Comment: Because it is (Score 1) on 2009.02.11 16:42
Does the CPAN shell perhaps try to keep the whole module database in RAM?
Yes, that's how it does some of the query commands it implements. It has been so for a long time now. And yes, under-powered computers may have problems with that. (But it can be worse - CPANPLUS is much heavier or at least was, a long time ago when I tried it.)
CPAN.pm has an experimental support for the module database in a SQLite db, as implemented by CPAN::SQLite. It decreases the memory consumption. You can try that.