Benchmark: timing 500 iterations of dbh_insert, dbh_insert_values, sth_insert...
dbh_insert: 28 wallclock secs ( 5.99 usr +  1.68 sys =  7.67 CPU) @ 65.19/s (n=500)
dbh_insert_values: 27 wallclock secs ( 6.02 usr +  1.82 sys =  7.84 CPU) @ 63.78/s (n=500)
sth_insert: 59 wallclock secs (28.48 usr +  2.41 sys = 30.89 CPU) @ 16.19/s (n=500)