Can I set up profiles like jhat or jmap to take snapshots at regular intervals or whenever exception is detected

Question

So basically in our case the server goes down mysteriously and we often restart it and it starts to work fine. Till now we haven't been able to establish a pattern. Looking at thread dump did help but we want to analyse memory usage too. Can these tools be set up to run at regular intervals (so they keep saving snapshots at regular intervals) or whenever it detects an exception or crash

Answer 1

It won't produce a complete dump, but jstat can be run continuously to provide sumamry statistics of memory over time at regular intervals:

> jstat -gccause -t <JVMID> 60s

for instance, will produce memory pool and garbage collection statistics every minute until you kill it with Ctrl-C.

jstat can do a lot more than memory and garbage collection. See the jstat manpage for more information:

http://docs.oracle.com/javase/6/docs/technotes/tools/share/jstat.html

Answer 2

run jmap in a cron?

Another option is to attach jdb to the process. It will stop on uncaught exception and you can take a heap dump using jmap in that state. Unfortunately jdb itself doesn't support taking a heap dump.