Master JVM Performance: Essential jps, jstack, jmap, jstat & hprof Tools

Background

In enterprise Java development and maintenance, developers often encounter problems such as OutOfMemoryError, memory leaks, thread deadlocks, lock contention, and high CPU usage. Understanding and solving these issues is essential for advancing as a Java programmer.

jps

jps outputs information about JVM processes. Syntax: jps [options] [hostid] Common options:

-q  Do not output class name, JAR name, or main arguments
-m  Output arguments passed to the main method
-l  Output the full package name of the main class or JAR
-v  Output arguments passed to the JVM

Example:

root@ubuntu:/# jps -m -l
2458 org.artifactory.standalone.main.Main /usr/local/artifactory-2.2.5/etc/jetty.xml
29920 com.sun.tools.hat.Main -port 9998 /tmp/dump.dat
...

jstack

jstack displays thread stack traces for a Java process. Syntax:

jstack [option] pid
jstack [option] executable core
jstack [option] [server-id@]remote-hostname-or-ip

Key options:

-l  Long listings, prints additional lock information (useful for deadlocks)
-m  Mixed mode, includes native stack frames

Example to find the most CPU‑intensive thread:

# ps -ef | grep mrf-center | grep -v grep
root 21711 1 1 14:47 pts/3 00:02:10 java -jar mrf-center.jar
# top -Hp 21711   (identify thread ID 21742)
# printf "%x
" 21742
54ee
# jstack 21711 | grep 54ee
"PollIntervalRetrySchedulerThread" prio=10 tid=0x00007f950043e000 nid=0x54ee in Object.wait() [0x00007f94c6eda000]

The identified thread is waiting in PollIntervalRetrySchedulerThread ’s Object.wait() call.

jmap and jhat

jmap exports heap memory information; jhat analyzes the exported heap dump.

jmap [option] pid
jmap -heap pid
jmap -histo[:live] pid
jmap -dump:format=b,file=dumpFileName pid

Example of heap summary:

jmap -heap 21711
Attaching to process ID 21711, please wait...
Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 2067791872 (1972.0MB)
...

To analyze a dump:

# jmap -dump:format=b,file=/tmp/dump.dat 21711
Dumping heap to /tmp/dump.dat ...
Heap dump file created
# jhat -port 9998 /tmp/dump.dat
Started HTTP server on port 9998

jstat

jstat monitors JVM statistics such as memory usage and garbage collection.

jstat [ generalOption | outputOptions vmid [interval[s|ms] [count]] ]

Example showing GC information:

# jstat -gc 21711 250 4
S0C S1C S0U S1U EC EU OC OU PC PU YGC YGCT FGC FGCT GCT
192.0 192.0 64.0 0.0 6144.0 1854.9 32000.0 4111.6 55296.0 25472.7 702 0.431 3 0.218 0.649
...

Column meanings:

S0C, S1C – Survivor space capacities
S0U, S1U – Survivor space usage
EC, EU – Eden space capacity and usage
OC, OU – Old generation capacity and usage
PC, PU – Permanent generation capacity and usage
YGC, YGCT – Young GC count and time
FGC, FGCT – Full GC count and time
GCT – Total GC time

hprof

hprof provides CPU usage and heap profiling.

java -agentlib:hprof[=options] ToBeProfiledClass
java -Xrunprof[:options] ToBeProfiledClass
javac -J-agentlib:hprof[=options] ToBeProfiledClass

Key options include:

heap=dump|sites|all   Heap profiling
cpu=samples|times    CPU usage profiling
monitor=y|n          Monitor contention
format=a|b           Output format (text or binary)
file=<file>          Output file name
interval=<ms>        Sampling interval in ms
depth=<size>        Stack trace depth

Example of CPU sampling profiling:

java -agentlib:hprof=cpu=samples,interval=20,depth=3 Hello

Example of CPU times profiling: javac -J-agentlib:hprof=cpu=times Hello.java Example of heap allocation profiling: javac -J-agentlib:hprof=heap=sites Hello.java Example of heap dump generation:

javac -J-agentlib:hprof=heap=dump Hello.java