“hsperfdata_”-files in /tmp (or $TMPDIR) – jstat

The “hsperfdata_”-files are part of the java performance monitoring since version 1.4.2.
A general FAQ can be found here. A part of this performance monitoring aspect is “jstat”. It’s a Java SE bundled command-line JVM statistics monitoring tool.

To see what type of statistics you can choose from:
jstat -options

For example, to see a summary of garbage of collection statistics:
jstat -gcutil

[root@pingu:/tmp]# ls /tmp/hsperfdata_sandbox/
4828 4843 5024 5081
[root@pingu:/tmp]# jstat -gcutil 4828
S0 S1 E O P YGC YGCT FGC FGCT GCT 0.00 98.11 74.98 38.82 94.05 23 1.033 1 0.181 1.213

A syntax explanation on howto use “jstat” can be found here.