tomcat 6 hangs after a few hours

Question

We have an application on tomcat using SQL server on top on Windows server 2007 web (IIS disabled) it works smoothly for a few hours but then it suddenly stops answering requests. Log aren't too informative. We've seen an NullPointer exception on a certain JSP, but the syetem only hanged 30 hours after that. We see manly exceptions on Tomcat lo4j log...but nothing appears related. THe application itself it partly black box

Answer 1

Aside from application specific stuff (what resources is the application waiting on? is it holding references to them?) and turning up the logging level, try:

run tomcat with flags to output GC activity:

java -verbose:gc

Here's a good reference on gc tuning, but to check for a hang you probably just want to see if it runs into a memory error.

You can also use jstack to check the status of your threads, see what's hanging:

jstack PID