Troubleshooting Java HotSpot VM

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. |
Troubleshooting
Java HotSpot VM
Poonam Parhar
Consulting Member of Technical Staff
JVM Sustaining Engineering, Oracle
Sept 22, 2016

Safe Harbor Statement
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information purposes only, and may not be incorporated into any contract. It is not a
commitment to deliver any material, code, or functionality, and should not be relied upon
in making purchasing decisions. The development, release, and timing of any features or
functionality described for Oracle’s products remains at the sole discretion of Oracle.
4

Troubleshooting
• Systematic approach to solving problems
• Troubleshooting is partly science and partly an art
• Curiosity, focus, attention to the details, persistence,
patience and experience play a great role
• Good troubleshooting tools are your friends
• Three simple steps:
1. Understand the problem/error
2. Collect the required diagnostic data
3. Analyze the collected data
5

Troubleshooting
Java HotSpot Virtual Machine
6

HotSpot JVM issues
• OutOfMemory errors / Memory leaks
• Latencies or Pauses
• JVM Hangs / Stuck threads
• High CPU usage
• Application Crashes
• Java Exceptions
7

Agenda
Look at the HotSpot JVM issues one by one
How to approach them
Troubleshooting and Debugging tools
Best Practices for Troubleshooting HotSpot JVM
Q&A
1
2
3
4
8
5

Memory Problems
9

Copyright © 2016, Oracle and/or its affiliates. All rights reserved. | 10
Memory Problems: understand
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOfRange(Unknown Source) at
java.lang.String.<init>(Unknown Source) at
java.io.BufferedReader.readLine(Unknown Source) at
java.io.BufferedReader.readLine(Unknown Source) at
org.girs.TopicParser.dump(TopicParser.java:23) at
org.girs.TopicParser.main(TopicParser.java:59)
#
# A fatal error has been detected by the Java Runtime Environment:
#
# java.lang.OutOfMemoryError: requested 32756 bytes for
ChunkPool::allocate. Out of swap space?
#
# Internal Error (allocation.cpp:166), pid=2290, tid=27
# Error: ChunkPool::allocate
#

OutOfMemoryError: Java Heap Space
• Ensure that footprint is not larger than the maximum specified heap size
• Look at GC logs to determine stable footprint
688995.775: [Full GC [PSYoungGen: 46400K->0K(471552K)] [ParOldGen: 1002121K-
>304673K(1036288K)] 1048521K->304673K(1507840K) [PSPermGen: 253230K-
>253230K(1048576K)], 0.3402350 secs] [Times: user=1.48 sys=0.00, real=0.34 secs]
• Increase the heap size using –Xmx JVM option
May indicate that there is a memory leak
Watch if live-set is increasing over time
11

Java Memory Leak
• Java Flight Recorder
– with Heap Statistics Enabled
• Heap Dumps come to rescue
– jcmd <process id/main class> GC.heap_dump filename=Myheapdump
– jmap -dump:format=b,file=snapshot.jmap pid
– JConsole utility, using Mbean HotSpotDiagnostic
• -XX:+HeapDumpOnOutOfMemoryError
• Heap Histogram
– -XX:+PrintClassHistogram and Control+Break
– jcmd <process id/main class> GC.class_histogram filename=Myheaphistogram
– jmap -histo pid
– jmap -histo <java> core_file
• Monitor Objects Pending Finalization
– JConsole
– jmap – finalizerinfo
12
collect diagnostic data

Java Memory Leak
• Flight Recordings with Java Mission Control
• Heap dumps can be analyzed using
– Jhat
– Java VisualVM
– Eclipse MAT
– JOverflow JMC plugin
13
analyze data

OutOfMemoryError: PermGen Space (*removed in JDK8*)
• Appropriately configure the PermGen Size with –XX:PermSize=n and –
XX:MaxPermSize=m
• Make sure that classes are getting unloaded
-XX:+TraceClassUnloading –XX:+TraceClassLoading
• -Xnoclassgc
• CMS: enable class unloading with
• –XX:+CMSClassUnloadingEnabled
• Monitor using Java Mission Control or JConsole
• jmap and SA tool to examine PermGen
• Heap Dumps help here too
16

$ jmap -permstat 29620
Attaching to process ID 29620, please wait...
Debugger attached successfully.
Client compiler detected.
JVM version is 24.85-b06
12674 intern Strings occupying 1082616 bytes.
finding class loader instances ..
done.
computing per loader stat ..done.
please wait.. computing liveness.........................................done.
class_loader classes bytes parent_loader alive? type
<bootstrap> 1846 5321080 null live <internal>
0xd0bf3828 0 0 null live sun/misc/Launcher$ExtClassLoader@0xd8c98c78
0xd0d2f370 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0c99280 1 1440 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0b71d90 0 0 0xd0b5b9c0 live java/util/ResourceBundle$RBClassLoader@0xd8d042e8
0xd0d2f4c0 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0b5bf98 1 920 0xd0b5bf38 dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0b5bf38 6 11832 0xd0b5b9c0 dead sun/reflect/misc/MethodUtil@0xd8e8e560
0xd0d2f3a8 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0b5b9c0 317 1397448 0xd0bf3828 live sun/misc/Launcher$AppClassLoader@0xd8cb83d8
0xd0d2f3e0 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0ec3968 1 1440 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0e0a248 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0d2f4f8 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
0xd0e0a280 1 904 null dead sun/reflect/DelegatingClassLoader@0xd8c22f50
total = 22 2186 6746816 N/A alive=4, dead=18 N/A
jmap -permstat

java -classpath %JAVA_HOME%libsa-jdi.jar sun.jvm.hotspot.tools.PermStat 1367
Client compiler detected.
JVM version is 24.0-b56
10713 intern Strings occupying 802608 bytes.
finding class loader instances ..
done.
please wait.. computing
liveness..............................................done.
0x23f7b398 3 28016 0x23f762e0 live sun/misc/Launcher$AppClassLoader@0x38a0e9c0
0x23f762e0 0 0 null live sun/misc/Launcher$ExtClassLoader@0x389eb420
SA Tool for PermGen Inspection

Metaspace (since JDK 8)
• Java Classes metadata is stored in Metaspace
• Increase metaspace size with MaxMetaspaceSize
2. java.lang.OutOfMemoryError: Compressed class space
• CompressedClassSpaceSize
• Default size is 1G
1. OutOfMemoryError: Metaspace
• jmap -clstats
• jcmd GC.class_stats
• -XX:+PrintGCDetails
• NMT, JConsole, VisualVM
Diagnostic data and Tools

OutOfMemoryError: Native heap
• 32-bit JVM, running out of address space
• Strange when you get this error with 64bit JVM
• Failure with CompressedOops
– Unscaled Compressed Oops: Java heap placed below 4GB address space
– Zero Based Compressed Oops: Java heap placed below 32GB address space
• -XX:HeapBaseMinAddress=n
• https://blogs.oracle.com/poonam/entry/running_on_a_64bit_platform
21

#
# There is insufficient memory for the Java Runtime Environment to continue.
# Native memory allocation (malloc) failed to allocate 5408 bytes for CodeCache: no room for vtable chunks
# Possible reasons:
# The system is out of physical RAM or swap space
# In 32 bit mode, the process size limit was hit
# Possible solutions:
# Reduce memory load on the system
# Increase physical memory or swap space
# Check if swap backing store is full
# Use 64 bit Java on a 64 bit OS
# Decrease Java heap size (-Xmx/-Xms)
# Decrease number of Java threads
# Decrease Java thread stack sizes (-Xss)
# Set larger code cache with -XX:ReservedCodeCacheSize=
# This output file may be truncated or incomplete.
#
# Out of Memory Error (vtableStubs.cpp:63), pid=23796, tid=246
# Java VM: Java HotSpot(TM) 64-Bit Server VM (24.80-b11 mixed mode solaris-sparc compressed oops)
#
Current thread (0x000000010dccb130): JavaThread "[ACTIVE] ExecuteThread: '190' for queue: 'weblogic.kernel.Default (self-tuning)'"
daemon [_thread_in_vm, id=246, stack(0xffffffff47e00000,0xffffffff47e80000)]
Stack: [0xffffffff47e00000,0xffffffff47e80000], sp=0xffffffff47e74820, free space=466k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0xcc7b44] void VMError::report_and_die()+0x774
V [libjvm.so+0x62fc58] void report_vm_out_of_memory(const char*,int,unsigned long,const char*)+0x88
V [libjvm.so+0xcd72f8] void*VtableStub::operator new(unsigned long,int)+0xb8
V [libjvm.so+0xcd8844] VtableStub*VtableStubs::create_itable_stub(int)+0x74
V [libjvm.so+0xcd764c] unsigned char*VtableStubs::create_stub(bool,int,methodOopDesc*)+0x124
V [libjvm.so+0x2fbc90] void CompiledIC::set_to_megamorphic(CallInfo*,Bytecodes::Code,Thread*)+0x50
V [libjvm.so+0x2fe4d4] methodHandle SharedRuntime::handle_ic_miss_helper(JavaThread*,Thread*)+0x3f4
V [libjvm.so+0xbb98e8] unsigned char*SharedRuntime::handle_wrong_method_ic_miss(JavaThread*)+0x30
………

hsdb> universe
Heap Parameters:
ParallelScavengeHeap [ PSYoungGen [
eden = [0x0000000700000000,0x00000007007ae238,0x000000070c000000] ,
from = [0x000000070e0000 00,0x000000070e000000,0x0000000710000000] ,
to = [0x000000070c000000,0x000000070c000000,0x000000070e000000] ]
PSOldGen [ [0x0000000500400000,0x0000000500400000,0x0000000520200000] ]
PSPermGen [ [0x00000004fb200000,0x00000004fb483380,0x00000004fc800000] ]
bash-4.1$ pmap 6049
0000000000400000 4K r-x-- /java/bin/amd64/java
0000000000410000 4K rw--- /java/bin/amd64/java
0000000000411000 2288K rw--- [ heap ]
00000004FB200000 22528K rw--- [ anon ]  Java Heap starts here
0000000500400000 522240K rw--- [ anon ]
0000000700000000 262144K rw--- [ anon ]

#
# Possible reasons:
# The system is out of physical RAM or swap space
# The process is running with CompressedOops enabled, and the Java Heap may be blocking the growth of the native heap
# Possible solutions:
# Reduce memory load on the system
# Increase physical memory or swap space
# Check if swap backing store is full
# Decrease Java heap size (-Xmx/-Xms)
# Decrease number of Java threads
# Decrease Java thread stack sizes (-Xss)
# Set larger code cache with -XX:ReservedCodeCacheSize=
# JVM is running with Unscaled Compressed Oops mode in which the Java heap is
# placed in the first 4GB address space. The Java Heap base address is the
# maximum limit for the native heap growth. Please use -XX:HeapBaseMinAddress
# to set the Java Heap base and to place the Java Heap above 4GB virtual address
# This output file may be truncated or incomplete.
Improved native memory error message
Error message improved
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/2f77f01444dd

Native Heap Leak
• Native Memory Tracker (NMT)
– -XX:NativeMemoryTracking=off, summary, detail
– -XX:+UnlockDiagnosticVMOptions -XX:+PrintNMTStatistics
– jcmd <pid> VM.native_memory
• Platform specific debugging tools
– dbx, libumem, valgrind, purify
25
Tools

d:tests>jcmd 90172 VM.native_memory
90172:
Native Memory Tracking:
Total: reserved=3431296KB, committed=2132244KB
- Java Heap (reserved=2017280KB, committed=2017280KB)
(mmap: reserved=2017280KB, committed=2017280KB)
- Class (reserved=1062088KB, committed=10184KB)
(classes #411)
(malloc=5320KB #190)
- Thread (reserved=15423KB, committed=15423KB)
(thread #16)
(stack: reserved=15360KB, committed=15360KB)
(malloc=45KB #81)
(arena=18KB #30)
- Code (reserved=249658KB, committed=2594KB)
(malloc=58KB #348)
- GC (reserved=79628KB, committed=79544KB)
(malloc=5772KB #118)
- Compiler (reserved=138KB, committed=138KB)
(malloc=8KB #41)
(arena=131KB #3)
- Internal (reserved=5380KB, committed=5380KB)
(malloc=5316KB #1357)
- Symbol (reserved=1367KB, committed=1367KB)
(malloc=911KB #112)
(arena=456KB #1)
- Native Memory Tracking (reserved=118KB, committed=118KB)
(malloc=66KB #1040)
(tracking overhead=52KB)
- Arena Chunk (reserved=217KB, committed=217KB)
(malloc=217KB)

Latencies

Latencies
• Long GC Pauses
• Safepoint operations
– Stop-the-world pauses to execute VM operations for its internal maintenance
– e.g. Deoptimization, RevokeBias, JFRCheckpoint
• Other JVM tasks
– E.g. CodeCache cleaning
• Debug operations e.g dumping stack trace
• I/O
28
understand causes

Latencies
• Java Flight Recording – events taking long time
• Collect GC logs
• Collect stack traces including native frames
• -XX:+PrintGCApplicationStoppedTime
• -XX:+PrintSafepointStatistics –XX:PrintSafepointStatisticsCount=1
29

JFR - events with long durations
30

vmop [threads: total initially_running wait_to_block] [time: spin block sync cleanup vmop] page_trap_count
2.743: RedefineClasses [ 6 0 0 ] [ 0 0 0 0 4 ] 0
2.815: JFRCheckpoint [ 7 0 0 ] [ 0 0 0 0 0 ] 0
2.816: PrintThreads [ 7 0 0 ] [ 0 0 0 0 0 ] 0
2.816: PrintJNI [ 7 0 0 ] [ 0 0 0 0 0 ] 0
2.817: FindDeadlocks [ 7 0 0 ] [ 0 0 0 0 0 ] 0
3.817: no vm operation [ 11 0 1 ] [ 0 5 5 0 0 ] 0
7.174: EnableBiasedLocking [ 11 0 0 ] [ 0 0 0 0 0 ] 0
102.319: PrintThreads [ 11 0 2 ] [ 0 0 0 0 0 ] 0
102.322: PrintJNI [ 11 0 0 ] [ 0 0 0 0 0 ] 0
Safepoints

GC Pauses
• Collect GC logs with -XX:+PrintGCDetails -XX:+PrintHeapAtGC -
XX:+PrintGCTimeStamps -XX:+PrintGCDateStamps and -
XX:+PrintGCApplicationStoppedTime
• Use GCHisto, VisualGC, gclogviewer or other GC logs analysis tools
• Monitor the overall health of the system using OS tools like vmstat, iostat,
netstat and mpstat etc. on Solaris and Linux platforms, and tools like Process
Monitor and Task Manager on the Windows operating system
• CMS collector, add option -XX:PrintFLSStatistics=2
• Inspect GC logs to see any signs of fragmentation
• Monitor if the specified heap size is enough to contain the footprint of the
application.
32
how to approach

GC Pauses
166687.013: [Full GC [PSYoungGen: 126501K->0K(922048K)] [PSOldGen:
2063794K->1598637K(2097152K)] 2190295K->1598637K(3019200K)
[PSPermGen: 165840K->164249K(166016K)], 6.8204928 secs] [Times: user=6.80
sys=0.02, real=6.81 secs]
166699.015: [Full GC [PSYoungGen: 125518K->0K(922048K)] [PSOldGen:
1763798K->1583621K(2097152K)] 1889316K->1583621K(3019200K)
[PSPermGen: 165868K->164849K(166016K)], 4.8204928 secs] [Times: user=4.80
sys=0.02, real=4.81 secs]
33
insufficient memory spaces

(to-space exhausted), 2.8504662 secs]
[Parallel Time: 2778.5 ms, GC Workers: 16]
[GC Worker Start (ms): Min: 122158804.8, Avg: 122158805.1, Max: 122158805.3, Diff: 0.5]
[Ext Root Scanning (ms): Min: 869.1, Avg: 896.0, Max: 952.5, Diff: 83.4, Sum: 14335.3]
[Update RS (ms): Min: 18.4, Avg: 27.0, Max: 34.6, Diff: 16.2, Sum: 431.5]
[Processed Buffers: Min: 18, Avg: 33.0, Max: 48, Diff: 30, Sum: 528]
[Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3]
[Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Object Copy (ms): Min: 1805.5, Avg: 1854.5, Max: 1878.0, Diff: 72.5, Sum: 29671.2]
[Termination (ms): Min: 0.0, Avg: 0.2, Max: 0.3, Diff: 0.3, Sum: 3.0]
[GC Worker Other (ms): Min: 0.0, Avg: 0.2, Max: 0.4, Diff: 0.3, Sum: 2.8]
[GC Worker Total (ms): Min: 2777.4, Avg: 2777.8, Max: 2778.0, Diff: 0.6, Sum: 44444.1]
[GC Worker End (ms): Min: 122161582.7, Avg: 122161582.8, Max: 122161583.0, Diff: 0.3]
[Code Root Fixup: 8.4 ms]
[Code Root Migration: 0.0 ms]
[Clear CT: 0.5 ms]
[Other: 63.0 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 1.1 ms]
[Ref Enq: 0.0 ms]
[Free CSet: 0.4 ms]
[Eden: 64.0M(792.0M)->0.0B(920.0M) Survivors: 128.0M->0.0B Heap: 18.1G(18.1G)->18.1G(18.1G)]
[Times: user=25.31 sys=1.01, real=2.85 secs]
GC log

GC Pauses
164638.058: [Full GC (System) [PSYoungGen: 22789K->0K(992448K)] [PSOldGen:
1645508K->1666990K(2097152K)] 1668298K->1666990K(3089600K) [PSPermGen:
164914K->164914K(166720K)], 5.7499132 secs] [Times: user=5.69 sys=0.06, real=5.75
secs]
• -Dsun.rmi.dgc.server.gcInterval=n -Dsun.rmi.dgc.client.gcInterval=n
• kill -3 with -XX:+PrintClassHistogram
• -XX:+DisableExplicitGC
36
explicit GCs

GC Pauses - High ‘sys’ time
2013-07-17T03:58:06.601-0700: 51522.120: [GC: 2696384K->449344K(2696384K),
29.4779282 secs] 4557003K->2326821K(12133568K) ,29.4795222 secs] [Times:
user=1.56 sys=26.35, real=29.48 secs]
37
Corresponding 'vmstat' output at 03:58:
kthr memory page disk faults cpu r b w swap free re mf pi po fr de sr s0 s1 s2 s3 in sy cs us sy id
20130717_035806 0 0 0 77611960 94847600 55 266 0 0 0 0 0 0 0 0 0 3041 2644 2431 44 8 48
20130717_035815 0 0 0 76968296 94828816 79 324 0 18 18 0 0 0 0 1 0 3009 3642 2519 59 13 28
20130717_035831 1 0 0 77316456 94816000 389 2848 0 7 7 0 0 0 0 2 0 40062 78231 61451 42 6
53

GC Pauses - low ‘user’, low ‘sys’ time
• GC threads stuck waiting for Kernel I/O
• File System flushes
• FS flushing may be invoked due to log files rotation
38

Hung Processes or Stuck Threads

Hung Processes or Stuck Threads
• Check if Java level deadlock – Ctrl+ or Ctrl+Break
• Stack trace with jstack
– jstack –m to get the native frames
– jstack –l to get concurrent locks information
– jstack –F
• Check what VMThread is doing
– SafepointSynchronize::begin
– Performing a VM Operation
• Network or I/O operations
• Collect Core file to investigate the threads stuck in native code (JNI or JVM)
• It may appear that the thread(s) are stuck in a particular java method but that method may be getting
invoked repeatedly from a loop
• Thread may appear to be stuck in a Java method but may be doing something else at the native level e.g.
threads stuck in looking for space in CodeCache.
40

----------------- 11628 -----------------
0x0000003fe900af59 ????????
0x00002ac4ae68f258 _ZN7Monitor5ILockEP6Thread + 0x1b8
0x00002ac4ae68f48f _ZN7Monitor28lock_without_safepoint_checkEv + 0x2f
0x00002ac4ae2ce713 _ZN9CodeCache18largest_free_blockEv + 0x33
0x00002ac4ae2f97a5 _ZN13CompileBroker14compile_methodE12methodHandleiiS0_iPKcP6Th
read + 0x3b5
0x00002ac4ae1443cd _ZN23AdvancedThresholdPolicy14submit_compileE12methodHandlei9C
ompLevelP10JavaThread + 0x8d
0x00002ac4ae77fab0 _ZN21SimpleThresholdPolicy5eventE12methodHandleS0_ii9CompLevel
P7nmethodP10Java Thread + 0x250
0x00002ac4ae4a39d7 _ZN18InterpreterRuntime32frequency_counter_overflow_innerEP10J
avaThreadPh + 0x157
0x00002ac4ae4a79d6 _ZN18InterpreterRuntime26frequency_counter_overflowEP10JavaThr
eadPh + 0x16
0x00002aaaab1a347a * javax.management.MBeanInfo.getClassName() bci:0
line:289 (Interpreted frame)
Example: native stack trace

java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for < 0x00000006e95c8088 > (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
at
java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:834
)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:867)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1197)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:214)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:290)
at oracle.jbo.mom.DefinitionContext.lock(DefinitionContext.java:550)
at oracle.jbo.mom.DefinitionManager.getSiteLock(DefinitionManager.java:4710)
at oracle.jbo.mom.DefinitionManager.lockDefinitionContext(DefinitionManager.java:4667)
at oracle.jbo.mom.DefinitionContextAgeable.cleanNullRefs(DefinitionContextAgeable.java:253)
Concurrent Locks

Concurrent locks information
Thread 9409: (state = IN_NATIVE)
- java.net.SocketInputStream.socketRead0(java.io.FileDescriptor, byte[], int, int, int) @bci=0
- java.net.SocketInputStream.read(byte[], int, int, int) @bci=87, line=152 (Compiled frame)
- java.net.SocketInputStream.read(byte[], int, int) @bci=11, line=122 (Compiled frame)
- oracle.net.nt.MetricsEnabledInputStream.read(byte[], int, int) @bci=38, line=730 (Compiled frame)
- oracle.net.ns.Packet.receive() @bci=180, line=302 (Compiled frame)
- oracle.net.ns.DataPacket.receive() @bci=1, line=108 (Compiled frame)
- oracle.net.ns.NetInputStream.getNextPacket() @bci=48, line=325 (Compiled frame)
- oracle.net.ns.NetInputStream.read(byte[], int, int) @bci=33, line=269 (Compiled frame)
- oracle.net.ns.NetInputStream.read(byte[]) @bci=5, line=191 (Compiled frame)
………
- weblogic.timers.internal.TimerImpl.run() @bci=91, line=284 (Compiled frame)
- weblogic.work.SelfTuningWorkManagerImpl$WorkAdapterImpl.run() @bci=4, line=550 (Compiled frame)
- weblogic.work.ExecuteThread.execute(java.lang.Runnable) @bci=34, line=263 (Compiled frame)
- weblogic.work.ExecuteThread.run() @bci=42, line=221 (Interpreted frame)
Locked ownable synchronizers:
- <0x00000006e95c8088>, (a java/util/concurrent/locks/ReentrantLock$NonfairSync)
43
jstack -l

High CPU Usage

High CPU Usage
• Java Flight Recordings
• Find the thread that is responsible consuming CPU cycles
– prstat –L
– ps, top (shift H)
• Get the Thread ID from the above output
• Get stack trace with jstack
• Find the stack trace of the thread consuming CPU
45

prstat -L
bash-3.2$ prstat -L
PID USERNAME SIZE RSS STATE PRI NICE TIME CPU PROCESS/LWPID
704 pobajaj 505M 36M cpu18 0 0 0:01:50 3.1% java/48
21592 root 71M 42M sleep 60 0 16:26:30 1.7% obndmpd/1
9990 root 2016K 1672K sleep 60 0 0:32:23 0.5% find/1
21590 root 45M 15M sleep 59 0 0:38:41 0.0% obndmpd/1
725 pobajaj 4264K 3912K cpu5 39 0 0:00:00 0.0% prstat/1
704 pobajaj 505M 36M sleep 45 0 0:00:00 0.0% java/46
46

bash-3.2$ jstack 704
2016-08-14 07:43:15
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.60-b23 mixed mode):
"Attach Listener" #24 daemon prio=9 os_prio=64 tid=0x0000000100428000 nid=0x31 waiting on condition
[0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"DestroyJavaVM" #23 prio=5 os_prio=64 tid=0x000000010010f000 nid=0x2 waiting on condition
[0x0000000000000000]
"Thread2" #22 prio=5 os_prio=64 tid=0x000000010045c000 nid=0x30 runnable [0xfffffffe52aff000]
at Thread2.run(TestCPU.java:25)
at java.lang.Thread.run(Thread.java:745)
"Service Thread" #20 daemon prio=9 os_prio=64 tid=0x0000000100410000 nid=0x2d runnable
[0x0000000000000000]
jstack output

Application Crashes
48

Application Crashes
• Crash could be in:
– Native Code
– Compiled Code or Hotspot Compiler thread
– VM Thread
– GC Threads
• First thing to look at is the hs_err log file
49
understand cause
#
#
# SIGSEGV (0xb) at pc=0x00007f438b2c86ad, pid=8359, tid=139928047384320
#
# JRE version: Java(TM) SE Runtime Environment (8.0_40-b19) (build 1.8.0_40-ea-b19)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.40-b23 mixed mode linux-amd64 compressed oops)
# Problematic frame:
# V [libjvm.so+0x5b86ad] G1ParScanThreadState::copy_to_survivor_space(oopDesc*)+0x3d
#
Current thread (0x00036960): JavaThread "main" [_thread_in_vm, id=2896]
Stack: [0x00040000,0x00080000), sp=0x0007f9f8, free space=254k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [jvm.dll+0x83d77]
C [TestApp.dll+0x1047]
j Test.methodA()V+0
j Test.main([Ljava/lang/String;)V+0
v ~StubRoutines::call_stub
V [jvm.dll+0x80f13]

Crashes
• hs_err log file
• Core files
• Java Flight Recording (DumpJFR)
• GC Logs
• -XX:+VerifyBeforeGC –XX:+VerifyAfterGC –XX:+VerifyDuringGC –XX:VerifySubset=“subset string”
• Transported core files
– Need to get system libraries from the system where the crash happened
– Tell native debuggers where to look for those libs
• -XX:OnError=“command”
-XX:OnError=“jcmd %p JFR.dump recording=1”
50

Crashes
• -Xcheck:jni
• Remove –Xverify:none or –noverify
• Java Mission Control
• Serviceability Agent
• Native debugging tools: dbx, gdb, windbg etc.
51
Options and Tools
If JVM or JRE library crash
Submit a Bug Report

HotSpot Serviceability Agent
• Debugger for HotSpot JVM
• Platform independent tool, can attach to live Java processes and core files
• Understands the Java Objects and VM Structures
• HSDB, CLHSDB and some other useful utilities
• bin/jhsdb coming up in JDK 9
• java –cp $JAVA_HOME/lib/sa-jdi.jar sun.jvm.hotspot.CLHSDB
hsdb> inspect 0x787696d68
instance of Oop for sun/reflect/GeneratedSerializationConstructorAccessor924844 @ 0x0000000787696d68 @ 0x0000000787696d68 (size = 16)
_mark: 5
_metadata._compressed_klass: InstanceKlass for sun/reflect/GeneratedSerializationConstructorAccessor924844
hsdb> mem 0x787696d68 10
0x0000000787696d68: 0x0000000000000005
0x0000000787696d70: 0x00000000f8d15005
hsdb> universe
Heap Parameters:
ParallelScavengeHeap [ PSYoungGen [ eden = [0x0000000780000000,0x00000007a29ec538,0x00000007a9500000] , from =
[0x00000007a9500000,0x00000007a9500000,0x00000007b4a80000] , to = [0x00000007b4a80000,0x00000007b4a80000,0x00000007c0000000] ] PSOldGen
[ [0x0000000700000000,0x000000077ffb2ae8,0x0000000780000000] ] ]
52

c:Javajdk-9bin>jhsdb
clhsdb command line debugger
hsdb ui debugger
jstack --help to get more information
jmap --help to get more information
jinfo --help to get more information
jsnap --help to get more information
c:Javajdk-9bin>jhsdb jmap --help
<no option> to print same info as Solaris pmap
--heap to print java heap summary
--binaryheap to dump java heap in hprof binary format
--dumpfile name of the dump file
--histo to print histogram of java object heap
--clstats to print class loader statistics
--finalizerinfo to print information on objects awaiting finalization
--exe executable image name
--core path to coredump
--pid pid of process to attach
c:Javajdk-9bin>jhsdb jmap --pid 6472 --clstats
Server compiler detected.
JVM version is 9-ea+124
finding class loader instances ..done.
please wait.. computing liveness.............................................................done.
0x000000008c885848 1 529 null live java/lang/invoke/MethodHandles$LookupHelper$1@0x00000000242d5a00
0x000000008c9c8c68 0 0 null live jdk/internal/loader/ClassLoaders$BootClassLoader@0x00000000242d0048
0x000000008c9c9048 2 2552 0x000000008c9c8c68 live jdk/internal/loader/ClassLoaders$PlatformClassLoader@0x0000000024290150
0x000000008c9c9430 1 972 0x000000008c9c9048 live jdk/internal/loader/ClassLoaders$AppClassLoader@0x000000002428fd18

Working around crashes
• Compiled code or JIT compiler crash
– Try excluding method
– e.g. -XX:CompileCommand=exclude,java/lang/String.indexOf
• GC crash:
– Try alternate GC
54

Java Exceptions

Java Exceptions
• Exception Message
• Classes related exceptions/errors e.g InvalidClassException
• -XX:AbortVMOnException=<exception>
• - XX:AbortVMOnExceptionMessage=<exception message>
• Java Flight Recordings
56

Best Practices for Troubleshooting HotSpot JVM
• Enable Core files
• ulimit -c unlimited
• -XX:+ CreateMinidumpOnCrash
• -XX:+HeapDumpOnOutOfMemoryError
• -XX:GCTimeLimit /-XX:GCHeapFreeLimit with Parallel collector
• Continuous Java Flight Recording
• -XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:FlightRecorderOptions=defaultrecording=true
• Enable GC logging
• Enable JMX for remote monitoring
• -Dcom.sun.management.jmxremote=true
• -Dcom.sun.management.jmxremote.port=n
57

Summary of Tools
• Java Mission Control and Java Flight Recorder
• jcmd
• jmap
• jconsole
• jinfo
• jstack
• Java VisualVM
• Serviceability Agent
• Native debuggers
58

Troubleshooting
Three simple steps:
1. Understand the problem/error
2. Collect the required diagnostic data
3. Analyze the collected data
59

• Troubleshooting Guide
• http://docs.oracle.com/javase/8/docs/tec
hnotes/tools/unix/java.html
• http://openjdk.java.net/groups/hotspot/
docs/Serviceability.html
• https://blogs.oracle.com/poonam
60
Useful Resources

Troubleshooting Java HotSpot VM

Troubleshooting Java HotSpot VM

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