Looks like the garbage collection is not triggered in time.

Not really :)

Is there some way I can enforce garbage collection?

Not really

Have you faced such a problem?

Yes, I have created circular references that leaked memory, once I fixed my mistakes the problem went away

Read all about it, I did, and it improved my code tremendously :)

Tutorials: Variable Scoping in Perl: the basics,
Coping with Scoping , Mini-Tutorial: Perl's Memory Management,
Lexical scoping like a fox,
Read this if you want to cut your development time in half!,
Closure on Closures , perlref#Circular References,
Memory leaks and circular references,
Circular references and Garbage collection.,
make perl release memory,
about memory management , Re^3: Scope of lexical variables in the main script , Re: What's the weaken here for?,
Devel::Cycle,
Devel::NYTProf,
Devel::Leak Devel::LeakTrace,
WeakRef