# 1
perl -MFcntl -MDB_File -e"tie%a,'DB_File','rat.test',O_CREAT|O_RDWR or die $!;for(1..1_000){select undef,undef,undef,.01;$a{a}++;}"

# 2
perl -MFcntl -MDB_File -e"tie%a,'DB_File','rat.test',O_RDONLY or die $!;warn $a{a}"