On Feb 24, 2009, at 3:57 PM, Juha Laiho wrote:
So, looks like I'm late to the party, but will crash in nonetheless.
Sam Hokin wrote:
Christopher Schultz wrote:
On 2/19/2009 6:23 PM, Sam Hokin wrote:
The problem, which spontaneously appeared a few days before
Christmas on
this one server, is that the initial request of a JSP or servlet
takes
AGES to respond, usually exceeding several minutes.
Well, I have used a number of diagnostics, like jconsole, jstat and
jhat, but haven't been able to glean anything informative from them
about my issue. I've run the -Xloggc JVM option, and watched it
garbage
collect, again not informing me of anything. Yes, if I could
figure out
what the JVM is actually DOING doing the long wait, I'd hopefully be
able to deal with it, but I honestly haven't been able to figure
out how
to do that. What do you suggest?
I'll cast my hat into the ring: I suspect you're loading a
resource that
wants to looking an external resource (like an XML file with a
remote
DTD/Schema and validation is on in the parser) and the DNS is
tripping
you up.
No, there are no external references in my Java package. It's all
just
local class files.
Still it sounds like a network (DNS) issue, but it does not pay to
just
argue, more information is needed.
One tool that I haven't yet seen suggested is 'strace', the Linux
system
call tracer. This will show all the calls your application makes to
the
operating system. As you say the application is mostly idle during the
delay, it is, in one way or another, waiting for some OS service to
complete. 'strace' should provide you with timestamped information on
what OS services were called, with which arguments, and how long did
it take for them to return with results. 'strace' will leave you with
a huge file (or a set of huge files, depending on the options you
use),
and going through them will take some time - but you'll most likely
also find what causes the delay.
If you decide to go this way, trim down your application to the
minimum
where you can still see the delay; with this you hopefully can get
at least some reduction to the amount of log data written. Even
though it
is possible to temporarily attach strace to a running process (like
the Tomcat at the moment when it is hung), I'd recommend starting the
tomcat under truss (with -f or -ff to make it also trace new processes
created), because this way it is easier to trace back the file
descriptor
numbers accessed.
--
..Juha
It could be other network issue, like having IP6 enabled on the
machine connected to an IP4 network, or an inefficient routing of
network traffic for that particular machine. Sounds like it is timing
out on some network task.
János
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