$ strace -otrace_ok  perl -MDBD::Pg -e1 
$ ulimit -Sv 16000    # this simulates your non-working environment
$ strace -otrace_err perl -MDBD::Pg -e1 
Can't load '/usr/local/perl/5.8.8/lib/site_perl/5.8.8/x86_64-linux/auto/DBD/Pg/Pg.so' for module DBD::Pg: libpq.so.3: failed to map segment from shared object: Cannot allocate memory at /usr/local/perl/5.8.8/lib/5.8.8/x86_64-linux/DynaLoader.pm line 230.
 at -e line 0
Compilation failed in require.
BEGIN failed--compilation aborted.