Wen Cheng wrote:
So, the only explaination for the peak is, every half an hour, the server does something else, this "something" is consuming, using a lot of system resources.
I can't think of anything that the server would do every 30 minutes that would result in this.
Try enabling the access log valve on the server and get the access logs which will show you what URLs are being requested.
The access log is already opened.
I wrote programs to analysis the log, the result shows that the http requests are smoonth, no strange requests when the "peak" happens, nealy 70 requests every seconds.
And all the requests is the same kind —— the clients report to the server "hey, I am still alive! " . So the consuming of every request is nearly the same.
If jboss doesn't do that half-an-hour-regular job, I will looking for other causes.