Does jdbc dataset store all rows in jvm memory

Question

I am using a java jdbc application to fetch about 500,000 records from DB. The Database being used is Oracle. I write the data into a file as soon as each row is fetched. Since

Answer 1

It depends. Different drivers may behave differently and different ResultSet settings may behave differently.

If you have a CONCUR_READ_ONLY, FETCH_FORWARD, TYPE_FORWARD_ONLY ResultSet, the driver will almost certainly actively store in memory the number of rows that corresponds to your fetch size (of course data for earlier rows will remain in memory for some period of time until it is garbage collected). If you have a TYPE_SCROLL_INSENSITIVE ResultSet, on the other hand, it is very likely that the driver would store all the data that was fetched in memory in order to allow you to scroll backwards and forwards through the data. That's not the only possible way to implement this behavior, so different drivers (and different versions of drivers) may have different behaviors but it is the simplest and the way that most drivers I've come across behave.