Re: Java Memory question
blmblm@myrealbox.com wrote:
Belatedly following up .... Can you explain what you mean by
"physical enough"? My understanding is that a JVM can easily [*]
be asked to provide an amount of heap space that won't fit into
physical memory, or won't fit comfortably with other applications
that are running, so this (virtual versus physical) does seem
like a distinction that's not useless to make.
From the point of view of the application (JVM in this case) the presence of
virtual memory is transparent - it all just looks like RAM and the application
doesn't mess with where it is. By the time the application does access the
memory, it's been swapped into physical RAM, so the application is dealing
only with physical RAM.
What you're calling "virtual" memory is still physical - the application
accesses it via the actual electronic memory chips.
[*] I started to write "happily", but the possible performance
consequences of using more virtual memory than can be held in
physical memory are -- not happy, are they? Possibly it doesn't
Sure they're happy. The consequence is that you get to run programs that
otherwise wouldn't fit into memory.
happen much these days, but it hasn't been that many years since
I encountered such situations in the wild, so to speak.
It happens all the time, in fact right now at this very moment on the computer
you are using to read this.
The problem is when you use more virtual memory than you have secondary
storage to back it up. The whole *point* of virtual memory is to allocate
more memory than you have physically installed, otherwise there'd be no need
for it.
--
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg