my $sth_i = $dbh->prepare_cached( "INSERT INTO foo (bar, baz,qux) VALUES(?,?,?)" );
# or
my $sth_u = $dbh->prepare_cached( "UPDATE foo SET bar = ?, baz = ? WHERE qux = ?" );

# make it easy on perl ie declare loop vars outside loop to save create/destroy
# yes it should be optimised but it seems to help speed/memory consumption
my @fields;

# delete irrelevant indexes here before we start the load

open IN, $infile or die $!;
while(<IN>) {
    @field = split "\t";
    # fail fast if you don't want to do anything - even before you chomp
    # lots of loops so every  little bit of saving helps
    $sth_i->execute(@fields[0..2]);
}

# recreate indexes so you are not wasting time doing partial indexing