holdlocks

tx #1begin transaction
/* acquire a shared lock and hold it until we commit */
1: select col_1 from table_a holdlock where id=1
2: update table_b set col_3 = 'fiz' where id=12
commit transaction

tx #2begin transaction
1: update table_a set col_2 = 'a' where id=1
2: update table_c set col_3 = 'teo' where id=45
commit transaction