Thanks again.
Now, I can compress the big string by "Compress::Zlib::compress" just like this:

my $f = <DATA>;
my $dest = compress($f);
#print $dest;
__DATA__
big big string
ssssssssssssssssssssssss
mmmmmmmmmmmmmmmmmmmmmmmmm
as long as possible...
[download]

Now i wanna know whether or not the "$dest" can be stored into DB( column type varchar)
And how to recover the original string($f) later.