RE: Performance when using POI to create an excel workbook.

Actually, AFAIK you use the JIT compiler by default if you don't use
CRTJVAPGM.  While the best person to answer this would be Blair Wyman, the
way I understand it is that the difference between JIT compiler and
CRTJVAPGM has to do with when the Java byte codes are converted to
executable machine instructions.

According to my imprecise layman's understanding, the JIT compiler is a part
of the standard runtime and whenever a particular section of Java bytecode
is executed "enough" times, the JIT compiler compiles it.  It does this as
optimally as possible in the context in which the bytecode is being used.
Don't ask me the details... optimizing compilers are as close to black magic
as programming gets.

On the other hand, CRTJVAPGM is an offline process that converts the Java
bytecodes to their equivalents but without the benefit of any additional
profiling information.  So it generates executable code that can be used
anywhere, but might not be the best optimizations for a specific use.
However, once you do attach that chunk of machine code to the JAR file, I
*think* it prevents the JIT compiler from doing its thing, and so you always
get that statically (and perhaps suboptimally) generated bytecode.

Now, this is ALL just my understanding, and I'll be the first to say that
while there's a certain level of common sense to what I just laid out, I in
no way profess to understand the inner working... IANACW (I am not a
compiler writer).

Joe


> From: Scott Klement
> 
> Maybe you could tell us how to use the JIT compiler for the same purpose
> so that we could compare the two?