I am doing some test about objected-relational mapping and something odd came up: when I implement a simple hierarchy test using one table per subclass, with two subclasses, I get a query time of 218.44ms when there are 12000 lines splited in the two tables, but a query time of 1207.56 when I add more 200 lines!
Why is there such a big difference with only 200 aditonal lines? Before 12000 and after 12200 the query time grows slowly.
The query I am running basically makes an union between the two tables and then select one entry by the id.
The querry is generated by Hibernate.