Hello,
I am new to the iSeries, but am old-hat in Java (since JDK1.0a on SunOS 4
circa 1995).
Java performance is very complicated, much like managing LPRs on the
iSeries. You can not use a default configuration for the java runtime and
expect high performance.
Many Java applications are plagued with temporary object creation, which
causes memory fragmentation and ultimately results in the memory controller
in the VM spending many CPU cycles maintaining unnecessary and temporary
links and object pools to keep the first generation pool open for smooth
running.
Next, there is the JIT. The 5i operating system has a JIT option that you
need to enable for the runtime to work well. This JIT is only triggered when
a threshold of re-entries into your code are encountered. This is called
"hotspot" JIT compiling.
http://publib.boulder.ibm.com/infocenter/iseries/v5r3/index.jsp?topic=/rzaha
/selmod.htm
JAVA CLASS(Test) PROP((java.compiler jitc))
That command will run the "Test" class using the JIT compiler. If you are
NOT specifying the use of JITC anywhere in your invocation of the JAVA
command, then you are running in interpreter mode, and your program will be
very slow.
Know also that in the late 90s, IBM was the first to come up with a real
Java compiler (JIKES) that compiled Java down to silicon on Intel/Windows
boxes. They have similar technology built into their VM for the iSeries. You
just need to know how to tweak the runtime properties to manage your memory
and always use the JITC or JITC_DE option.
(JITC_DE): "Machine instructions for a method are generated during the first
call to that method, and saved for use the next time that the program runs.
One copy is also shared for the entire system."
-- Jake
-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Klement
Sent: Monday, February 08, 2010 11:02 AM
To: Midrange Systems Technical Discussion
Subject: Re: Java performance on the i ? Good? bad? OK?
Java's advantage is that it's cross-platform and very well supported.
Being a mainstream language there's a lot of tooling for it, and a lot
of support from major vendors such as Oracle and IBM. There are a lot
of add-in classes for Java that save you having to code things yourself.
[...]
midrange.com
