Re: Preferred method to access databases from Servlets

First, I think you'll find the defaults have changed for .jar and .zip
files.

At some point, we decided to
save the compiled programs for these (I forget what
release we changed this, but I think by V4R4, it is the default).
In V4R5, the default will change again to JIT, so the program will
not be added if it doesn't exist in V4R5.  But, you said you were on V4R4,
so unless you were careful in how you invoked Java,
you'll probably find you have one, probably at OPTIMIZE(20).
Opt(20) was chosen so that the implicit compile did not take
too long.

Do DSPJVAPGM '/yourdirectory/yourjar.jar' and see if there's
a Java program attached to your Jar or Zip file after all.

The JAVA command prior to V4R5
will do implicit CRTJVAPGMs unless told to interpret,
something I presume eveyrone knows, but I left out of
my last (long) posting.

Second, it really isn't practical to intermix the CRTJVAPGM
Transformer code and JIT code in the sense of saving the
JIT code.

I've glossed over a few differences that Blair mentioned.
While the JIT versus OPT(40)  works out as I
said in practice, there are actually optimizations
that OPTIMIZE(40) does that even "Hot Spot"
or the IBM JIT process does not do and there are also a few
things the JIT can do that the OPTIMIZE(40) Transformer either
cannot do or can only do with a little more code.

Thus, their outputs are not entirely equivalent.  They interoperate,
but the very fact the code is saved, or not, can affect some
of the code generated.  The Transformer
still comes out on top overall, so it is still a good thing to do
in most cases.  But, the JIT can be a trusty alternative, especially
if you have some huge jar file you've imported from somewhere
and you don't want to kick off a large and costly
CRTJVAPGM at OPTIMIZE(40) to use what may be only a
handful of classes once or twice from that jar file.

I think you'll find that if there is no *PGM behind a given
.class or .zip file, you'll be able to invoke JAVA to do JIT
on those without a *PGM and use the trusty OPT(40)
program on those that have them.  This probably gives
you what you want anyway.  Or, you can invoke
an all-JIT process as well.

But, it does mean that if you want a persistent program, use
the Transformer.  If you want to exploit the throw-away aspect
of dynamic code load, and yet get decent code, then use the JIT.



Larry W. Loen  -   Senior Java and AS/400 Performance Analyst
                          Dept HP4, Rochester MN


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