Image as database
Keith Hodges
keith_hodges at yahoo.co.uk
Mon Oct 23 21:39:55 UTC 2006
>
> It's news to me that the Java VM supports an object image. Or that any
> real-world system on Java would just load a snapshot of *all* its data
> and save it *in whole* later - I sincerely doubt that.
>
> - Bert -
>
I wrote a system which held a substantial data set in image with no
problems (this was ST/X).
The biggest problem I had was with stdio.h being limited to 255 open
file descriptors in certain situations on Solaris. As a work around I
had to open 256 dummy file descriptors, then open the 700-1000 file
descriptors that I wanted to use. Then close the dummy file descriptors,
so as to leave some in the range 0-255 available for those parts of the
system that required them.
Another team tried a similar project in perl and another team followed
suit in java. Last I heard they reimplemented from scratch in C++. The
java system took a farm of machines to run it. Following this
experience I have no confidence in the java vm, or associated
technologies being able to run anything of any size or complexity.
Smalltalk can load a simulation of over 1000 interacting telecoms units
with a full simulation of all their configurations, cards, alarms, etc,
and load and have running that simulation in about 20 seconds. The time
it takes to load a 200-400Mb image. Which is not long on a big expensive
sun server machine.
I cant imagine even attempting the same in java without requiring a
database backend and all of the overhead that that would entail.
Overall Squeak's vm may not be as fast as ST/X, but I think it does a
pretty good job.
Keith
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