Re: [Vtd-xml-users] Storing parsing info

[Tatu S. <cow...@ya...>]

--- Fernando Gonzalez <fer...@gm...> wrote:

> Well, jeje, the computer is new but I don't think my
> disk is so fast. I
> think Java or the operating system has to cache
> something because the first
> time I load the file it takes a bit more than 2
> seconds and after the first
> load, it only takes 300ms to read the file...
> I have no experience on doing benchmarks and maybe
> I'm am missing something.
> That's why I attached the program.

One thing you need to know is that JVM's HotSpot does
incremental optimization. As such, calling anything
first time (or, rather, first N, where N can be like
2000 times) will take much much longer. This because
code at first will be interpreted from byte code. Only
after JVM notices particular part code is so-called
"hot spot" (called so often it is where most time is
spent) it will inline it to native code.

Because of this, one must always ensure that there is
enough of so-called warmup time to reach steady state
performance. That is, unless your use case is such
where you only run things once, using separate JVM
instance.

So it perfectly normal (and expected) that
loading+parsing things first time is significantly
slower than second time around.
If you want to ensure it's not due to OS-level disk
block caching (which also affects results), you can
warm things up using different xml files: code paths
should be same or similar, so HotSpot will optimize
code, but data is different, so OS won't be able to
cache it.

Hope this helps,

-+ Tatu +-



 
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