Benchmark: timing 500 iterations of dbh_insert, dbh_insert_values, sth_insert...
dbh_insert: 20 wallclock secs ( 5.30 usr +  1.41 sys =  6.71 CPU) @ 74.52/s (n=500)
dbh_insert_values: 23 wallclock secs ( 5.62 usr +  1.45 sys =  7.07 CPU) @ 70.72/s (n=500)
sth_insert: 55 wallclock secs (27.53 usr +  2.50 sys = 30.03 CPU) @ 16.65/s (n=500)