Stas Bekman wrote:
> On Wed, 19 Apr 2000, Matt Carothers wrote:
> > On Tue, 18 Apr 2000, Stas Bekman wrote:
> >
> > > Let's assume that you have two different sets of scripts/code
> > > which have a little or nothing in common at all (different
> > > modules, no base code sharing), the basic mod_perl process
> > > before the code have been loaded of three Mbytes and each code
> > > base adds ten Mbytes when loaded. Which makes each process 23Mb
> > > in size when all the code gets loaded.
> >
> > Can't you share most of that 23mb between the processes by
> > pre-loading the scripts/modules in your startup.pl? I'd say the
> > main advantage of engineering dissimilar services as if they were
> > on separate servers is scalability rather than memory use. When a
> > site outgrows the hardware it's on, spreading it out to multiple
> > machines requires a lot less ankle grabbing if it was designed
> > that way to begin with. :)
>
> Geez, I always forget something :(
>
> You are right. I forgot to mention that this was a scenario for the
> 23 Mb of unshared memory. I just wanted to give an example. Still
> somehow I'm almost sure that there are servers where even with
> sharing in place, the hypothetical scenario I've presented is quite
> possible.
>
> Anyway, it's just another patent for squeezing some more juice from
> your hardware without upgrading it.
>
> But, sure I'll add the correction about the sharing memory which
> drastically changes the story :)
>
Actually in my experience the sharing of memory doesn't work as well
as one would hope. While compiling perl allocates memory for code
and data (variables) from the same memory pools, so code and
variables are interlaced. Over the lifetime of a apache/mod_perl
child a lot of memory pages are promoted from shared to unshared that
contain mostly code and one or two variables... If someone with more
knowledge of the perl internals were to change that, this would make
a huge difference for mod_perl users and everybody else writing
daemons in perl that spawn many children.
Gerd
