：
之后据业内h士讲其曾在国信蓝点做培训讲师Q至于讲课情늩竟如何不得而知Q目前CSDNq有帖子评论他讲?strong>不备课，讲课不系l?/strong>Q不q时间久q，已无从考证其真实情况：
。这一特点臛_?008q还存在Q就是喜Ƣ在本h讲课的时候，话筒Q大讲特讲其所认ؓ的原理和心得Q以至于被学生多ơ抗议后才Ş手，本h当时发给学员的现E实录视频上Q就有这L真实记录。于2006qCSDN投资开办社会IT低端培训机构传智播客Q张孝祥则作Z位员工入职其中从事培训相兛_作。后来他邀h人前M事兼职培训，在时间不长的接触中，也发C他在Java目开发上的欠~，所以一再力邀本h为其评开发演C项目SCM。至于他C2009q才学会Strutsq录了视频这些，也间接证实了作ؓ曄的程序员Q岁数太大，学不动真是个自然规律?/p>
张孝此人品行如何，我们不能作主观Q何评论，物以c聚、h以群分，q还要看他有没有朋友说vQ他自称“中国Java培训W一人”、Y件编E语a培训师，然而，g却与同样使用~程语言从事研发工作的郝培强先生、老n和本人等都合不到一起去Q而和从事Java培训的讲师马士兵、孙鑫和李兴华等Z合不来，甚至于和同行青鸟、达内、蓝点等培训机构也似乎不甚友好?/p>
我本惛_传智播客l箋保持沉默Q不把本Z传智播客的这些恩恩怨怨告知于众，因ؓq样Ҏ自n的媄响也不好。但是，此h竟然如此挑衅Q我们就不能不给大家一个交待了?/p>
最后一h看看q篇匿名用户发的帖子Q本Z已截图保存做了相兛_?
http://tieba.baidu.com/f?kz=1113350066 地址为百度脓吧传智播客吧Q?/p>
]]>
]]>
原文: http://www.tagtraum.com/gcviewer-vmflags.html
VMFlags
When it comes to garbage collector and memory flags VMs from different vendors differ somewhat. Most flags aren't even properly documented by the usage printout of the VM themselves. This page tries to shine some light on what garbage collection related flags there are and what they are good for. It covers several Sun and IBM JVMs
Disclaimer: Please note that the data presented in this document has been gathered from several publicly available sources. It is a conscious selection of available VM parameters and even though we tried to check most of the facts presented this document may contain errors.
Choosing a VM
Instructs the VM to use the server HotSpot VM. This also implies that default heap sizes and permanent generation sizes are different.
Under 1.5 this option is the default option, if the machine is a server-class machine.
Supported by: 1.3, 1.4, 1.5
Instructs the VM to use the client HotSpot VM. This also implies that default heap sizes and permanent generation sizes are different.
Supported by: 1.3, 1.4, 1.5
Printing Information about GC
Prints out information about garbage collections to standard out. To print the same information to a file, use -Xloggc:<file>
Example:
[GC 325407K->83000K(776768K), 0.2300771 secs]
[GC 325816K->83372K(776768K), 0.2454258 secs]
[Full GC 267628K->83769K(776768K), 1.8479984 secs]
See -Xloggc
Supported by: 1.3, 1.4, 1.5
Prints information about garbage collections to the specified file.
In conjunction with -XX:+PrintGCDetails this is the best setting for the free GCViewer.
Supported by: 1.4, 1.5
Instructs the VM to be more verbose when printing out garbage collecion data. Specifically it does not only tell you that there was a collection, but also what impact it had on the different generations.
This flag is very useful when tuning generation sizes.
In conjunction with -Xloggc this is the best setting for the free GCViewer.
Example:
2.459: [GC 2.459: [DefNew: 3967K->0K(4032K), 0.0141600 secs] 8559K->7454K(16320K), 0.0143588 secs]
Supported by: 1.4, 1.5
-XX:+PrintGCApplicationStoppedTime
Instructs the VM to print out the length of actual collection pauses.
This flag is useful when tuning concurrent collectors.
Example:
Total time for which application threads were stopped: 0.0468229 seconds
Supported by: 1.4, 1.5
-XX:+PrintGCApplicationConcurrentTime
Instructs the VM to print out the amount of time the applications runs between collection pauses.
This flag is useful when tuning concurrent collectors.
Example:
Application time: 0.5291524 seconds
Supported by: 1.4, 1.5
Ensures that timestamps relative to the start of the application are printed in the GC log.
Supported by: 1.4, 1.5
-XX:+PrintTenuringDistribution
Prints details about the tenuring distribution to standard out. It can be used to show this threshold and the ages of objects in the new generation. It is also useful for observing the lifetime distribution of an application.
Example:
5.350: [GC Desired survivor size 32768 bytes, new threshold 1 (max 31)
- age 1: 57984 bytes, 57984 total
- age 2: 7552 bytes, 65536 total
756K->455K(1984K), 0.0097436 secs]
Supported by: 1.3, 1.4, 1.5
Sizing Heap and Generations
Overall maximum heap size. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xmx256m sets the maximum heap size to 256mb
Supported by: 1.3, 1.4, 1.5
Minimum heap size. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xms256m sets the minimum heap size to 256mb
Supported by: 1.3, 1.4, 1.5
Sets the size of the young generation. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xmn64m sets the young generation size to 64mb
Supported by: 1.4, 1.5
-XX:MinHeapFreeRatio=<minimumInPercent>
Sets the minimal percentage of free heap memory that has to be available after a collection. This parameter can be used to influence when the VM is going to request more memory.
Example:
-XX:MinHeapFreeRatio=70
See -XX:MaxHeapFreeRatio
Supported by: 1.3, 1.4, 1.5
-XX:MaxHeapFreeRatio=<maximumInPercent>
Sets the maximal percentage of free heap memory that must at most be available after a collection. This parameter can be used to influence when the VM is going to lower its footprint. In other words it can shrink the heap and therefore memory consumption.
Example:
-XX:MaxHeapFreeRatio=20
See -XX:MinHeapFreeRatio
Supported by: 1.3, 1.4, 1.5
Sets the ratio between young and old generation.
Example:
-XX:NewRatio=3 means that the ratio between the young and old
generation is 1:3; in other words, the combined size of
eden and the survivor spaces will be one fourth of the
heap.
See -XX:NewSize and -XX:MaxNewSize
Supported by: 1.3, 1.4, 1.5
Sets minimum size of the young generation.
Example:
-XX:NewSize=64m sets the minimum size of the young
generation to 64mb
See -XX:NewRatio and -XX:MaxNewSize
Supported by: 1.3, 1.4, 1.5
Sets maximum size of the young generation.
Example:
-XX:NewSize=64m sets the maximum size of the young
generation to 64mb
See -XX:NewRatio and -XX:NewSize
Supported by: 1.3, 1.4, 1.5
Sets size of the survivor spaces in relation to eden.
Example:
-XX:SurvivorRatio=6 sets the ratio between each survivor space
and eden to be 1:6; in other words, each survivor space
will be one eighth of the young generation (not one seventh,
because there are two survivor spaces).
Supported by: 1.3, 1.4, 1.5
Sets the initial size of the permanent generation (where classes etc. are stored). This can be useful for application servers using many EJBs and JSPs.
Example:
-XX:PermSize=64m
See -XX:MaxPermSize
Supported by: 1.3, 1.4, 1.5
Sets the maximum size of the permanent generation (where classes etc. are stored). This can be useful for application servers using many EJBs and JSPs.
Example:
-XX:MaxPermSize=64m
See -XX:PermSize
Supported by: 1.3, 1.4, 1.5
Choosing and Configuring a Collector
Use parallel garbage collection. This collector is also referred to as the throughput collector. It uses a parallel version of the young generation collector. The old (tenured) generation is still cleaned with the default collector.
Under 1.5 this option is the default option, if the machine is a server-class machine.
This option can not be used in conjunction with -XX:+UseConcMarkSweepGC .
Supported by: 1.4.1, 1.5
Use the parallel old generation collector. Certain phases of an old generation collection can be performed in parallel, speeding up an old generation collection.
This option automatically enables -XX:+UseParallelGC .
Supported by: 1.5.0.6
-XX:ParallelGCThreads=<number>
Specifies the number of threads used in parallel garbage collection when -XX:+UseParallelGC is set. By default a system with N CPUs uses N garbage collection threads.
Example:
-XX:ParallelGCThreads=4
Supported by: 1.4.1, 1.5
Instructs the VM to try to keep garbage collection pauses shorter than the specified value in ms.
This option applies in conjunction with -XX:+UseParallelGC and has higher priority than -XX:GCTimeRatio .
Example:
-XX:MaxGCPauseMillis=10
Supported by: 1.5
Sets a throughput goal for the VM. The ratio of garbage collection time to application time is1/(1+<ratio>).
This option applies in conjunction with -XX:+UseParallelGC and has lower priority than -XX:MaxGCPauseMillis .
Example:
-XX:GCTimeRatio=19 sets a goal of 5% of the total time for
garbage collection.
Supported by: 1.5
Instructs the VM to keep track of some statistics and resize both the young and the old (tenured) generation based on the collected data.
This feature is on by default when the option -XX:+UseParallelGC is used.
Supported by: 1.4.1, 1.5
Instructs the JVM to push memory use to the limit. It inspects the machine resources (size of memory and number of processors) and attempts to set various parameters to be optimal for long-running, memory allocation-intensive jobs. This option is recommended for dedicated server machines.
The physical memory on the machines must be at least 256MB before AggressiveHeap can be used.
Beginning with JVM 1.3.1_02 some GC activity is done in parallel.
Beginning with JVM 1.4 this option implies -XX:+UseParallelGC and -XX:+UseAdaptiveSizePolicy .
Supported by: 1.3, 1.4, 1.5
Use concurrent garbage collection. This collector is also referred to as the concurrent low pause collector. It collects garbage in the old (tenured) generation concurrently to executing the application.
Note that this option can not be used in conjunction with -XX:+UseParallelGC . Instead you may combine it with -XX:+UseParNewGC
Supported by: 1.4.1, 1.5
If the -XX:+UseParNewGC option is in use the remark pauses may be decreased with the -XX:+CMSParallelRemarkEnabled option.
Supported by: 1.4.1, 1.5
Instructs the VM to use a parallel collector for the young generation. This option should be used in conjunction with -XX:+UseConcMarkSweepGC .
Supported by: 1.4.1, 1.5
Activates the train garbage collector. Note that development for this collector has been stopped since 1.4.2.
See -Xincgc
Supported by: 1.3, 1.4, 1.5
Activates the incremental (also called train) garbage collector.
See -XX:+UseTrainGC
Supported by: 1.3, 1.4, 1.5
Miscellaneous Settings
Sets the size of the stack. In a server system with many threads lowering the stack size may be advantageous to reduce footprint. If the stack is too small, you will start seeingStackOverflowErrors.
You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xss128k sets the stack size to 128kb
Supported by: 1.3, 1.4, 1.5
Disables calls to java.lang.System.gc().
-XX:SoftRefLRUPolicyMSPerMB=<ms per mb>
Sets the rate at which the VM clears soft references. The rate is expressed in ms per free mb of heap. For the server VM free heap means potentially free heap using the maximum heap size as set with -Xmx in the calculation. For the client VM the free heap is calculated using the actual current heap size.
Example:
-XX:SoftRefLRUPolicyMSPerMB=1000 instructs the VM to allow
softly reachable objects to remain alive for 1s per free mb
Supported by: 1.3.1, 1.4, 1.5
Java 5.0 (1.5) defines a class of machines referred to as server-class machines. These are machines that have 2 or more physical processors and 2 or more gb of physical memory. On server-class machines the Sun JVM starts with altered default settings. These are:
-server -XX:+UseParallelGC
Additionally the initial heap size ( -Xms ) is set to 1/64 of the physical memory, up to 1gb. The maximum heap size ( -Xmx ) is set to 1/4 of the physical memory, up to 1gb.
Note that on server-class 32bit-Windows systems the VM will nevertheless start with the classic client settings, as most 32bit-Windows Java applications are not server applications.
Disclaimer: Please note that the data presented in this document has been gathered from several publicly available sources. It is a conscious selection of available VM parameters and even though we tried to check most of the facts presented this document may contain errors. Also note that the semantics of some of these parameters are different when used with IBM's resettable JVM for the z/OS platform.
Printing Information about GC
Prints out information about garbage collections to standard out.
See -Xverbosegclog
Supported by: 1.3.1, 1.4.1, 1.4.2
-Xverbosegclog:<path to file><filename[,X,Y]>
Prints out information about garbage collections to a file. If the integers X and Y are specified, the output is redirected to X files each containing output from Y GC cycles.
See -verbose:gc
Supported by: 1.4.1, 1.4.2
Sizing Heap and Generations
Overall maximum heap size. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xmx256m sets the maximum heap size to 256mb
Supported by: 1.3.1, 1.4.1, 1.4.2
Overall minimum heap size. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xmx256m sets the minimum heap size to 256mb
Supported by: 1.3.1, 1.4.1, 1.4.2
Sets the initial size of the system heap. Classes in this heap exist for the lifetime of the JVM. The system heap is never subjected to garbage collection. The maximum size of the system heap is unbounded. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xinitsh256m sets the minimum system heap size to 256mb
Supported by: 1.3.1, 1.4.1, 1.4.2
This is a floating point number between 0 and 1, which specifies the maximum percentage of free space in the heap. The default is 0.6, or 60%. When this value is set to 0, heap contraction is a constant activity. With a value of 1, the heap never contracts. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xmaxf0.6 specifies that the heap will be contracted if more
then 60% of the heap are unused.
Supported by: 1.3.1, 1.4.1, 1.4.2
This is a floating point number between 0 and 1, which specifies the minimum percentage of free space in the heap. The default is 0.3, or 30%. The heap grows if the free space is below the specified amount. You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xminf0.3 specifies that the heap will be grown if less
then 30% of the heap are unused.
Supported by: 1.3.1, 1.4.1, 1.4.2
Choosing and Configuring a Collector
-Xgcpolicy:<optthruput|optavgpause|subpool>
Note that the subpool option was introduced in Version 1.4.1 Service Refresh 1 for AIX only.
Setting gcpolicy to optthruput disables concurrent mark. If you do not have pause time problems (as seen by erratic application response times or by analysis of the verbose GC output), you should get the best throughput with this option. optthruput is the default setting.
Setting gcpolicy to optavgpause enables concurrent mark with its default values. If you are having problems with erratic application response times that are caused by normal garbage collections, you can remove those problems at the cost of some throughput when running with theoptavgpause option.
Setting gcpolicy to subpool enables improved object allocation that aims to achieve better performance in allocating objects on the heap. This setting might provide additional throughput optimization because it can improve the efficiency of object allocation and reduce lock contention on large SMP systems. Concurrent mark is disabled when this policy is enabled.
Supported by: 1.3.1, 1.4.1, 1.4.2
Sets the total number of threads that are used for garbage collection. On a system with n processors, the default setting is n.
Supported by: 1.3.1, 1.4.1, 1.4.2
Compacts the heap every garbage collection cycle. The default is false (that is, the heap is not compacted). This is not recommended.
Supported by: 1.3.1, 1.4.1, 1.4.2
Never compact the heap. Default is false.
Supported by: 1.3.1, 1.4.1, 1.4.2
Disables class garbage collection.
Supported by: 1.3.1, 1.4.1, 1.4.2
Miscellaneous Settings
Sets maximum native stack size for any thread.
You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xss128k sets the stack size to 128kb
Supported by: 1.3.1, 1.4.1, 1.4.2
Sets maximum Java stack size for any thread.
You may use k, m and g for kilobyte, megabyte and gigabyte.
Example:
-Xoss128k sets the stack size to 128kb
Supported by: 1.3.1, 1.4.1, 1.4.2
Runs full compaction each time java.lang.System.gc() is called. Its default behavior with ajava.lang.System.gc() call is to perform a compaction only if an allocation failure triggered a garbage collection since the last java.lang.System.gc() call.
Supported by: 1.4.1, 1.4.2
Never runs compaction when java.lang.System.gc() is called. Its default behavior with ajava.lang.System.gc() call is to perform a compaction only if an allocation failure triggered a garbage collection since the last java.lang.System.gc() call.
Supported by: 1.4.1, 1.4.2
Converts Java application calls to java.lang.System.gc() into no-ops.
Supported by: 1.4.1, 1.4.2
]]>
[原]传智播客q是传诈播客: http://my.chinaunix.net/space.php?uid=7471615&do=blog&id=351017
不得不佩服网友们实在是太有才? 点中低端IT培训的死I?
[原]传智播客q是传诈播客Q?/h3>已有 247 ơ阅?2011-06-02 09:42
obug门肖老湿的事件刚qx没几天，传智播客的张孝祥老湿又蹦出来了，很搞W啊。事情的起因是：张老湿Z学生能够扑ֈ一份月?K的工作，帮学生做面试题，q美其名曎ͼq跟C方和老罗研究考题没什么区别。详l信息看q里。老湿Q拜托不要这么弱智好不好——研I考题跟老湿直接帮学生考试性质完全不一P好不Q还有h说张老湿q是分n知识——拜托各位脑D：软g行业的大牛们很多人都很喜Ƣ分享知识，但绝对不会去替h{考试题。黑客精是乐于分nQ但不是乐于替考当枪手?br />很久以来Q我对于IT培训机构培养出来的学生有偏见——现在也如此。在我眼里，IT培训机构除了Q什么都不教。这U观点很极端Q但如果说给了这U机构出来的应聘者机会，那就是剥Z诚信的应聘者的ZQ还ҎD企业招聘成本的增高，那这样对谁都不公q?br />我承认这些培训机构里面还是有些真正的人才的。但首先Q培训机构出来的学生基数比较大，人才比例比较；其次Q能够忍受培训机构的行ؓQ即便是人才Q也会有些x目染。圆滑奸诈的企业d挑剔的面试官会ؓ了一个小比例而去增加自己的成本和工作量吗Q我惻I换作我，我ؓ什么不选择相对安全而又工作量小的方式，选择诚信度看h高一点的应聘者呢Q?br />在此我本不想从道徯度来说什么。谁没有阴暗的一面呢Q谁没有q过~d事呢Q但张老湿先是把自q道d提升C个高度，然后自嘲了下“在别h的媄响下也闯q红灯”，q就没意思了——我你闯不闯红灯，你闯了，道d不会惩罚你，但死可能会把你扑֎l他创办IT培训机构。你道d再高，你也无法否定你曾l犯下的错误。中国hp么搞W，dƢ从道d斚w说事?br />张老湿跟肖老湿有一个共同点Q就是逻辑比较混ؕ——可能是打太极打多了——你跟他讲错误，他跟你讲道dQ你跟他道P他跟你讲责Q……我׃明白了，你丫认个错能死？伟h毛主席都会犯错，N张老湿你更伟大Q?br />CSDN上脑D居多，q就是我从来不去的原因——去多了Q难免会让自׃变成脑残的?/p>
直接导入目到Eclipse? q行src下唯一的一?java文g卛_,使用内嵌HSQLDB作ؓ工作数据的存储引擎,UJava目不依赖Web容器.
参考视? http://family168.googlecode.com/files/%E7%AC%AC%E4%B8%80%E8%AF%BE.rar
jBPM相关学习视频: http://code.google.com/p/family168/downloads/list
下一步的目标是学习Oracle SOA Suite中的 OSB, BPEL ?BPM.
]]>
下蝲地址, 选择GDI模式q羃FPS可得到小体积视频.
BB FlashBack Express
Version: 3.0.0.1905
Released: 07 Jul 2011
Size: 10.8 Mb
Runs On: Windows 7, Vista, XP, 2003, 2000 (32 and 64 bit versions)
]]>
http://tieba.baidu.com/i/171167167?st_mod=pb&fr=tb0_forum&st_type=uname
q位不成熟的发帖? ?月到7? 一直重复的在各个脓吧发表同一主题的帖? q自己顶自己, 甚至节假日也不休? 您真的太辛苦?
]]>
首先, 学员自n的问? 严格? E序员这一职业是需要思考和创造的, 对基的英语和理解能力也有很高要求, q不是靠背熟几段代码和APIp胜Q? 因此对综合实力要求很? 但培训机构抛弃道德底U? 直接其所谓的入学面试题公之于? 只要交钱可以上培训, 甚至公然鼓吹高中生也能干IT, D大批企图投机者自愿受? 参加培训, 但终归出来的q是ơ品, 不符合企业的长远用h要求, 害h宛_, 多数人长q发展缺乏后? 如今, 北大青鸟, 传智播客{低端Y件培训机构，不断遭到一些用人单位封杀其学? 历中直接qo? q也是不得已的选择. 参?Z么我们招聘的时候绝不要传智播客的学生[转]老n-Z么我要反对北大青?/a>
其次, 低端软g培训公司弄虚作假, 推L助澜. W一个问题是师资, 明明是普通程序员, 楞给包装?架构?. 有的机构则列举一大批子虚乌有的师资阵? 招生? 已经赚到了钱. 但是要想赚更多的? p提高׃? 来招更多的学? 因此, 如何帮助学员修改? 伪造工作经? 成了重头戏. q也D众多用h单位杀其学? 因ؓq浪费的是用人单位的金钱和时? 增加了招人的成本和项目开发过E中的风? 至于有h甚至公然或者暗地里替学员做W试? 那就更加的恶? q些培训机构实际上已l成为整个IT业发展的障碍之一.
最? 低端软g培训, 之所以低? 是因Z们培训的都是一些互联网上唾手可得的技?如Spring, Struts, Hibernate, JBPM, Tomcat, Lucence, .NET, PHP, Java, AJAX, MySQL, Ruby, Android), 以开源免费以及官方公开的文档ؓ? q些东西本来到处都有资料可看, 只需要动动手点击搜烦, 然后下蝲, 实验, 可? 至于相关的书c? 书店里更是又便宜又多. 但是Z招生, E草Ҏ金条, 拼命鼓吹自己培训的内Ҏ如何如何高端, 十分的可笑. 既然q些东西大家都会, 学员又有什么核心竞争力可言? 增删Ҏ复制_脓? 所以不要指望能学到什么能保月?0K+的高端技? 用h单位自然也不可能学员开出昂늚工资, 因ؓ, 你们不是不可替代. 有这么多学费的投?Java U?万元左右, 其它U?K左右), 完全可以C个笔记本电脑+N本书c? 在大学里自学完成q些技术的U篏(大三到大四两q多旉, _?. 如果你没有这U学习意识和自学能力, 不{行的话恐怕永q只能做底层码?
作ؓ结, 再讲下高端Y件培? q些培训一般由Apple,Oracle,IBM,MS,Adobe{上怼业面向最l客? 一般以产品和技能培训ؓ? 以实现双赢ؓ目的, q不以就业ؓ导向, 所以相对而言, 高端软g培训是很入流的职?
]]>
今年三月到四月间Q?a style="color: rgb(92,122,153); text-decoration: none" >传智播客的老师张孝发了三Blog?a style="color: rgb(92,122,153); text-decoration: none" >联想利泰的一道做出来q月薪7K的面试题–交通灯理pȝ》、?a style="color: rgb(92,122,153); text-decoration: none" >又一道Y通动?K月薪面试题——银行业务调度系l?/a>》和?a style="color: rgb(92,122,153); text-decoration: none" >累病倒了我两ơ的面试题–移动用戯费统计系l?/a>》。这三篇无一例外的除了分析面试题以外Q都讲述了张孝祥老师怎么辛辛苦苦l学生做好面试题Q让他们M差的故事。不以ؓ耻，反以?/p>
截图来自《联惛_泰的一道做出来q月薪7K的面试题–交通灯理pȝ?br>
tiny:担心{案雷同Q呵呵，张老师知道q是面试题啊?/p>
截图来自《又一道Y通动?K月薪面试题——银行业务调度系l?br>tiny:原来张老师知道企业不喜Ƣ南郭先生，知道代做面试题会损害企业利益啊?/p>
截图来自《篏病倒了我两ơ的面试题–移动用戯费统计系l?br>tiny:张老师真是呕心沥血Qؓ了给学生作弊Q自己都累病了?/p>
本来q三文章，在twitterQ新微博上Q都有很多朋友批评过Q我也批评过几次Q相信经q大家批评，张老师一定会醒悟到自q问题Q改正帮学生作弊q种不可接受的行为?/p>
谁知??9日，张老师又写了一?a style="color: rgb(92,122,153); text-decoration: none" >我从事的软g培训果真是一个很不入的职业吗？》，文章里面他避重就轻，把大家的批评说成了对他培训方法的不认同?/p>
所以我实在忍不住了Q在新浪微博质问了蒋涛几句，因ؓ我知道蒋涛应该是传智播客的主要投资h?/p>
谁知道蒋涛居然如下回{：
后面q有不少争论Q我不多贴了Q我本来把蒋涛老师当作一个前辈一个朋友，没想到居然会q样…?/p>
我在盛大创新院的时候，自己招聘了一个美工，帮别的项目组面试了很多iOS工程师。招聘现在是非常困难的工作，各大招聘|站推荐来的面试者很多都是滥竽充数的Q本来已l够ȝ的招聘再加上培训机构的作弊，招聘来难。与此同Ӟ一个年Mh们去扑ַ作也会变得越来越难。几q前Q培训学校出来的学生可能q是某些公司争抢的目标，但是现在随着培训学校来多Q竞争越来越Ȁ烈，跟企业斗志斗勇的来多Q很多企业早开始直接刷掉有培训学校l历的学生。我本来是不q么l对d的，但是l过张老师q个事gQ我怿大多数看q张老师的blog的技术面试官Q企业HRQ心目中“传智播客”已l进入了黑名单。我们的目的是找到真正的人才Q不是找一个老师牛屄的hQ这个简单的道理Q张老师Q蒋老师Q不需要研I试题你们应该知道。你们现在送一个学生q了企业Q就是未来堵住了其他学生q这个企业的可能性，哪怕未来那个学生是有真材实学的人。企业的技术面试官和HRQ不是撂爪就忘的老鼠?/p>
现在我出来创业做一个小企业。其实我很知道一些小企业的疾苦，当年我和火炬创业做技术咨询的时候，见过很多没有技术背景的创业者，找技术h才非常困难，因ؓ自己没有辨别能力。所以经常招了一个h说v来不错，看v来挺好，l果做了三个月什么也做不出来。在当年瞬息万变的竞争态势下，三个月什么都没做出来Q对创业者打击非常大。他们只能再找一个技术h员，期待三个月后有点l果。这个层面来看，企业你更伤不v啊?/p>
所以，在我的BlogQ我今天严正声明在“张老师道歉q承诺再也不q行q类作弊行ؓ”之前，我的企业Qƈ号召其他的看到我的文章和张老师文章的企业主Q技术面试官QHRQ坚决不招聘M传智播客培训q的学生?/h1>
有h今天在新说Q也许我40岁以后就不会q么看问题了。我_“反之，我年ȝ时候，学生时想法也怸同，但是q纪大觉得诚信可贵越不可~失”。现在传志播客的学生们，你们可以把我当仇ZQ不q期待你们老了以后懂的我今天在讲些什么?/p>
]]>
Z么我要反对北大青?/a>
2010-04-22 00:20 by 老n, 11682 visits
您是否知道最q北大青鸟有什么新dQ嗯Q最q的电脑报发表了“中国IT培训现状大调查之二”一题为“北大青鸟高薪就业迷䏀的文章Q描qC北大青鸟的种U问题。我q里不想用“揭霜y、“黑q”等Ȁ烈的词汇Q但我会全文转蝲q篇文章Q大家可以自己阅读，自行评h。客观地_q篇报道的内Ҏ否属实我不敢打保，但是我愿意相信其中的说法Q因为北大青鸟及其他一些培训机构的学生于我的感觉，真的不敢恭维?/p>
全文请阅? http://blog.zhaojie.me/2010/04/why-i-say-no-to-aptech.html
说实? U种p, 在很多低端IT培训学校普遍存在, 不管是学Java, .NETq是Office. 惛_加培训的可去一睹内容和辩论, 那是相当的激?
]]>
2005q时, 本h接触到几个从辑ֆ培训毕业的学? 工资Uؓ6K. q几个h的照片到现在q在辑ֆ培训的就业明星宣传板? q也是我W一ơ了解到了达内培? a? 2005q之前的培训, 因ؓIT形势较好, 学员素质普遍较高, 都是大中专以上学? q是有不找C6K,7K,8K的工作的, 例如׃到IBM{外? 底薪是8K.
C2007q时, 一大批培训机构纷Uh? 此时, 僧多_少, 北京已经很难招到学生? 大批招收外地或高中毕业生来参加培? 毕业后的学员薪水, 已经降低CU?.5K.
C2008q时, 本h在多家小培训机构现场了解? 因ؓl济危机原因, 月薪2500一大把, 甚至压根找不到工? q是目前已知形势最差的一q? 但是奇怪的? 众多机构依然标榜׃q_薪水4K, 不知道这些数据又是从何而来.
C2009q时, 形势依然不佳, 但就业率E有好{. 不过不要忘记, 2009q房价增涨一倍达?W/q? 房租已经增长很多, 生活成本大幅度提?
C2010q? 房租暴涨, 搜搜新闻有. 新闻上介l说众多学生降低期望? 甚至出现"中国大学生就业报告：p计算机法学找zL?(参?http://learning.sohu.com/20100603/n272534767.shtml), 在这U情况下, 众多低端培训招生出现危机, 为此, 不惜q一步造假, 开始鼓吹只要学了最新的XX评, ׃薪水马上是7K,8K.
W者也对已׃培训生的后箋发展q行了跟t调? 和大多数大学毕业生一? 过50%的h转去其它行业 (因ؓ学不会或者没兴趣), 另一部分h在月薪逐步涨至E前6K,7K以上? 失去发展动力, 而大部分人则涨至4K? 没了下文. 不要忘了北京的生zL本甚? 6K的税后工资约?700? 房租一间?200元以? 一个月吃饭加上交? q最g?0, 那么一个月也得1000, 到底能留下几个钱, 怿q不是什么难的? 在这U情况下, Ҏ谈不上娶ȝ? 买房? 那是做梦!
So why is it? 原因当然是众? 然而其中一个最可能的原因是自学能力? 看不懂英文资?否则也不用去上培训了), D后箋发展乏力. 大Ş势来? 目前IT行业能吸收的E序员有? 不如工厂能吸收的? 因此D供大于求, q时要加薪自然是相当的困?
2011q? ׃泡沫势明显, 部分大的互联|公司对E序员需求旺? 然而很遗憾的就是他们最需要的不是JavaE序? 而是PHP或者JavaScript,CSS高手. 详情参考各门户|站招聘主页卛_.
]]>
]]>
转蝲? 盲目参加所谓的包就?Java 培训, 需谨慎! 现在׃形势实不容乐观, q不是广告和托们能改变的!
26日，由麦可思研I(MyCOS Institute)撰写的?009q河北省大学毕业生就业报告》完成。记者从报告中获悉，原ؓ热门专业的计机U学与技术、英语、国际经与贸易、法学、工商管理连l两q失业严重?br />(博讯 boxun.com)
5专业q箋两年׃严重
麦可思调查的沛_?008届本U各专业大类中，工学毕业半年后就业率最高，?0%Q农?72%)相对较低Q理?86%)、经学 (84%)、医?81%)和法?80%)也均低于沛_?87%)和全国的本科毕业生毕业半q后q_׃?88%)。麦可思调查的沛_?008届高职高专专业大cMQ轻U食品大cL业半q后׃率最高，?0%Q医药卫生大cL业半q后׃率最低，仅ؓ69%Q远低于我省2008届高职高专毕业生的半q后q_׃?82%)?br />沛_?008届本U毕业生毕业半年后失业量最多的10个专业占了本U失业量?6.2%Q其中有5个专业同时也?007届失业最多的专业Q计机U学与技术、英语、国际经与贸易、法学、工商管理。调控这些连l造成较大׃量的专业招生l构Qƈ适当调整此类专业的在校学生结构，可以较快地改善M׃状况。另一斚wQ河北省2008届高职高专毕业生毕业半年后失业量最多的10个专业占了高职高专失业量?3.1%?br />大学毕业生最不愿d?br />从就业城市类型期待来看，沛_?008届大学毕业生对就业地域的期望不是完全合理的。河北省2008届大学毕业生最愿意ȝ是副省城市和直辖市Q最不愿意去的是区县?br />据悉Q该报告ZҎ北省2008届大学毕业生半年后的调查研究Q对2008届河北省大学毕业生的׃向、就业与收入、工作能力、求职、就业与教育公^、自d业、读研与留学、大学毕业生的满意度{做Z全面的研I分析。调查覆盖了沛_省本U院校与高职高专院校中的101所Q本?008届大学毕业生9223人；在河北省׃?008届大学毕业生3437人；生源地在沛_省的2008届大学毕业生7806人。虽然抽栯盖了本省大部分的各类学校Q但主要指标hl计U学的M代表性，不排除个别指标上可能有一定代表性误?
]]>
先说׃形势, ?008q?月䆾往? 基本上投? 投一千䆾才可能有一份回? 在走访了学生之后(臛_三家培训机构), UL表示׃? 每班׃者寥?低达10%), 而不是招生广告上鼓吹的找不到工作者寥? 今年春节q后, 形势q一步恶? 以我所在公ؓ? 一个技术维护职位每天都?0人左x面试, 可见竞争之激? 不单无ITl验者难׃, 从周围朋友同学的情况来看(q_5q?l验), 普遍也存在离职后再就业难的问? q说明什么问题呢? 那就是职位太? 太少. 是学生不努力? 不是, 怿大部分还是很努力? 那么危机何时l束? 我不知道, 今年肯定是结束不了的.
怿q有很多? 希望先学好技? 我个得在目前的金融危机Ş势下, 看教学视频学习是最好的方式, 既不耽误现有工作, 又能学到技? 毕竟参加培训Ҏ不能保证׃, 目的也只能是可能学好技术而已. 如果您是Z׃d加培? h立即停止q种费父母血汗钱的行?
现在参加培训能得C? 可能到手的好技?需要打好基外加天天熬夜l习), 一份培训毕业证? 一份好工作(l对没有!). 付出的是什? 1万左右的现金, 4 ~ 5个月的时? 外加生活费和满腔的希? 也许q去和将来是参加培训然后׃的好Z, 现在l对不是.
]]>