Unpickling crashing my machine

[Pierre-Frédéric Caillaud]

No response, so I'm reposting this ad it seems an "interesting" problem...

I have a huge dataset which contains a lot of individual records  
represented by class instances.

I pickle this to a file :

way #1 :
for object in objects :
	cPickle.dump( object, myfile, -1 )

way #2 :
p = cPickle.Pickler( myfile, -1 )
for object in objects :
	p.dump( object )

When I try to unpickle this big file :

p = cPickle.Unpickler( open( ... ))
many times p.load()... display a progress counter...

Loading the file generated by #1 works fine, with linear speed.
Loading the file generated by #2 :
- the progress counter runs as fast as #1
- eats all memory, then swap
- when eating swap, the progress counter slows down a lot (of course)
- and the process must be killed to save the machine.

I'm talking lots of memory here. The pickled file is about 80 MB, when  
loaded it fits into RAM no problem.
However I killed the #2 when it had already hogged about 700 Mb of RAM,  
and showed no sign of wanting to stop.

What's the problem ?