If you insert records in a loop, the process ram usage grows forever. There seems be a memory leak in the MongoDB PERL Lib. Attached is the simple version of trivial perl script which will eat all the memory on the local machine.
If you add "Devel::Leak" you can see that MogoDB is allocating new memory in every call to collection->save and not releasing it.
This makes MongoDB very dangerous to use with long-running perl process.
CPAN tells me I am using version 0.702.2 of MongoDB. BUT That version is not available in the version list above, so I selected 0.702.1.
This is perl 5, version 14, subversion 2 (v5.14.2) built for x86_64-linux-gnu-thread-multi.