Calling java from RPG - how to increase performance

Hi chaps,
 
I posted the following on the RPG forum and got a couple of responses, but I
was advised to fire it at you chaps for more info. As a result of the
responses on the RPG forum I'm now using jt400Native.jar instead of
jt400.jar to get a little extra oomph, but I'm still not sure if I've set
the JVM up with the right values to optimise my application - basically, I'm
looking for some advice on what inputOpts I should set when starting the JVM
using JNI. I'm not even sure what options there are! I'm even starting to
question the idea of using JNI at all, as I'm not sure what overhead each
RPG-to-Java call actually adds. It seems almost impossible to get any
banchmarks for this stuff. Any help on this would be most welcome. 
 
Anyway, here's the post... 
 
Hi,
 
I have written a RPG service program that transforms XML [using transform
stylesheets (XSLT)] into SQL insert statements. These are then executed over
the database on the iSeries.
 
To do this I utilise the Java Native Interface (JNI) to create and use java
objects. Basically, I create a transformer object. I then pass the object an
XML stream source to transform, and a stream result to hold the transformed
data.
 
For each transformation (assuming the transformer object does not change) I
have to create a new StreamSource object:
 
To create the stream source object from RPG I have to perform the following
steps:
 
1) Create a String object from the XML file path. (RPG-to-Java)
2) Create a File object from the String. (RPG-to-Java)
3) Free the String object - no longer needed. (RPG-to-Java)
4) Create a StreamSource object from the File object. (RPG-to-Java)
5) Free the File object - no longer needed. (RPG-to-Java)
 
I create a StreamResult object for each job that runs this process, so I
only perfrom the following once:
 
1) Create a String object from the result file path. (RPG-to-Java)
2) Create a File object from the String. (RPG-to-Java)
3) Free the String object - no longer needed. (RPG-to-Java)
4) Create a StreamResult object from the File object. (RPG-to-Java)
5) Free the File object - no longer needed. (RPG-to-Java)
 
Now, this all works fine - I'm just not sure it's running as fast as it
could be - approx 0.2 seconds for each transformation. After a few hundred
transformations it seems to slow down - could this be the Garbage Collector?
I start the JVM manually using JNI (with version 1.4.2 set). I also set the
classpath manually (using putenv). The XML file path is retrieved from a
data queue, and the result file path is created by the program. All RPG
object references are freed one-at-a-time, not by pushing/popping the local
frame. 
 
So, what are the best ways to speed things up???
 
I've considered the following:
A) Create a custom java class that performs the conversions from file path
to StreamSource/StreamResult and just call it with the two byte arrays.
B) Allocate more memory to the JVM - what's the best size? What's the
default size?
C) Run the whole process in java - I could execute the SQL using JDBC. (but
would that just be even slower???)
D) I've not compiled the XML jar files (Xerces.jar, Xalan.jar, etc) because
I believe the JIT compilers are better than CRTJVAPGM. Is this true?
E) I've not copied and compiled jt400.jar to put in my classpath - should I
need to?
 
Basically, does the JNI carry a large overhead? Should I minimise the number
of RPG-to-Java calls by writing a custom class? Should I optimise the java
environment by allocating memory or compiling objects? I need your wise
words.
 
The program source is available if it helps. (We're running at V5R2M0)
 
Thanks
 
Larry Ducie