jstat | JavaScript Statistical Library

At least the count (and accumulated time) of garbage collection is exposed via JMX MBeans.

Specifically ManagementFactory.getGarbageCollectorMXBeans() will return a list of GarbageCollectorMXBean objects providing a getCollectionCount() method. You could poll those values and react to them changing.

The command you should use is:

-Xms sets the initial heap size, not the minimum size.

NGCMN and OGCMN denote the minimum capacity of the new generation and the old generation respectively. These numbers are useless most of the time. What you probably wanted to look at is NGC/OGC - the current capacity of the new generation and the old generation.

You've set -Xms3G, and the current heap size is exactly

All these tools (jstack, jmap, jstat...) rely on the communication with the target JVM through /tmp directory.

Apparently Tomcat runs in a different mount namespace, so that its /tmp directory is not the same as /tmp of the current shell. To verify this, run

HotSpot JVM maintains certain Performance Counters that can be read by various serviceability tools.

By default, these performance counters are exported onto the file system under /tmp/hsperfdata_ directory, so that external tools like jstat can read them without direct communication to the JVM. jps tool also looks for these counters to find active JVMs.

JVM does not update the file directly; instead it maps the file into memory and updates the counters in memory. Any such memory update can potentialy cause file I/O. For example, when GC counters are updated during a GC pause, the operating system may decide to flush data to disk, and this in turn may extend the pause. This blog post describes the mentioned effect.

-XX:+PerfDisableSharedMem option forces JVM to use anonymous memory for Performance Counters instead of a mapped file. This helps to avoid random VM pauses caused by spontaneous disk I/O.

With this option, jps, jstat, JConsole and other tools won't be able to find the JVM. However, the performance counters will be still collected. jcmd PerfCounter.print will be able to print the counters anyway.

There is no other negative performance impact of -XX:+PerfDisableSharedMem option. JVM updates counters exactly the same way in both cases; the only difference is whether the counters memory is mapped to a file or not.

Most Java implementations that I worked with use a default Max Heap Size of 25% of system memory and your system probably does not allow overcommit of memory so this might cause this issue. (Source: https://docs.oracle.com/javase/7/docs/technotes/guides/vm/gc-ergonomics.html )

I hope this helps solve the issue:

For jstat you can set -Xmx but you need to prepend -J in front of it like:

jstat -gccapacity $YOUR_JBOSS_PID -J-Xmx10m -J-Xms10m -J-XX:+PrintFlagsFinal

PrintFlagsFinal will show you the effective settings that the JVM will start with, look for: MaxHeapSize for the effective value set by -Xmx or the equivalent: -XX:MaxHeapSize=128m

Source: https://docs.oracle.com/javase/7/docs/technotes/tools/share/jstat.html

Let me know it that helps (and if not, please provide some details like: java -version and uname -a )

See for more info and/or options also: https://chriswhocodes.com/vm-options-explorer.html

Default min memory is not specified and max is 256Mb. It may be problem with not sufficient memory assigned to heap. (It is my suspicion)

Also you could use VisualVM or any other tool that might show more info about what happens there.

S0C/S0U counters are not used with G1 GC.

G1 has no dedicated survivor spaces and no dedicated old/young areas. Any G1 region can serve as Old, Young or Survivor. See this article for details.

S1C/S1U jstat counters represent the total amount of memory occupied by survivor regions; S0C/S0U are always zero.

As for the executable-looking emulator that you can't actually execute, this can happen when the dynamic loader requested by emulator doesn't exist. You can check what kind of file emulator is with the command file emulator, and check what dynamic loader and libraries it needs with ldd emulator (any line showing “not found” is something you need to install). Given the name of the directory and the size of the file, emulator is probably a Linux x86 binary. I suspect you have an amd64 system. If so, you need to install a runtime environment for 32-bit applications; on Ubuntu, you need the ia32-libs package (and perhaps also ia32-libs-gtk). You could also get this error message for a script whose interpreter as indicated in the #! line doesn't exist.

https://superuser.com/questions/178786/what-does-the-asterisk-mean-after-a-filename-when-you-type-ls-l

same question here.